THE "HOW-TO-DO-IT" BOOKS ELECTRICITY FOR BOYS [Illustration: Fig. 1. WORK BENCH] THE "HOW-TO-DO-IT" BOOKS ELECTRICITY FOR BOYS A working guide, in the successivesteps of electricity, described insimple terms WITH MANY ORIGINAL ILLUSTRATIONS By J. S. ZERBE, M. E. AUTHOR OFCARPENTRY FOR BOYSPRACTICAL MECHANICS FOR BOYS [Illustration: Printer's Mark] THE NEW YORK BOOK COMPANYNEW YORK COPYRIGHT, 1914, BYTHE NEW YORK BOOK COMPANY CONTENTS INTRODUCTORY Page 1 I. ELECTRICITY CONSIDERED. BRIEF HISTORICALEVENTS Page 5 The Study of Electricity. First Historical Accounts. Bottling Electricity. Discovery of Galvanic Electricity. Electro-motive Force. Measuring Instruments. Rapidity of Modern Progress. How to Acquire the Vast Knowledge. The Means Employed. II. WHAT TOOLS AND APPARATUS ARE NEEDED Page 11 Preparing the Workshop. Uses of Our Workshop. What to Build. What to Learn. Uses of the Electrical Devices. Tools. Magnet-winding Reel. III. MAGNETS, COILS, ARMATURES, ETC. Page 18 The Two Kinds of Magnets. Permanent Magnets. Electro-Magnets. Magnetism. Materials for Magnets. Non-magnetic Material. Action of a _Second_ Magnet. What North and South Pole Mean. Repulsion and Attraction. Positives and Negatives. Magnetic Lines of Force. The Earth as a Magnet. Why the Compass Points North and South. Peculiarity of a Magnet. Action of the Electro-Magnet. Exterior Magnetic Influence Around a Wires Carrying a Current. Parallel Wires. IV. FRICTIONAL, VOLTAIC OR GALVANIC AND ELECTRO-MAGNETICELECTRICITY Page 29 Three Electrical Sources. Frictional Electricity. Leyden Jar. Voltaic or Galvanic Electricity. Voltaic Pile; How Made. Plus and Minus Signs. The Common Primary Cell. Battery Resistance. Electrolyte and Current. Electro-magnetic Electricity. Magnetic Radiation. Different Kinds of Dynamos. Direct Current Dynamos. Simple Magnet Construction. How to Wind. The Dynamo Fields. The Armature. Armature Windings. Mounting the Armature. The Commutator. Commutator Brushes. Dynamo Windings. The Field. Series-wound Field. Shunt-wound. Compound-wound. V. HOW TO DETECT AND MEASURE ELECTRICITY Page 49 Measuring Instruments. The Detector. Direction of Current. Simple Current Detector. How to Place the Detector. Different Ways to Measure a Current. The Sulphuric Acid Voltameter. The Copper Voltameter. The Galvanoscope Electro-magnetic Method. The Calorimeter. The Light Method. The Preferred Method. How to Make a Sulphuric Acid Voltameter. How to Make a Copper Voltameter. Objections to the Calorimeter. VI. VOLTS, AMPERES, OHMS AND WATTS Page 60 Understanding Terms. Intensity and Quantity. Voltage. Amperage Meaning of Watts and Kilowatt. AStandard of Measurement. The Ampere Standard. TheVoltage Standard. The Ohm. Calculating the Voltage. VII. PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS ANDLIKE APPARATUS Page 65 Simple Switches. A Two-Pole Switch. Double-Pole Switch. Sliding Switch. Reversing Switch. Push Buttons. Electric Bells. How Made. How Operated. Annunciators. Burglar Alarm. Wire Circuiting. Circuiting System with Two Bells and Push Buttons. The Push Buttons, Annunciators and Bells. Wiring Up a House. VIII. ACCUMULATORS, STORAGE OR SECONDARY BATTERIES Page 82 Storing Up Electricity. The Accumulator. Accumulator Plates. The Grid. The Negative Pole. Connecting Up the Plates. Charging the Cells. The Initial Charge. The Charging Current. IX. THE TELEGRAPH Page 90 Mechanism in Telegraph Circuit. The Sending Key. The Sounder. Connecting Up the Key and Sounder. Two Stations in Circuit. The Double Click. Illustrating the Dot and the Dash. The Morse Telegraph Code. Example in Use. X. HIGH-TENSION APPARATUS, CONDENSERS, ETC. Page 98 Induction. Low and High Tension. Elastic Property of Electricity. The Condenser. Connecting up a Condenser. The Interrupter. Uses of High-tension Coils. XI. WIRELESS TELEGRAPHY Page 104 Telegraphing Without Wires. Surging Character of High-tension Currents. The Coherer. How Made. The Decoherer. The Sending Apparatus. The Receiving Apparatus. How the Circuits are Formed. XII. THE TELEPHONE Page 110 Vibrations. The Acoustic Telephone. Sound Waves. Hearing Electricity. The Diaphragm in a Magnetic Field. A Simple Telephone Circuit. How to Make a Telephone. Telephone Connections. Complete Installation. The Microphone. Light Contact Points. How to Make a Microphone. Microphone, the Father of the Transmitter. Automatic Cut-outs for Telephones. Complete Circuiting with Transmitters. XIII. ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING Page 123 Decomposing Liquids. Making Hydrogen and Oxygen. Purifying Water. Rust. Oxygen as a Purifier. Composition of Water. Common Air Not a Good Purifier. Pure Oxygen a Water Purifier. The Use of Hydrogen in Purification. Aluminum Electrodes. Electric Hand Purifier. Purification and Separation of Metals. Electroplating. Plating Iron with Copper. Direction of Current. XIV. ELECTRIC HEATING. THERMO-ELECTRICITY Page 135 Generating Heat in a Wire. Resistance of Substances. Signs of Connectors. Comparison of Metals. A Simple Electric Heater. How to Arrange for Quantity of Current Used. An Electric Iron. Thermo-Electricity Converting Heat Directly into Electricity Metals. Electric, Positive, Negative. Thermo-electric Coupler. XV. ALTERNATING CURRENTS, CHOKING COIL, TRANSFORMER Page 145 Direct Current. Alternating Current. The Magnetic Field. Action of a Magnetized Wire. The Movement of a Current in a Charged Wire. Current Reversing Itself. Self-Induction. Brushes in a Direct Current Dynamo: Alternating, Positive and Negative Poles. How an Alternating Current Dynamo is Made. The Windings. The Armature Wires. Choking Coils. The Transformer. How the Voltage is Determined. Voltage and Amperage in Transformers. XVI. ELECTRIC LIGHTING Page 161 Early conditions. Fuels. Reversibility of Dynamo. Electric arc. Mechanism to maintain the arc. Resistance coil. Parallel carbons for making arc. Series current. Incandescent system. Multiple circuit. Subdivision of electric light. The filament. The glass bulb. Metallic filaments. Vapor lamps. Directions for improvements. Heat in electric lighting. Curious superstitions concerning electricity. Magnetism. Amber. Discovery of the properties of a magnet. Electricity in mountain regions. Early beliefs as to magnetism and electricity. The lightning rod. Protests against using it. Pliny's explanation of electricity. XVII. POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS Page 175 Early beliefs concerning the dynamo. Experiments with magnets. Physical action of dynamo and motor. Electrical influence in windings. Comparing motor and dynamo. How the current acts in a dynamo. Its force in a motor. Loss in power transmission. The four ways in which power is dissipated. Disadvantages of electric power. Its advantages. Transmission of energy. High voltages. The transformer. Step-down transformers. Electric furnaces. Welding by electricity. Merging the particles of the joined ends. XVIII. X-RAY, RADIUM AND THE LIKE Page 184 The camera and the eye. Actinic rays. Hertzian waves. High-tension apparatus. Vacuum tubes. Character of the ultra-violet rays. How distinguished. The infra-red rays. Their uses. X-rays not capable of reflection. Not subject to refraction. Transmission through opaque substances. Reducing rates of vibration. Radium. Radio-activity. Radio-active materials. Pitchblende. A new form of energy. Electrical source. Healing power. Problems for scientists. LIST OF ILLUSTRATIONS FIG. 1. Work bench Frontispiece PAGE 2. Top of magnet-winding reel 14 3. Side of magnet-winding reel 14 4. Journal block 15 5. Plain magnet bar 19 6. Severed magnet 20 7. Reversed magnets 21 8. Horseshoe magnet 22 9. Earth's magnetic lines 23 10. Two permanent magnets 24 11. Magnets in earth's magnetic field 24 12. Armatures for magnets 25 13. Magnetized field 26 14. Magnetized bar 26 15. Direction of current 27 16. Direction of induction current 28 17. Frictional-electricity machine 30 18. Leyden jar 32 19. Galvanic electricity. Crown of cups 33 20. Voltaic electricity 34 21. Primary battery 36 22. Dynamo field and pole piece 39 23. Base and fields assembled 41 24. Details of the armature, core 42 25. Details of the armature, body 42 26. Armature Journals 43 27. Commutator 43 28. End view of armature, mounted 44 29. Top view of armature on base 45 30. Field winding 47 31. Series-wound 47 32. Shunt-wound 48 33. Compound-wound 48 34. Compass magnet, swing to the right 50 35. Magnetic compass 50 36. Magnet, swing to the left 50 37. Indicating direction of current 51 38. The bridge of the detector 52 39. Details of detector 53 40. Cross-section of detector 54 41. Acid voltameter 56 42. Copper voltameter 56 43. Two-pole switch 66 44. Double-pole switch 66 45. Sliding switch 67 46. Rheostat form of switch 68 47. Reversing switch 69 48. Push button 70 49. Electric bell 71 50. Armature of electric bell 72 51. Vertical section of annunciator 72 52. Front view of annunciator 72 53. Horizontal section of annunciator 72 54. Front plate of annunciator 72 55. Alarm switch on window 76 56. Burglar alarm on window 76 57. Burglar alarm contact 77 58. Neutral position of contact 78 59. Circuiting for electric bell 79 60. Annunciators in circuit 80 61. Wiring system for a house 80 62. Accumulator grids 83 63. Assemblage of accumulator grids 85 64. Connecting up storage battery in series 87 65. Parallel series 88 66. Charging circuit 88 67. Telegraph sending key 91 68. Telegraph sounder 92 69. A telegraph circuit 94 70. Induction coil and circuit 99 71. Illustrating elasticity 100 72. Condenser 101 73. High-tension circuit 102 74. Current interrupter 103 75. Wireless-telegraphy coherer 105 76. Wireless sending-apparatus 107 77. Wireless receiving-apparatus 108 78. Acoustic telephone 111 79. Illustrating vibrations 111 80. The magnetic field 112 81. Section of telephone receiver 114 82. The magnet and receiver head 115 83. Simple telephone connection 116 84. Telephone stations in circuit 117 85. Illustrating light contact points 118 86. The microphone 119 87. The transmitter 119 88. Complete telephone circuit 121 89. Device for making hydrogen and oxygen 124 90. Electric-water purifier 127 91. Portable electric purifier 129 92. Section of positive plate 130 93. Section of negative plate 130 94. Positive and negative in position 130 95. Form of the insulator 130 96. Simple electric heater 137 97. Side view of resistance device 139 98. Top view of resistance device 139 99. Plan view of electric iron 140100. Section of electric iron 141101. Thermo-electric couple 143102. Cutting a magnetic field 146103. Alternations, first position 148104. Alternations, second position 148105. Alternations, third position 148106. Alternations, fourth position 148107. Increasing alternations, first view 149108. Increasing alternations, second view 149109. Connection of alternating dynamo armature 150110. Direct current dynamo 151111. Circuit wires in direct current dynamo 152112. Alternating polarity lines 154113. Alternating current dynamo 155114. Choking coil 157115. A transformer 158116. Parallel carbons 164117. Arc-lighting circuit 165118. Interrupted conductor 166119. Incandescent circuit 167120. Magnetic action in dynamo, 1st 177121. Magnetic action in dynamo, 2d 177122. Magnetic action in dynamo, 3d 178123. Magnetic action in dynamo, 4th 178124. Magnetic action in motor, 1st 179125. Magnetic action in motor, 2d 179126. Magnetic action in motor, 3d 180127. Magnetic action in motor, 4th 180 INTRODUCTORY Electricity, like every science, presents two phases to the student, onebelonging to a theoretical knowledge, and the other which pertains tothe practical application of that knowledge. The boy is directlyinterested in the practical use which he can make of this wonderfulphenomenon in nature. It is, in reality, the most successful avenue by which he may obtain thetheory, for he learns the abstract more readily from concrete examples. It is an art in which shop practice is a greater educator than can bepossible with books. Boys are not, generally, inclined to speculate ortheorize on phenomena apart from the work itself; but once put them intocontact with the mechanism itself, let them become a living part of it, and they will commence to reason and think for themselves. It would be a dry, dull and uninteresting thing to tell a boy thatelectricity can be generated by riveting together two pieces ofdissimilar metals, and applying heat to the juncture. But put into hishands the metals, and set him to perform the actual work of riveting themetals together, then wiring up the ends of the metals, heating them, and, with a galvanometer, watching for results, it will at once make himsee something in the experiment which never occurred when the abstracttheory was propounded. He will inquire first what metals should be used to get the bestresults, and finally, he will speculate as to the reasons for thephenomena. When he learns that all metals are positive-negative ornegative-positive to each other, he has grasped a new idea in the realmof knowledge, which he unconsciously traces back still further, only tolearn that he has entered a field which relates to the constitution ofmatter itself. As he follows the subject through its various channels hewill learn that there is a common source of all things; a manifestationcommon to all matter, and that all substances in nature are linkedtogether in a most wonderful way. An impulse must be given to a boy's training. The time is past for therule-and-rote method. The rule can be learned better by a manualapplication than by committing a sentence to memory. In the preparation of this book, therefore, I have made practice andwork the predominating factors. It has been my aim to suggest the bestform in which to do the things in a practical way, and from that work, as the boy carries it out, to deduce certain laws and develop theprinciples which underlie them. Wherever it is deemed possible to do so, it is planned to have the boy make these discoveries for himself, so asto encourage him to become a thinker and a reasoner instead of a meremachine. A boy does not develop into a philosopher or a scientist through beingtold he must learn the principles of this teaching, or the fundamentalsof that school of reasoning. He will unconsciously imbibe the spirit andthe willingness if we but place before him the tools by which he maybuild even the simple machinery that displays the various electricalmanifestations. CHAPTER I THE STUDY OF ELECTRICITY. HISTORICAL There is no study so profound as electricity. It is a marvel to thescientist as well as to the novice. It is simple in its manifestations, but most complex in its organization and in its ramifications. It hasbeen shown that light, heat, magnetism and electricity are the same, butthat they differ merely in their modes of motion. FIRST HISTORICAL ACCOUNT. --The first historical account of electricitydates back to 600 years B. C. Thales of Miletus was the first todescribe the properties of amber, which, when rubbed, attracted andrepelled light bodies. The ancients also described what was probablytourmaline, a mineral which has the same qualities. The torpedo, a fishwhich has the power of emitting electric impulses, was known in veryearly times. From that period down to about the year 1600 no accounts of anyhistorical value have been given. Dr. Gilbert, of England, made a numberof researches at that time, principally with amber and other materials, and Boyle, in 1650, made numerous experiments with frictionalelectricity. Sir Isaac Newton also took up the subject at about the same period. In1705 Hawksbee made numerous experiments; also Gray, in 1720, and aWelshman, Dufay, at about the same time. The Germans, from 1740 to 1780, made many experiments. In 1740, at Leyden, was discovered the jar whichbears that name. Before that time, all experiments began and ended withfrictional electricity. The first attempt to "bottle" electricity was attempted byMuschenbr[oe]ck, at Leyden, who conceived the idea that electricity inmaterials might be retained by surrounding them with bodies which didnot conduct the current. He electrified some water in a jar, andcommunication having been established between the water and the primeconductor, his assistant, who was holding the bottle, on trying todisengage the communicating wire, received a sudden shock. In 1747 Sir William Watson fired gunpowder by an electric spark, and, later on, a party from the Royal Society, in conjunction with Watson, conducted a series of experiments to determine the velocity of theelectric fluid, as it was then termed. Benjamin Franklin, in 1750, showed that lightning was electricity, andlater on made his interesting experiments with the kite and the key. DISCOVERING GALVANIC ELECTRICITY. --The great discovery of Galvani, in1790, led to the recognition of a new element in electricity, calledgalvanic or voltaic (named after the experimenter, Volta), and now knownto be identical with frictional electricity. In 1805 Poisson was thefirst to analyze electricity; and when [OE]rsted of Copenhagen, in 1820, discovered the magnetic action of electricity, it offered a greatstimulus to the science, and paved the way for investigation in a newdirection. Ampere was the first to develop the idea that a motor or adynamo could be made operative by means of the electro-magnetic current;and Faraday, about 1830, discovered electro-magnetic rotation. ELECTRO-MAGNETIC FORCE. --From this time on the knowledge of electricitygrew with amazing rapidity. Ohm's definition of electro-motive force, current strength and resistance eventuated into Ohm's law. Thomsongreatly simplified the galvanometer, and Wheatstone invented therheostat, a means of measuring resistance, about 1850. Then primarybatteries were brought forward by Daniels, Grove, Bunsen and Thomson, and electrolysis by Faraday. Then came the instruments of precision--theelectrometer, the resistance bridge, the ammeter, the voltmeter--all ofthe utmost value in the science. MEASURING INSTRUMENTS. --The perfection of measuring instruments did moreto advance electricity than almost any other field of endeavor; so thatafter 1875 the inventors took up the subject, and by their energydeveloped and put into practical operation a most wonderful array ofmechanism, which has become valuable in the service of man in almostevery field of human activity. RAPIDITY OF MODERN PROGRESS. --This brief history is given merely to showwhat wonders have been accomplished in a few years. The art is reallyless than fifty years old, and yet so rapidly has it gone forward thatit is not at all surprising to hear the remark, that the end of thewonders has been reached. Less than twenty-five years ago a highofficial of the United States Patent Office stated that it was probablethe end of electrical research had been reached. The most wonderfuldevelopments have been made since that time; and now, as in the past, one discovery is but the prelude to another still more remarkable. Weare beginning to learn that we are only on the threshold of thatstorehouse in which nature has locked her secrets, and that there is nolimit to human ingenuity. HOW TO ACQUIRE THE VAST KNOWLEDGE. --As the boy, with his limited vision, surveys this vast accumulation of tools, instruments and machinery, andsees what has been and is now being accomplished, it is not to bewondered at that he should enter the field with timidity. In his mindthe great question is, how to acquire the knowledge. There is so much tolearn. How can it be accomplished? The answer to this is, that the student of to-day has the advantage ofthe knowledge of all who have gone before; and now the pertinent thingis to acquire that knowledge. THE MEANS EMPLOYED. --This brings us definitely down to an examination ofthe means that we shall employ to instil this knowledge, so that it maybecome a permanent asset to the student's store of information. The most significant thing in the history of electrical development isthe knowledge that of all the great scientists not one of them everadded any knowledge to the science on purely speculative reasoning. Allof them were experimenters. They practically applied and developed theirtheories in the laboratory or the workshop. The natural inference is, therefore, that the boy who starts out to acquire a knowledge ofelectricity, must not only theorize, but that he shall, primarily, conduct the experiments, and thereby acquire the information in apractical way, one example of which will make a more lasting impressionthan pages of dry text. Throughout these pages, therefore, I shall, as briefly as possible, point out the theories involved, as a foundation for the work, and thenillustrate the structural types or samples; and the work is so arrangedthat what is done to-day is merely a prelude or stepping-stone to thenext phase of the art. In reality, we shall travel, to a considerableextent, the course which the great investigators followed when they weregroping for the facts and discovering the great manifestations innature. CHAPTER II WHAT TOOLS AND APPARATUS ARE NEEDED PREPARING THE WORKSHOP. --Before commencing actual experiments we shouldprepare the workshop and tools. Since we are going into this work aspioneers, we shall have to be dependent upon our own efforts for theproduction of the electrical apparatus, so as to be able, with ourhome-made factory, to provide the power, the heat and the electricity. Then, finding we are successful in these enterprises, we may lookforward for "more worlds to conquer. " By this time our neighbors will become interested in and solicit workfrom us. USES OF OUR WORKSHOPS. --They may want us to test batteries, and it thenbecomes necessary to construct mechanism to detect and measureelectricity; to install new and improved apparatus; and to put in andconnect up electric bells in their houses, as well as burglar alarms. Tomeet the requirements, we put in a telegraph line, having learned, aswell as we are able, how they are made and operated. But we find thetelegraph too slow and altogether unsuited for our purposes, as well asfor the uses of the neighborhood, so we conclude to put in a telephonesystem. WHAT TO BUILD. --It is necessary, therefore, to commence right at thebottom to build a telephone, a transmitter, a receiver and aswitch-board for our system. From the telephone we soon see thedesirability of getting into touch with the great outside world, andwireless telegraphy absorbs our time and energies. But as we learn more and more of the wonderful things electricity willdo, we are brought into contact with problems which directly interestthe home. Sanitation attracts our attention. Why cannot electricity actas an agent to purify our drinking water, to sterilize sewage and toarrest offensive odors? We must, therefore, learn something about thesubject of electrolysis. WHAT TO LEARN. --The decomposition of water is not the only thing that weshall describe pertaining to this subject. We go a step further, andfind that we can decompose metals as well as liquids, and that we canmake a pure metal out of an impure one, as well as make the foulestwater pure. But we shall also, in the course of our experiments, findthat a cheap metal can be coated with a costly one by means ofelectricity--that we can electroplate by electrolysis. USES OF THE ELECTRICAL DEVICES. --While all this is progressing and ourfactory is turning out an amazing variety of useful articles, we are ledto inquire into the uses to which we may devote our surplus electricity. The current may be diverted for boiling water; for welding metals; forheating sad-irons, as well as for other purposes which are dailyrequired. TOOLS. --To do these things tools are necessary, and for the present theyshould not be expensive. A small, rigidly built bench is the firstrequirement. This may be made, as shown in Fig. 1, of three 2-inchplanks, each 10 inches wide and 6 feet long, mounted on legs 36 inchesin height. In the front part are three drawers for your material, or thesmall odds and ends, as well as for such little tools as you mayaccumulate. Then you will need a small vise, say, with a 2-inch jaw, andyou will also require a hand reel for winding magnets. This will befully described hereafter. You can also, probably, get a small, cheap anvil, which will be of thegreatest service in your work. It should be mounted close up to the workbench. Two small hammers, one with an A-shaped peon, and the other witha round peon, should be selected, and also a plane and a small wood sawwith fine teeth. A bit stock, or a ratchet drill, if you can afford it, with a variety of small drills; two wood chisels, say of 3/8-inch and3/4-inch widths; small cold chisels; hack saw, 10-inch blade; smalliron square; pair of dividers; tin shears; wire cutters; 2 pairs ofpliers, one flat and the other round-nosed; 2 awls, centering punch, wire cutters, and, finally, soldering tools. [Illustration: _Fig. 2. Top View_ MAGNET-WINDING REEL] [Illustration: _Fig. 3. Side View_ MAGNET-WINDING REEL] If a gas stove is not available, a brazing torch is an essential tool. Numerous small torches are being made, which are cheap and easilyoperated. A small soldering iron, with pointed end, should be provided;also metal shears and a small square; an awl and several sizes ofgimlets; a screwdriver; pair of pliers and wire cutters. From the foregoing it will be seen that the cost of tools is not a veryexpensive item. This entire outfit, not including the anvil and vise, may be purchasednew for about $20. 00, so we have not been extravagant. MAGNET-WINDING REEL. --Some little preparation must be made, so we may beenabled to handle our work by the construction of mechanical aids. [Illustration: _Fig. 4. Journal Block. _] First of these is the magnet-winding reel, a plan view of which is shownin Fig. 2. This, for our present work, will be made wholly of wood. Select a plank 1-1/2 inches thick and 8 inches wide, and from this cutoff two pieces (A), each 7 inches long, and then trim off the corners(B, B), as shown in Fig. 4. To serve as the mandrel (C, Fig. 2), selecta piece of broomstick 9 inches long. Bore a hole (D) in each block (A) ahalf inch below the upper margin of the block, this hole being of suchdiameter that the broomstick mandrel will fit and easily turn therein. Place a crank (E), 5 inches long, on the outer end of the mandrel, as inFig. 3. Then mount one block on the end of the bench and the other block3 inches away. Affix them to the bench by nails or screws, preferablythe latter. On the inner end of the mandrel put a block (F) of hard wood. This isdone by boring a hole 1 inch deep in the center of the block, into whichthe mandrel is driven. On the outer face of the block is a square holelarge enough to receive the head of a 3/8-inch bolt, and into thedepression thus formed a screw (G) is driven through the block and intothe end of the mandrel, so as to hold the block (F) and mandrel firmlytogether. When these parts are properly put together, the inner side ofthe block will rest and turn against the inner journal block (A). The tailpiece is made of a 2" × 4" scantling (H), 10 inches long, oneend of it being nailed to a transverse block (I) 2" × 2" × 4". The innerface of this block has a depression in which is placed a V-shaped cup(J), to receive the end of the magnet core (K) or bolt, which is to beused for this purpose. The tailpiece (H) has a longitudinal slot (L) 5inches long adapted to receive a 1/2-inch bolt (M), which passes downthrough the bench, and is, therefore, adjustable, so it may be moved toand from the journal bearing (A), thereby providing a place for thebolts to be put in. These bolts are the magnet cores (K), 6 inches long, but they may be even longer, if you bore several holes (N) through thebench so you may set over the tailpiece. With a single tool made substantially like this, over a thousand of thefinest magnets have been wound. Its value will be appreciated after youhave had the experience of winding a few magnets. ORDER IN THE WORKSHOP. --Select a place for each tool on the rear uprightof the bench, and make it a rule to put each tool back into its placeafter using. This, if persisted in, will soon become a habit, and willsave you hours of time. Hunting for tools is the unprofitable part ofany work. CHAPTER III MAGNETS, COILS, ARMATURES, ETC. THE TWO KINDS OF MAGNET. --Generally speaking, magnets are of two kinds, namely, permanent and electro-magnetic. PERMANENT MAGNETS. --A permanent magnet is a piece of steel in which anelectric force is exerted at all times. An electro-magnet is a piece ofiron which is magnetized by a winding of wire, and the magnet isenergized only while a current of electricity is passing through thewire. ELECTRO-MAGNET. --The electro-magnet, therefore, is the more useful, because the pull of the magnet can be controlled by the current whichactuates it. The electro-magnet is the most essential of all contrivances in theoperation and use of electricity. It is the piece of mechanism whichdoes the physical work of almost every electrical apparatus or machine. It is the device which has the power to convert the unseen electriccurrent into motion which may be observed by the human eye. Without itelectricity would be a useless agent to man. While the electro-magnet is, therefore, the form of device which isalmost wholly used, it is necessary, first, to understand the principlesof the permanent magnet. MAGNETISM. --The curious force exerted by a magnet is called magnetism, but its origin has never been explained. We know its manifestationsonly, and laws have been formulated to explain its various phases; howto make it more or less intense; how to make its pull more effective;the shape and form of the magnet and the material most useful in itsconstruction. [Illustration: _Fig 5. _ PLAIN MAGNET BAR] MATERIALS FOR MAGNETS. --Iron and steel are the best materials formagnets. Some metals are non-magnetic, this applying to iron if combinedwith manganese. Others, like sulphur, zinc, bismuth, antimony, gold, silver and copper, not only are non-magnetic, but they are actuallyrepelled by magnetism. They are called the diamagnetics. NON-MAGNETIC MATERIALS. --Any non-magnetic body in the path of a magneticforce does not screen or diminish its action, whereas a magneticsubstance will. In Fig. 5 we show the simplest form of magnet, merely a bar of steel (A)with the magnetic lines of force passing from end to end. It will beunderstood that these lines extend out on all sides, and not only alongtwo sides, as shown in the drawing. The object is to explain clearly howthe lines run. [Illustration: _Fig. 6. _ SEVERED MAGNET] ACTION OF A SEVERED MAGNET. --Now, let us suppose that we sever this barin the middle, as in Fig. 6, or at any other point between the ends. Inthis case each part becomes a perfect magnet, and a new north pole (N)and a new south pole (S) are made, so that the movement of the magneticlines of force are still in the same direction in each--that is, thecurrent flows from the north pole to the south pole. WHAT NORTH AND SOUTH POLES MEAN. --If these two parts are placed closetogether they will attract each other. But if, on the other hand, one ofthe pieces is reversed, as in Fig. 7, they will repel each other. Fromthis comes the statement that likes repel and unlikes attract eachother. REPULSION AND ATTRACTION. --This physical act of repulsion and attractionis made use of in motors, as we shall see hereinafter. It will be well to bear in mind that in treating of electricity thenorth pole is always associated with the plus sign (+) and the southpole with the minus sign (-). Or the N sign is positive and the S signnegative electricity. [Illustration: _Fig. 7. _ REVERSED MAGNETS] POSITIVES AND NEGATIVES. --There is really no difference between positiveand negative electricity, so called, but the foregoing method merelyserves as a means of identifying or classifying the opposite ends of amagnet or of a wire. MAGNETIC LINES OF FORCE. --It will be noticed that the magnetic lines offorce pass through the bar and then go from end to end through theatmosphere. Air is a poor conductor of electricity, so that if we canfind a shorter way to conduct the current from the north pole to thesouth pole, the efficiency of the magnet is increased. This is accomplished by means of the well-known horseshoe magnet, wherethe two ends (N, S) are brought close together, as in Fig. 8. THE EARTH AS A MAGNET. --The earth is a huge magnet and the magneticlines run from the north pole to the south pole around all sides of theglobe. [Illustration: _Fig. 8. _ HORSESHOE MAGNET] The north magnetic pole does not coincide with the true north pole orthe pivotal point of the earth's rotation, but it is sufficiently nearfor all practical purposes. Fig. 9 shows the magnetic lines running fromthe north to the south pole. WHY THE COMPASS POINTS NORTH AND SOUTH. --Now, let us try to ascertainwhy the compass points north and south. Let us assume that we have a large magnet (A, Fig. 10), and suspend asmall magnet (B) above it, so that it is within the magnetic field ofthe large magnet. This may be done by means of a short pin (C), which islocated in the middle of the magnet (B), the upper end of this pinhaving thereon a loop to which a thread (D) is attached. The pin alsocarries thereon a pointer (E), which is directed toward the north poleof the bar (B). [Illustration: _Fig. 9. _ EARTH'S MAGNETIC LINES] You will now take note of the interior magnetic lines (X), and theexterior magnetic lines (Z) of the large magnet (A), and compare thedirection of their flow with the similar lines in the small magnet (B). The small magnet has both its exterior and its interior lines within theexterior lines (Z) of the large magnet (A), so that as the small magnet(B) is capable of swinging around, the N pole of the bar (B) will pointtoward the S pole of the larger bar (A). The small bar, therefore, isinfluenced by the exterior magnetic field (Z). [Illustration: _Fig. 10. _ TWO PERMANENT MAGNETS] [Illustration: _Fig. 11. _ MAGNETS IN THE EARTH'S MAGNETIC FIELD] Let us now take the outline represented by the earth's surface (Fig. 11), and suspend a magnet (A) at any point, like the needle of acompass, and it will be seen that the needle will arrange itself northand south, within the magnetic field which flows from the north to thesouth pole. PECULIARITY OF A MAGNET. --One characteristic of a magnet is that, whileapparently the magnetic field flows out at one end of the magnet, andmoves inwardly at the other end, the power of attraction is just thesame at both ends. In Fig. 12 are shown a bar (A) and a horseshoe magnet (B). The bar (A)has metal blocks (C) at each end, and each of these blocks is attractedto and held in contact with the ends by magnetic influence, just thesame as the bar (D) is attracted by and held against the two ends of thehorseshoe magnet. These blocks (C) or the bar (D) are called armatures. Through them is represented the visible motion produced by the magneticfield. [Illustration: _Fig. 12. _ ARMATURES FOR MAGNETS] ACTION OF THE ELECTRO-MAGNET. --The electro-magnet exerts its force inthe same manner as a permanent magnet, so far as attraction andrepulsion are concerned, and it has a north and a south pole, as in thecase with the permanent magnet. An electro-magnet is simply a bar ofiron with a coil or coils of wire around it; when a current ofelectricity flows through the wire, the bar is magnetized. The momentthe current is cut off, the bar is demagnetized. The question that nowarises is, why an electric current flowing through a wire, under thoseconditions, magnetizes the bar, or _core_, as it is called. [Illustration: _Fig. 13. _ MAGNETIZED FIELD] [Illustration: _Fig. 14. _ MAGNETIZED BAR] In Fig. 13 is shown a piece of wire (A). Let us assume that a current ofelectricity is flowing through this wire in the direction of the darts. What actually takes place is that the electricity extends out beyond thesurface of the wire in the form of the closed rings (B). If, now, thiswire (A) is wound around an iron core (C, Fig. 14), you will observethat this electric field, as it is called, entirely surrounds the core, or rather, that the core is within the magnetic field or influence ofthe current flowing through the wire, and the core (C) thereby becomesmagnetized, but it is magnetized only when the current passes throughthe wire coil (A). [Illustration: _Fig. 15. _ DIRECTION OF CURRENT] From the foregoing, it will be understood that a wire carrying a currentof electricity not only is affected within its body, but that it alsohas a sphere of influence exteriorly to the body of the wire, at allpoints; and advantage is taken of this phenomenon in constructingmotors, dynamos, electrical measuring devices and almost every kind ofelectrical mechanism in existence. EXTERIOR MAGNETIC INFLUENCE AROUND A WIRE CARRYING A CURRENT. --Bear inmind that the wire coil (A, Fig. 14) does not come into contact with thecore (C). It is insulated from the core, either by air or by rubber orother insulating substance, and a current passing from A to C underthose conditions is a current of _induction_. On the other hand, thecurrent flowing through the wire (A) from end to end is called a_conduction_ current. Remember these terms. In this connection there is also another thing which you will do well tobear in mind. In Fig. 15 you will notice a core (C) and an insulatedwire coil (B) wound around it. The current, through the wire (B), asshown by the darts (D), moves in one direction, and the induced currentin the core (C) travels in the opposite direction, as shown by the darts(D). [Illustration: _Fig. 16. _ DIRECTION OF INDUCTION CURRENT] PARALLEL WIRES. --In like manner, if two wires (A, B, Fig. 16) areparallel with each other, and a current of electricity passes along thewire (A) in one direction, the induced current in the wire (B) will movein the opposite direction. These fundamental principles should be thoroughly understood andmastered. CHAPTER IV FRICTIONAL, VOLTAIC OR GALVANIC, AND ELECTRO-MAGNETIC ELECTRICITY THREE ELECTRICAL SOURCES. --It has been found that there are three kindsof electricity, or, to be more accurate, there are three ways togenerate it. These will now be described. When man first began experimenting, he produced a current by frictionalmeans, and collected the electricity in a bottle or jar. Electricity, sostored, could be drawn from the jar, by attaching thereto suitableconnection. This could be effected only in one way, and that was bydischarging the entire accumulation instantaneously. At that time theyknew of no means whereby the current could be made to flow from the jaras from a battery or cell. FRICTIONAL ELECTRICITY. --With a view of explaining the principlesinvolved, we show in Fig. 17 a machine for producing electricity byfriction. [Illustration: _Fig. 17. _ FRICTION-ELECTRICITY MACHINE] This is made up as follows: A represents the base, having thereon a flatmember (B), on which is mounted a pair of parallel posts or standards(C, C), which are connected at the top by a cross piece (D). Betweenthese two posts is a glass disc (E), mounted upon a shaft (F), whichpasses through the posts, this shaft having at one end a crank (G). Twoleather collecting surfaces (H, H), which are in contact with the glassdisc (E), are held in position by arms (I, J), the arm (I) beingsupported by the cross piece (D), and the arm (J) held by the base piece(B). A rod (K), U-shaped in form, passes over the structure here thusdescribed, its ends being secured to the base (B). The arms (I, J) areboth electrically connected with this rod, or conductor (K), joined to amain conductor (L), which has a terminating knob (M). On each side andclose to the terminal end of each leather collector (H) is a fork-shapedcollector (N). These two collectors are also connected electrically withthe conductor (K). When the disc is turned electricity is generated bythe leather flaps and accumulated by the collectors (N), after which itis ready to be discharged at the knob (M). In order to collect the electricity thus generated a vessel called aLeyden jar is used. LEYDEN JAR. --This is shown in Fig. 18. The jar (A) is of glass coatedexteriorly at its lower end with tinfoil (B), which extends up a littlemore than halfway from the bottom. This jar has a wooden cover or top(C), provided centrally with a hole (D). The jar is designed to receivewithin it a tripod and standard (E) of lead. Within this lead standardis fitted a metal rod (F), which projects upwardly through the hole (D), its upper end having thereon a terminal knob (G). A sliding cork (H) onthe rod (F) serves as a means to close the jar when not in use. When inuse this cork is raised so the rod may not come into contact, electrically, with the cover (C). The jar is half filled with sulphuric acid (I), after which, in orderto charge the jar, the knob (G) is brought into contact with the knob(M) of the friction generator (Fig. 17). VOLTAIC OR GALVANIC ELECTRICITY. --The second method of generatingelectricity is by chemical means, so called, because a liquid is used asone of the agents. [Illustration: _Fig. 18. _ LEYDEN JAR] Galvani, in 1790, made the experiments which led to the generation ofelectricity by means of liquids and metals. The first battery was calledthe "crown of cups, " shown in Fig. 19, and consisting of a row of glasscups (A), containing salt water. These cups were electrically connectedby means of bent metal strips (B), each strip having at one end a copperplate (C), and at the other end a zinc plate (D). The first plate in thecup at one end is connected with the last plate in the cup at the otherend by a conductor (E) to make a complete circuit. [Illustration: _Fig. 19. _ GALVANIC ELECTRICITY. CROWN OF CUPS] THE CELL AND BATTERY. --From the foregoing it will be seen that withineach cup the current flows from the zinc to the copper plates, andexteriorly from the copper to the zinc plates through the conductors (Band E). A few years afterwards Volta devised what is known as the voltaic pile(Fig. 20). VOLTAIC PILE--HOW MADE. --This is made of alternate discs of copper andzinc with a piece of cardboard of corresponding size between each zincand copper plate. The cardboard discs are moistened with acidulatedwater. The bottom disc of copper has a strip which connects with a cupof acid, and one wire terminal (A) runs therefrom. The upper disc, whichis of zinc, is also connected, by a strip, with a cup of acid from whichextends the other terminal wire (B). [Illustration: _Fig. 20. _ VOLTAIC ELECTRICITY] _Plus and Minus Signs. _--It will be noted that the positive or copperdisc has the plus sign (+) while the zinc disc has the minus (-) sign. These signs denote the positive and the negative sides of the current. The liquid in the cells, or in the moistened paper, is called the_electrolyte_ and the plates or discs are called _electrodes_. To definethem more clearly, the positive plate is the _anode_, and the negativeplate the _cathode_. The current, upon entering the zinc plate, decomposes the water in theelectrolyte, thereby forming oxygen. The hydrogen in the water, whichhas also been formed by the decomposition, is carried to the copperplate, so that the plate finally is so coated with hydrogen that it isdifficult for the current to pass through. This condition is called"polarization, " and to prevent it has been the aim of all inventors. Toit also we may attribute the great variety of primary batteries, eachhaving some distinctive claim of merit. THE COMMON PRIMARY CELL. --The most common form of primary cell containssulphuric acid, or a sulphuric acid solution, as the electrolyte, withzinc for the _anode_, and carbon, instead of copper, for the _cathode_. The ends of the zinc and copper plates are called _terminals_, and whilethe zinc is the anode or positive element, its _terminal_ is designatedas the positive pole. In like manner, the carbon is the negativeelement or cathode, and its terminal is designated as negative pole. Fig. 21 will show the relative arrangement of the parts. It is customaryto term that end or element from which the current flows as positive. Acell is regarded as a whole, and as the current passes out of the cellfrom the copper element, the copper terminal becomes positive. [Illustration: _Fig. 21. _ PRIMARY BATTERY] BATTERY RESISTANCE, ELECTROLYTE AND CURRENT. --The following should becarefully memorized: A cell has reference to a single vessel. When two or more cells arecoupled together they form a _battery_. _Resistance_ is opposition to the movement of the current. If it isoffered by the electrolyte, it is designated "Internal Resistance. " If, on the other hand, the opposition takes place, for instance, through thewire, it is then called "External Resistance. " The electrolyte must be either acid, or alkaline, or saline, and theelectrodes must be of dissimilar metals, so the electrolyte will attackone of them. The current is measured in amperes, and the force with which it iscaused to flow is measured in volts. In practice the word "current" isused to designate ampere flow; and electromotive force, or E. M. F. , isused instead of voltage. ELECTRO-MAGNETIC ELECTRICITY. --The third method of generatingelectricity is by electro-magnets. The value and use of induction willnow be seen, and you will be enabled to utilize the lesson concerningmagnetic action referred to in the previous chapter. MAGNETIC RADIATION. --You will remember that every piece of metal whichis within the path of an electric current has a space all about itssurface from end to end which is electrified. This electrified fieldextends out a certain distance from the metal, and is supposed tomaintain a movement around it. If, now, another piece of metal isbrought within range of this electric or magnetic zone and moved acrossit, so as to cut through this field, a current will be generatedthereby, or rather added to the current already exerted, so that if westart with a feeble current, it can be increased by rapidly "cutting thelines of force, " as it is called. DIFFERENT KINDS OF DYNAMO. --While there are many kinds of dynamo, theyall, without exception, are constructed in accordance with thisprinciple. There are also many varieties of current. For instance, adynamo may be made to produce a high voltage and a low amperage; anotherwith high amperage and low voltage; another which gives a direct currentfor lighting, heating, power, and electroplating; still another whichgenerates an alternating current for high tension power, ortransmission, arc-lighting, etc. , all of which will be explainedhereafter. In this place, however, a full description of a direct-current dynamowill explain the principle involved in all dynamos--that to generate acurrent of electricity makes it necessary for us to move a field offorce, like an armature, rapidly and continuously through another fieldof force, like a magnetic field. DIRECT-CURRENT DYNAMO. --We shall now make the simplest form of dynamo, using for this purpose a pair of permanent magnets. [Illustration: _Fig. 22. _ DYNAMO FIELD AND POLE PIECE] SIMPLE MAGNET CONSTRUCTION. --A simple way to make a pair of magnets forthis purpose is shown in Fig. 22. A piece of round 3/4-inch steel core(A), 5-1/2 inches long, is threaded at both ends to receive at one end anut (B), which is screwed on a sufficient distance so that the end ofthe core (A) projects a half inch beyond the nut. The other end of thesteel core has a pole piece of iron (C) 2" × 2" × 4", with a holemidway between the ends, threaded entirely through, and provided alongone side with a concave channel, within which the armature is to turn. Now, before the pole piece (C) is put on, we will slip on a disc (E), made of hard rubber, then a thin rubber tube (F), and finally a rubberdisc (G), so as to provide a positive insulation for the wire coil whichis wound on the bobbin thus made. HOW TO WIND. --In practice, and as you go further along in this work, youwill learn the value, first, of winding one layer of insulated wire onthe spool, coating it with shellac, and then putting on the next layer, and so on; when completely wound, the two wire terminals may be broughtout at one end; but for our present purpose, and to render theexplanation clearer, the wire terminals are at the opposite ends of thespool (H, H'). THE DYNAMO FIELDS. --Two of these spools are so made and they are calledthe _fields_ of the dynamo. We will next prepare an iron bar (I), 5 inches long and 1/2 inch thickand 1-1/2 inches wide, then bore two holes through it so the distancemeasures 3 inches from center to center. These holes are to be threadedfor the 3/4-inch cores (A). This bar holds together the upper ends ofthe cores, as shown in Fig. 23. [Illustration: _Fig. 23. _ BASE AND FIELDS ASSEMBLED] We then prepare a base (J) of any hard wood, 2 inches thick, 8 incheslong and 8 inches wide, and bore two 3/4-inch holes 3 inches apart on amiddle line, to receive a pair of 3/4-inch cap screws (K), which passupwardly through the holes in the base and screw into the pole pieces(C). A wooden bar (L), 1-1/2" × 1-1/2", 8 inches long, is placed undereach pole piece, which is also provided with holes for the cap screws(K). The lower side of the base (J) should be countersunk, as at M, sothe head of the nut will not project. The fields of the dynamo are nowsecured in position to the base. [Illustration: _Fig. 24. _ DETAILS OF THE ARMATURE, CORE _Fig. 25. _ DETAILS OF THE ARMATURE, BODY] THE ARMATURE. --A bar of iron (Fig. 24), 1" × 1" and 2-1/4 inches long, is next provided. Through this bar (1) are then bored two 5/16-inchholes 1-3/4 inches apart, and on the opposite sides of this bar are twohalf-rounded plates of iron (3) (Fig. 25). ARMATURE WINDING. --Each plate is 1/2 inch thick, 1-3/4 inches wide and 4inches long, each plate having holes (4) to coincide with the holes (2)of the bar (1), so that when the two plates are applied to oppositesides of the bar, and riveted together, a cylindrical member is formed, with two channels running longitudinally, and transversely at the ends;and in these channels the insulated wires are wound from end to endaround the central block (1). MOUNTING THE ARMATURE. --It is now necessary to provide a means forrevolving this armature. To this end a brass disc (5, Fig. 26) is made, 2 inches in diameter, 1/8 inch thick. Centrally, at one side, is aprojecting stem (6) of round brass, which projects out 2 inches, and theouter end is turned down, as at 7, to form a small bearing surface. [Illustration: _Fig. 26. _ JOURNALS _Fig. 27. _ COMMUTATOR, ARMATURE MOUNTINGS] The other end of the armature has a similar disc (8), with a centralstem (9), 1-1/2 inches long, turned down to 1/4-inch diameter up towithin 1/4 inch of the disc (7), so as to form a shoulder. THE COMMUTATOR. --In Fig. 27 is shown, at 10, a wooden cylinder, 1 inchlong and 1-1/4 inches in diameter, with a hole (11) bored throughaxially, so that it will fit tightly on the stem (6) of the disc (5). Onthis wooden cylinder is driven a brass or copper tube (12), which hasholes (13) opposite each other. Screws are used to hold the tube to thewooden cylinder, and after they are properly secured together, the tube(12) is cut by a saw, as at 14, so as to form two independent tubularsurfaces. [Illustration: _Fig. 28. _ END VIEW ARMATURE, MOUNTED] These tubular sections are called the commutator plates. [Illustration: _Fig. 29. _ TOP VIEW OF ARMATURE ON BASE] In order to mount this armature, two bearings are provided, eachcomprising a bar of brass (15, Fig. 28), each 1/4 inch thick, 1/2 inchwide and 4-1/2 inches long. Two holes, 3 inches apart, are formedthrough this bar, to receive round-headed wood screws (16), these screwsbeing 3 inches long, so they will pass through the wooden pieces (I)and enter the base (J). Midway between the ends, each bar (15) has aniron bearing block (17), 3/4" × 1/2" and 1-1/2 inches high, the 1/4-inchhole for the journal (7) being midway between its ends. COMMUTATOR BRUSHES. --Fig. 28 shows the base, armature and commutatorassembled in position, and to these parts have been added the commutatorbrushes. The brush holder (18) is a horizontal bar made of hard rubberloosely mounted upon the journal pin (7), which is 2-1/2 inches long. Ateach end is a right-angled metal arm (19) secured to the bar (18) byscrews (20). To these arms the brushes (21) are attached, so that theirspring ends engage with the commutator (12). An adjusting screw (22) inthe bearing post (17), with the head thereof bearing against thebrush-holder (18), serves as a means for revolubly adjusting the brusheswith relation to the commutator. DYNAMO WINDINGS. --There are several ways to wind the dynamos. Thesecan be shown better by the following diagrams (Figs. 30, 31, 32, 33): THE FIELD. --If the field (A, Fig. 30) is not a permanent magnet, it mustbe excited by a cell or battery, and the wires (B, B') are connected upwith a battery, while the wires (C, C') may be connected up to run amotor. This would, therefore, be what is called a "separately excited"dynamo. In this case the battery excites the field and the armature(D), cutting the lines of force at the pole pieces (E), so that thearmature gathers the current for the wires (C, C'). [Illustration: _Fig. 30. _ FIELD WINDING] [Illustration: _Fig. 31. _ SERIES-WOUND] SERIES-WOUND FIELD. --Fig. 31 shows a "series-wound" dynamo. The wires ofthe fields (A) are connected up in series with the brushes of thearmature (D), and the wires (G, G') are led out and connected up with alamp, motor or other mechanism. In this case, as well as in Figs. 32 and33, both the field and the armature are made of soft gray iron. Withthis winding and means of connecting the wires, the field is constantlyexcited by the current passing through the wires. SHUNT-WOUND FIELD. --Fig. 32 represents what is known as a "shunt-wound"dynamo. Here the field wires (H, H) connect with the opposite brushesof the armature, and the wires (I, I') are also connected with thebrushes, these two wires being provided to perform the work required. This is a more useful form of winding for electroplating purposes. [Illustration: _Fig. 32. _ SHUNT-WOUND _Fig. 32. _ COMPOUND-WOUND] COMPOUND-WOUND FIELD. --Fig. 33 is a diagram of a "compound-wound"dynamo. The regular field winding (J) has its opposite ends connecteddirectly with the armature brushes. There is also a winding, of acomparatively few turns, of a thicker wire, one terminal (K) of which isconnected with one of the brushes and the other terminal (K') forms oneside of the lighting circuit. A wire (L) connects with the otherarmature brush to form a complete lighting circuit. CHAPTER V HOW TO DETECT AND MEASURE ELECTRICITY MEASURING INSTRUMENTS. --The production of an electric current would notbe of much value unless we had some way by which we might detect andmeasure it. The pound weight, the foot rule and the quart measure arevery simple devices, but without them very little business could bedone. There must be a standard of measurement in electricity as well asin dealing with iron or vegetables or fabrics. As electricity cannot be seen by the human eye, some mechanism must bemade which will reveal its movements. THE DETECTOR. --It has been shown in the preceding chapter that a currentof electricity passing through a wire will cause a current to passthrough a parallel wire, if the two wires are placed close together, butnot actually in contact with each other. An instrument which revealsthis condition is called a _galvanometer_. It not only detects thepresence of a current, but it shows the direction of its flow. We shallnow see how this is done. For example, the wire (A, Fig. 35) is connected up in an electriccircuit with a permanent magnet (B) suspended by a fine wire (C), sothat the magnet (B) may freely revolve. [Illustration: _Fig. 34. _ _Fig. 35. _ _Fig. 36. _ TO THE RIGHT, COMPASS MAGNET, TO THE LEFT] For convenience, the magnetic field is shown flowing in the direction ofthe darts, in which the dart (D) represents the current within themagnet (B) flowing toward the north pole, and the darts (E) showing theexterior current flowing toward the south pole. Now, if the wire (A) isbrought up close to the magnet (B), and a current passed through A, themagnet (B) will be affected. Fig. 35 shows the normal condition of themagnetized bar (B) parallel with the wire (A) when a current is notpassing through the latter. DIRECTION OF CURRENT. --If the current should go through the wire (A)from right to left, as shown in Fig. 34, the magnet (B) would swing inthe direction taken by the hands of a clock and assume the positionshown in Fig. 34. If, on the other hand, the current in the wire (A)should be reversed or flow from left to right, the magnet (B) wouldswing counter-clock-wise, and assume the position shown in Fig. 36. Thelittle pointer (G) would, in either case, point in the direction of theflow of the current through the wire (A). [Illustration: _Fig. 37. _ INDICATING DIRECTION OF CURRENT] SIMPLE CURRENT DETECTOR. --A simple current detector may be made asfollows: Prepare a base 3' × 4' in size and 1 inch thick. At each corner of oneend fix a binding post, as at A, A', Fig. 37. Then select 20 feet of No. 28 cotton-insulated wire, and make a coil (B) 2 inches in diameter, leaving the ends free, so they may be affixed to the binding posts (A, A'). Now glue or nail six blocks (C) to the base, each block being 1" ×1" × 2", and lay the coil on these blocks. Then drive an L-shaped nail(D) down into each block, on the inside of the coil, as shown, so as tohold the latter in place. [Illustration: _Fig. 38. _ THE BRIDGE] Now make a bridge (E, Fig. 38) of a strip of brass 1/2 inch wide, 1/16inch thick and long enough to span the coil, and bend the ends down, asat F, so as to form legs. A screw hole (G) is formed in each foot, so itmay be screwed to the base. Midway between the ends this bridge has a transverse slot (H) in oneedge, to receive therein the pivot pin of the swinging magnet. In orderto hold the pivot pin in place, cut out an H-shaped piece of sheet brass(I), which, when laid on the bridge, has its ends bent around thelatter, as shown at J, and the crossbar of the H-shaped piece then willprevent the pivot pin from coming out of the slot (H). [Illustration: _Fig. 39. _ DETAILS OF DETECTOR] The magnet is made of a bar of steel (K, Fig. 39) 1-1/2 inches long, 3/8inch wide and 1/16 inch thick, a piece of a clock spring being veryserviceable for this purpose. The pivot pin is made of an ordinary pin(L), and as it is difficult to solder the steel magnet (K) to the pin, solder only a small disc (M) to the pin (L). Then bore a hole (N)through the middle of the magnet (K), larger in diameter than the pin(L), and, after putting the pin in the hole, pour sealing wax into thehole, and thereby secure the two parts together. Near the upper end ofthe pin (L) solder the end of a pointer (O), this pointer being at rightangles to the armature (K). It is better to have a metal socket for thelower end of the pin. When these parts are put together, as shown inFig. 37, a removable glass top, or cover, should be provided. This is shown in Fig. 40, in which a square, wooden frame (P) is used, and a glass (Q) fitted into the frame, the glass being so arranged thatwhen the cover is in position it will be in close proximity to the upperprojecting end of the pivot pin (L), and thus prevent the magnet frombecoming misplaced. [Illustration: _Fig. 40. _ CROSS SECTION OF DETECTOR] HOW TO PLACE THE DETECTOR. --If the detector is placed north and south, as shown by the two markings, N and S (Fig. 37), the magnet bar willpoint north and south, being affected by the earth's magnetism; but whena current of electricity flows through the coil (B), the magnet will bedeflected to the right or to the left, so that the pointer (O) will thenshow the direction in which the current is flowing through the wire (R)which you are testing. The next step of importance is to _measure_ the current, that is, todetermine its strength or intensity, as well as the flow or quantity. DIFFERENT WAYS OF MEASURING A CURRENT. --There are several ways tomeasure the properties of a current, which may be defined as follows: 1. THE SULPHURIC ACID VOLTAMETER. --By means of an electrolytic action, whereby the current decomposes an acidulated solution--that is, waterwhich has in it a small amount of sulphuric acid--and then measuring thegas generated by the current. 2. THE COPPER VOLTAMETER. --By electro-chemical means, in which thecurrent passes through plates immersed in a solution of copper sulphate. 3. THE GALVANOSCOPE. --By having a coil of insulated wire, with a magnetsuspended so as to turn freely within the coil, forming what is called agalvanoscope. 4. ELECTRO-MAGNETIC METHOD. --By using a pair of magnets and sending acurrent through the coils, and then measuring the pull on the armature. 5. THE POWER OR SPEED METHOD. --By using an electric fan, and noting therevolutions produced by the current. 6. THE CALORIMETER. --By using a coil of bare wire, immersed in paraffineoil, and then measuring the temperature by means of a thermometer. [Illustration: _Fig. 41. _ ACID VOLTAMETER] [Illustration: _Fig. 42. _ COPPER VOLTAMETER] 7. THE LIGHT METHOD. --Lastly, by means of an electric light, whichshows, by its brightness, a greater or less current. THE PREFERRED METHODS. --It has been found that the first and secondmethods are the only ones which will accurately register currentstrength, and these methods have this advantage--that the chemicaleffect produced is not dependent upon the size or shape of the apparatusor the plates used. HOW TO MAKE A SULPHURIC ACID VOLTAMETER. --In Fig. 41 is shown a simpleform of sulphuric acid voltameter, to illustrate the first method. A isa jar, tightly closed by a cover (B). Within is a pair of platinumplates (C, C), each having a wire (D) through the cover. The cover has avertical glass tube (E) through it, which extends down to the bottom ofthe jar, the electrolyte therein being a weak solution of sulphuricacid. When a current passes through the wires (D), the solution ispartially decomposed--that is, converted into gas, which passes up intothe vacant space (F) above the liquid, and, as it cannot escape, itpresses the liquid downwardly, and causes the latter to flow upwardlyinto the tube (E). It is then an easy matter, after the current is onfor a certain time, to determine its strength by the height of theliquid in the tube. HOW TO MAKE A COPPER VOLTAMETER. --The second, or copper voltameter, isshown in Fig. 42. The glass jar (A) contains a solution of coppersulphate, known in commerce as blue vitriol. A pair of copper plates(B, B') are placed in this solution, each being provided with aconnecting wire (C). When a current passes through the wires (C), onecopper plate (B) is eaten away and deposited on the other plate (B'). Itis then an easy matter to take out the plates and find out how much inweight B' has gained, or how much B has lost. In this way, in comparing the strength of, say, two separate currents, one should have each current pass through the voltameter the same lengthof time as the other, so as to obtain comparative results. It is not necessary, in the first and second methods, to consider theshapes, the sizes of the plates or the distances between them. In thefirst method the gas produced, within a given time, will be the same, and in the second method the amount deposited or eaten away will be thesame under all conditions. DISADVANTAGES OF THE GALVANOSCOPE. --With the third method (using thegalvanoscope) it is necessary, in order to get a positively correctreading instrument, to follow an absolutely accurate plan inconstructing each part, in every detail, and great care must beexercised, particularly in winding. It is necessary also to be verycareful in selecting the sizes of wire used and in the number of turnsmade in the coils. This is equally true of the fourth method, using the electro-magnet, because the magnetic pull is dependent upon the size of wire from whichthe coils are made and the number of turns of wire. OBJECTIONS TO THE CALORIMETER. --The calorimeter, or sixth method, hasthe same objection. The galvanoscope and electro-magnet do not respondequally to all currents, and this is also true, even to a greaterextent, with the calorimeter. CHAPTER VI VOLTS, AMPERES, OHMS AND WATTS UNDERSTANDING TERMS. --We must now try to ascertain the meaning of someof the terms so frequently used in connection with electricity. If youintended to sell or measure produce or goods of any kind, it would beessential to know how many pints or quarts are contained in a gallon, orin a bushel, or how many inches there are in a yard, and you also oughtto know just what the quantity term _bushel_ or the measurement _yard_means. INTENSITY AND QUANTITY. --Electricity, while it has no weight, is capableof being measured by means of its intensity, or by its quantity. Lightmay be measured or tested by its brilliancy. If one light is of lessintensity than another and both of them receive their impulses from thesame source, there must be something which interferes with that lightwhich shows the least brilliancy. Electricity can also be interferedwith, and this interference is called _resistance_. VOLTAGE. --Water may be made to flow with greater or less force, orvelocity, through a pipe, the degree of same depending upon the heightof the water which supplies the pipe. So with electricity. It may passover a wire with greater or less force under one condition than another. This force is called voltage. If we have a large pipe, a much greaterquantity of water will flow through it than will pass through a smallpipe, providing the pressure in each case is alike. This quantity inelectricity is called _amperage_. In the case of water, a column 1" × 1", 28 inches in height, weighs 1pound; so that if a pipe 1 inch square draws water from the bottom itflows with a pressure of 1 pound. If the pipe has a measurement of 2square inches, double the quantity of water will flow therefrom, at thesame pressure. AMPERAGE. --If, on the other hand, we have a pipe 1 inch square, andthere is a depth of 56 inches of water in the reservoir, we shall get asmuch water from the reservoir as though we had a pipe of 2 square inchesdrawing water from a reservoir which is 28 inches deep. MEANING OF WATTS. --It is obvious, therefore, that if we multiply theheight of the water in inches with the area of the pipe, we shall obtaina factor which will show how much water is flowing. Here are two examples: 1. 28 inches = height of the water in the reservoir. 2 square inches = size of the pipe. Multiply 28 × 2 = 56. 2. 56 = height of the water in the reservoir. 1 square inch = size of the pipe. Multiply 56 × 1 = 56. Thus the two problems are equal. A KILOWATT. --Now, in electricity, remembering that the height of thewater corresponds with _voltage_ in electricity, and the size of thepipe with _amperage_, if we multiply volts by amperes, or amperes byvolts, we get a result which is indicated by the term _watts_. Onethousand of these watts make a kilowatt, and the latter is the standardof measurement by which a dynamo or motor is judged or rated. Thus, if we have 5 amperes and 110 volts, the result of multiplying themwould be 550 watts, or 5 volts and 110 amperes would produce 550 watts. A STANDARD OF MEASUREMENT. --But with all this we must have somestandard. A bushel measure is of a certain size, and a foot has adefinite length, so in electricity there is a recognized force andquantity which are determined as follows: THE AMPERE STANDARD. --It is necessary, first, to determine what anampere is. For this purpose a standard solution of nitrate of silver isused, and a current of electricity is passed through this solution. Indoing so the current deposits silver at the rate of 0. 001118 grains persecond for each ampere. THE VOLTAGE STANDARD. --In order to determine the voltage we must knowsomething of _resistance_. Different metals do not transmit a currentwith equal ease. The size of a conductor, also, is an important factorin the passage of a current. A large conductor will transmit a currentmuch better than a small conductor. We must therefore have a standardfor the _ohm_, which is the measure of resistance. THE OHM. --It is calculated in this way: There are several standards, butthe one most generally employed is the _International Ohm_. To determineit, by this system, a column of pure mercury, 106. 3 millimeters long andweighing 14. 4521 grams, is used. This would make a square tube about 94inches long, and a little over 1/25 of an inch in diameter. Theresistance to a current flow in such a column would be equal to 1 ohm. CALCULATING THE VOLTAGE. --In order to arrive at the voltage we must usea conductor, which, with a resistance of 1 ohm, will produce 1 ampere. It must be remembered that the volt is the practical unit ofelectro-motive force. While it would be difficult for the boy to conduct these experiments inthe absence of suitable apparatus, still, it is well to understandthoroughly how and why these standards are made and used. CHAPTER VII PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS ANDLIKE APPARATUS SIMPLE SWITCHES. --We have now gone over the simpler or elementaryoutlines of electrical phenomena, and we may commence to do some of thepractical work in the art. We need certain apparatus to makeconnections, which will be constructed first. A TWO-POLE SWITCH. --A simple two-pole switch for a single line is madeas follows: A base block (A, Fig. 43) 3 inches long, 2 inches wide and 3/4 inchthick, has on it, at one end, a binding screw (B), which holds a pair offingers (C) of brass or copper, these fingers being bent upwardly and soarranged as to serve as fingers to hold a switch bar (D) between them. This bar is also of copper or brass and is pivoted to the fingers. Nearthe other end of the base is a similar binding screw (E) and fingers (F)to receive the blade of the switch bar. The bar has a handle (G) ofwood. The wires are attached to the respective binding screws (B, E). DOUBLE-POLE SWITCH. --A double-pole switch or a switch for a double lineis shown in Fig. 44. This is made similar in all respects to the oneshown in Fig. 43, excepting that there are two switch blades (A, A)connected by a cross bar (B) of insulating material, and this barcarries the handle (C). [Illustration: _Fig. 43. _ TWO-POLE SWITCH] [Illustration: _Fig. 44. _ DOUBLE-POLE SWITCH] Other types of switch will be found very useful. In Fig. 45 is a simplesliding switch in which the base block has, at one end, a pair of copperplates (A, B), each held at one end to the base by a binding screw (C), and having a bearing or contact surface (D) at its other end. At theother end of the base is a copper plate (E) held by a binding screw (F), to the inner end of which plate is hinged a swinging switch blade (G), the free end of which is adapted to engage with the plates (A, B). [Illustration: _Fig. 45. _ SLIDING SWITCH] SLIDING SWITCH. --This sliding switch form may have the contact plates(A, B and C, Fig. 46) circularly arranged and any number may be locatedon the base, so they may be engaged by a single switching lever (H). Itis the form usually adopted for rheostats. REVERSING SWITCH. --A reversing switch is shown in Fig. 47. The base hastwo plates (A, B) at one end, to which the parallel switch bars (C, D)are hinged. The other end of the base has three contact plates (E, F, G)to engage the swinging switch bars, these latter being at such distanceapart that they will engage with the middle and one of the outer plates. The inlet wires, positive and negative, are attached to the plates (A, B, respectively), and one of the outlet wires (H) is attached to themiddle contact plate (F), while the other wire is connected up with bothof the outside plates. When the switch bars (C, D) are thrown to theleft so as to be in contact with E, F, the outside plate (E) and themiddle plate (F) will be positive and negative, respectively; but whenthe switch is thrown to the right, as shown in the figure, plate Fbecomes positive and plate E negative, as shown. [Illustration: _Fig. 46. _ RHEOSTAT FORM OF SWITCH] PUSH BUTTONS. --A push button is but a modified structure of a switch, and they are serviceable because they are operating, or the circuit isformed only while the finger is on the button. [Illustration: _Fig. 47. _ REVERSING SWITCH] In its simplest form (Fig. 48) the push button has merely a circularbase (A) of insulating material, and near one margin, on the flat side, is a rectangular plate (B), intended to serve as a contact plate as wellas a means for attaching one of the wires thereto. In line with thisplate is a spring finger (C), bent upwardly so that it is normally outof contact with the plate (B), its end being held by a binding screw(D). To effect contact, the spring end of the finger (C) is pressedagainst the bar (B), as at E. This is enclosed in a suitable casing, such as will readily suggest itself to the novice. ELECTRIC BELL. --One of the first things the boy wants to make, and onewhich is also an interesting piece of work, is an electric bell. To make this he will be brought, experimentally, in touch with severalimportant features in electrical work. He must make a battery for theproduction of current, a pair of electro-magnets to be acted upon by thecurrent, a switch to control it, and, finally, he must learn how toconnect it up so that it may be operated not only from one, but from twoor more push buttons. [Illustration: _Fig. 48. _ PUSH BUTTON] HOW MADE. --In Fig. 49 is shown an electric bell, as usually constructed, so modified as to show the structure at a glance, with its connections. A is the base, B, B' the binding posts for the wires, C, C theelectro-magnets, C' the bracket for holding the magnets, D the armature, E the thin spring which connects the armature with the post F, G theclapper arm, H the bell, I the adjusting screw on the post J, K the wirelead from the binding post B to the first magnet, L the wire whichconnects the two magnets, M the wire which runs from the second magnetto the post J, and N a wire leading from the armature post to thebinding post B'. [Illustration: _Fig. 49. _ ELECTRIC BELL] The principle of the electric bell is this: In looking at Fig. 49, youwill note that the armature bar D is held against the end of theadjusting screw by the small spring E. When a current is turned on, itpasses through the connections and conduits as follows: Wire K to themagnets, wire M to the binding post J, and set screw I, then through thearmature to the post F, and from post F to the binding post B'. [Illustration: _Fig. 50. _ ARMATURE OF ELECTRIC BELL] ELECTRIC BELL--HOW OPERATED. --The moment a current passes through themagnets (C, C), the core is magnetized, and the result is that thearmature (D) is attracted to the magnets, as shown by the dotted lines(O), when the clapper strikes the bell. But when the armature moves overto the magnet, the connection is broken between the screw (I) andarmature (D), so that the cores of the magnets are demagnetized and losetheir pull, and the spring (E) succeeds in drawing back the armature. This operation of vibrating the armature is repeated with greatrapidity, alternately breaking and re-establishing the circuit, by theaction of the current. In making the bell, you must observe one thing, the binding posts (B, B') must be insulated from each other, and the post J, or the post F, should also be insulated from the base. For convenience we show the postF insulated, so as to necessitate the use of wire (N) from post (F) tobinding post (B'). The foregoing assumes that you have used a cast metal base, as mostbells are now made; but if you use a wooden base, the binding posts (B, B') and the posts (F, J) are insulated from each other, and theconstruction is much simplified. It is better, in practice, to have a small spring (P, Fig. 50) betweenthe armature (D) and the end of the adjusting screw (I), so as to give areturn impetus to the clapper. The object of the adjusting screw is topush and hold the armature close up to the ends of the magnets, if itseems necessary. If two bells are placed on the base with the clapper mounted betweenthem, both bells will be struck by the swinging motion of the armature. An easily removable cap or cover is usually placed over the coils andarmature, to keep out dust. A very simple annunciator may be attached to the bell, as shown in thefollowing figures: [Illustration: _Figs. 51-54. _ ANNUNCIATOR] ANNUNCIATORS. --Make a box of wood, with a base (A) 4" × 5" and 1/2 inchthick. On this you can permanently mount the two side pieces (B) and twotop and bottom pieces (C), respectively, so they project outwardly4-1/2 inches from the base. On the open front place a wood or metalplate (D), provided with a square opening (D), as in Fig. 54, near itslower end. This plate is held to the box by screws (E). Within is a magnet (F), screwed into the base (A), as shown in Fig. 51;and pivoted to the bottom of the box is a vertical armature (G), whichextends upwardly and contacts with the core of the magnet. The upper endof the armature has a shoulder (H), which is in such position that itserves as a rest for a V-shaped stirrup (I), which is hinged at J to thebase (C). This stirrup carries the number plate (K), and when it israised to its highest point it is held on the shoulder (H), unless theelectro-magnet draws the armature out of range of the stirrup. A spring(L) bearing against the inner side of the armature keeps its upper endnormally away from the magnet core. When the magnet draws the armatureinwardly, the number plate drops and exposes the numeral through theopening in the front of the box. In order to return the number plate toits original position, as shown in Fig. 51, a vertical trigger (M)passes up through the bottom, its upper end being within range of one ofthe limbs of the stirrup. This is easily made by the ingenious boy, and will be quite anacquisition to his stock of instruments. In practice, the annunciatormay be located in any convenient place and wires run to that point. [Illustration: _Fig. 55. _ ALARM SWITCH ON WINDOW] [Illustration: _Fig. 56. _ BURGLAR ALARM ATTACHMENT TO WINDOW] BURGLAR ALARM. --In order to make a burglar alarm connection with a bell, push buttons or switches may be put in circuit to connect with thewindows and doors, and by means of the annunciators you may locate thedoor or window which has been opened. The simplest form of switch for awindow is shown in the following figures: The base piece (A), which may be of hard rubber or fiber, is 1/4 inchthick and 1" × 1-1/2" in size. [Illustration: _Fig. 57. _ BURGLAR ALARM CONTACT] At one end is a brass plate (B), with a hole for a wood screw (C), thisscrew being designed to pass through the plate and also into thewindow-frame, so as to serve as a means of attaching one of the wiresthereto. The inner end of the plate has a hole for a round-headed screw(C') that also goes through the base and into the window-frame. It alsopasses through the lower end of the heart-shaped metal switch-piece(D). The upper end of the base has a brass plate (E), also secured to thebase and window by a screw (F) at its upper end. The heart-shaped switchis of such length and width at its upper end that when it is swung tothe right with one of the lobes projecting past the edge of thewindow-frame, the other lobe will be out of contact with the plate (E). [Illustration: _Fig. 58. _ NEUTRAL POSITION OF CONTACT] The window sash (G) has a removable pin (H), which, when the sash movesupwardly, is in the path of the lobe of the heart-shaped switch, asshown in Fig. 56, and in this manner the pin (H) moves the upper end ofthe switch (D) inwardly, so that the other lobe contacts with the plate(E), and establishes an electric circuit, as shown in Fig. 57. Duringthe daytime the pin (H) may be removed, and in order to protect theswitch the heart-shaped piece (D) is swung inwardly, as shown in Fig. 58, so that neither of the lobes is in contact with the plate (E). WIRE CIRCUITING. --For the purpose of understanding fully the circuiting, diagrams will be shown of the simple electric bell with two pushbuttons; next in order, the circuiting with an annunciator and then thecircuiting necessary for a series of windows and doors, with annunciatorattachments. [Illustration: _Fig. 59. _ CIRCUITING FOR ELECTRIC BELL] CIRCUITING SYSTEM WITH A BELL AND TWO PUSH BUTTONS. --Fig. 59 shows asimple circuiting system which has two push buttons, although any numbermay be used, so that the bell will ring when the circuit is closed byeither button. THE PUSH BUTTONS AND THE ANNUNCIATOR BELLS. --Fig. 60 shows three pushbuttons and an annunciator for each button. These three circuits areindicated by A, B and C, so that when either button makes contact, acomplete circuit is formed through the corresponding annunciator. [Illustration: _Fig. 60. _ _Annunciators_] [Illustration: _Fig. 61. _ WIRING SYSTEM FOR A HOUSE] WIRING UP A HOUSE. --The system of wiring up a house so that all doorsand windows will be connected to form a burglar alarm outfit, is shownin Fig. 61. It will be understood that, in practice, the bell is mountedon or at the annunciator, and that, for convenience, the annunciatorbox has also a receptacle for the battery. The circuiting is showndiagramatically, as it is called, so as fully to explain how the linesare run. Two windows and a door are connected up with an annunciatorhaving three drops, or numbers 1, 2, 3. The circuit runs from one poleof the battery to the bell and then to one post of the annunciator. Fromthe other post a wire runs to one terminal of the switch at the door orwindow. The other switch terminal has a wire running to the other poleof the battery. A, B, C represent the circuit wires from the terminals of the window anddoor switches, to the annunciators. It is entirely immaterial which side of the battery is connected up withthe bell. From the foregoing it will readily be understood how to connect up anyordinary apparatus, remembering that in all cases the magnet must bebrought into the electric circuit. CHAPTER VIII ACCUMULATORS. STORAGE OR SECONDARY BATTERIES STORING UP ELECTRICITY. --In the foregoing chapters we have seen that, originally, electricity was confined in a bottle, called the Leyden jar, from which it was wholly discharged at a single impulse, as soon as itwas connected up by external means. Later the primary battery and thedynamo were invented to generate a constant current, and after thesecame the second form of storing electricity, called the storage orsecondary battery, and later still recognized as accumulators. THE ACCUMULATOR. --The term _accumulator_ is, strictly speaking, the morenearly correct, as electricity is, in reality, "_stored_" in anaccumulator. But when an accumulator is charged by a current ofelectricity, a chemical change is gradually produced in the activeelement of which the accumulator is made. This change or decompositioncontinues so long as the charging current is on. When the accumulator isdisconnected from the charging battery or dynamo, and its terminals areconnected up with a lighting system, or with a motor, for instance, areverse process is set up, or the particles re-form themselves intotheir original compositions, which causes a current to flow in adirection opposite to that of the charging current. It is immaterial to the purposes of this chapter, as to the chargingsource, whether it be by batteries or dynamos; the same principles willapply in either case. [Illustration: _Fig. 62. _ ACCUMULATOR GRIDS] ACCUMULATOR PLATES. --The elements used for accumulator plates are redlead for the positive plates, and precipitated lead, or the well-knownlitharge, for the negative plates. Experience has shown that the bestway to hold this material is by means of lead grids. Fig. 62 shows the typical form of one of these grids. It is made oflead, cast or molded in one piece, usually square, as at A, with a wingor projection (B), at one margin, extending upwardly and provided with ahole (C). The grid is about a quarter of an inch thick. THE GRID. --The open space, called the grid, proper, comprises crossbars, integral with the plate, made in a variety of shapes. Fig. 62shows three forms of constructing these bars or ribs, the object beingto provide a form which will hold in the lead paste, which is pressed inso as to make a solid-looking plate when completed. THE POSITIVE PLATE. --The positive plate is made in the following manner:Make a stiff paste of red lead and sulphuric acid; using a solution, say, of one part of acid to two parts of water. The grid is laid on aflat surface and the paste forced into the perforations with a stiffknife or spatula. Turn over the grid so as to get the paste in evenly onboth sides. The grid is then stood on its edge, from 18 to 20 hours, to dry, andafterwards immersed in a concentrated solution of chloride of lime, soas to convert it into lead peroxide. When the action is complete it isthoroughly rinsed in cold water, and is ready to use. THE NEGATIVE PLATE. --The negative plate is filled, in like manner, withprecipitated lead. This lead is made by putting a strip of zinc into astandard solution of acetate of lead, and crystals will then form on thezinc. These will be very thin, and will adhere together, firmly, forminga porous mass. This, when saturated and kept under water for a shorttime, may be put into the openings of the negative plate. [Illustration: _Fig. 63. _ ASSEMBLAGE OF ACCUMULATOR PLATES] CONNECTING UP THE PLATES. --The next step is to put these plates inposition to form a battery. In Fig. 63 is shown a collection of platesconnected together. For simplicity in illustrating, the cell is made up of glass, porcelain, or hard rubber, with five plates (A), A, A representing the negative andB, B the positive plates. A base of grooved strips (C, C) is placed inthe batteries of the cell to receive the lower ends of the plates. Thepositive plates are held apart by means of a short section of tubing(D), which is clamped and held within the plates by a bolt (E), thisbolt also being designed to hold the terminal strip (F). In like manner, the negative plates are held apart by the two tubularsections (G), each of which is of the same length as the section D ofthe positives. The bolt (H) holds the negatives together as well as theterminal (I). The terminals should be lead strips, and it would be well, owing to the acid fumes which are formed, to coat all brass work, screws, etc. , with paraffine wax. The electrolyte or acid used in the cell, for working purposes, is apure sulphuric acid, which should be diluted with about four times itsweight in water. Remember, you should always add the strong acid to thewater, and never pour the water into the acid, as the latter methodcauses a dangerous ebullition, and does not produce a good mixture. Put enough of this solution into the cell to cover the tops of theplates, and the cell is ready. [Illustration: _Fig. 64. _ CONNECTING UP STORAGE BATTERY IN SERIES] CHARGING THE CELLS. --The charge of the current must never be less than2. 5 volts. Each cell has an output, in voltage, of about 2 volts, henceif we have, say, 10 cells, we must have at least 25 volts chargingcapacity. We may arrange these in one line, or in series, as it iscalled, so far as the connections are concerned, and charge them with adynamo, or other electrical source, which shows a pressure of 25 volts, as illustrated in Fig. 64, or, instead of this, we may put them into twoparallel sets of 5 cells each, as shown in Fig. 65, and use 12. 5 voltsto charge with. In this case it will take double the time because we arecharging with only one-half the voltage used in the first case. The positive pole of the dynamo should be connected with the positivepole of the accumulator cell, and negative with negative. When this hasbeen done run up the machine until it slightly exceeds the voltage ofthe cells. Thus, if we have 50 cells in parallel, like in Fig. 64, atleast 125 volts will be required, and the excess necessary should bringup the voltage in the dynamo to 135 or 140 volts. [Illustration: _Fig. 65. _ PARALLEL SERIES] [Illustration: _Fig. 66. _ CHARGING CIRCUIT] THE INITIAL CHARGE. --It is usual initially to charge the battery fromperiods ranging from 36 to 40 hours, and to let it stand for 12 or 15hours, after which to re-charge, until the positive plates have turnedto a chocolate color, and the negative plates to a slate or gray color, and both plates give off large bubbles of gas. In charging, the temperature of the electrolyte should not exceed 100°Fahrenheit. When using the accumulators they should never be fully discharged. THE CHARGING CIRCUIT. --The diagram (Fig. 66) shows how a chargingcircuit is formed. The lamps are connected up in parallel, asillustrated. Each 16-candle-power 105-volt lamp will carry 1/2 ampere, so that, supposing we have a dynamo which gives 110 volts, and we wantto charge a 4-volt accumulator, there will be 5-volt surplus to go tothe accumulator. If, for instance, you want the cell to have a charge of2 amperes, four of these lamps should be connected up in parallel. If 3amperes are required, use 6 lamps, and so on. CHAPTER IX THE TELEGRAPH The telegraph is a very simple instrument. The key is nothing more orless than a switch which turns the current on and off alternately. The signals sent over the wires are simply the audible sounds made bythe armature, as it moves to and from the magnets. MECHANISM IN TELEGRAPH CIRCUITS. --A telegraph circuit requires threepieces of mechanism at each station, namely, a key used by the sender, asounder for the receiver, and a battery. THE SENDING KEY. --The base of the sending instrument is six inches long, four inches wide, and three-quarters of an inch thick, made of wood, orany suitable non-conducting material. The key (A) is a piece of brassthree-eighths by one-half inch in thickness and six inches long. Midwaybetween its ends is a cross hole, to receive the pivot pin (B), whichalso passes through a pair of metal brackets (C, D), the bracket Chaving a screw to hold one of the line wires, and the other brackethaving a metal switch (E) hinged thereto. This switch bar, like thebrackets, is made of brass, one-half inch wide by one-sixteenth of aninch thick. Below the forward end of the key (A) is a cross bar of brass (F), screwed to the base by a screw at one end, to receive the other linewire. Directly below the key (A) is a screw (G), so that the key willstrike it when moved downwardly. The other end of the bar (F) contactswith the forward end of the switch bar (E) when the latter is movedinwardly. [Illustration: _Fig. 67. _ TELEGRAPH SENDING KEY] The forward end of the key (A) has a knob (H) for the fingers, and therear end has an elastic (I) attached thereto which is secured to the endof the base, so that, normally, the rear end is held against the baseand away from the screw head (G). The head (J) of a screw projects fromthe base at its rear end. Key A contacts with it. When the key A contacts with the screw heads G, J, a click is produced, one when the key is pressed down and the other when the key is released. You will notice that the two plates C, F are connected up in circuitwith the battery, so that, as the switch E is thrown, so as to be out ofcontact, the circuit is open, and may be closed either by the key A orthe switch E. The use of the switch will be illustrated in connectionwith the sounder. [Illustration: _Fig. 68. _ TELEGRAPH SOUNDER] When the key A is depressed, the circuit of course goes through plate C, key A and plate F to the station signalled. THE SOUNDER. --The sounder is the instrument which carries theelectro-magnet. In Fig. 68 this is shown in perspective. The base is six inches long andfour inches wide, being made, preferably, of wood. Near the forward endis mounted a pair of electro-magnets (A, A), with their terminal wiresconnected up with plates B, B', to which the line wires are attached. Midway between the magnets and the rear end of the base is a pair ofupwardly projecting brackets (C). Between these are pivoted a bar (D), the forward end of which rests between the magnets and carries, thereon, a cross bar (E) which is directly above the magnets, and serves as thearmature. The rear end of the base has a screw (F) directly beneath the bar D ofsuch height that when the rear end of the bar D is in contact therewiththe armature E will be out of contact with the magnet cores (A, A). Aspiral spring (G) secured to the rear ends of the arm and to the base, respectively, serves to keep the rear end of the key normally in contactwith the screw F. CONNECTING UP THE KEY AND SOUNDER. --Having made these two instruments, we must next connect them up in the circuit, or circuits, formed forthem, as there must be a battery, a key, and a sounder at each end ofthe line. In Fig. 69 you will note two groups of those instruments. Now observehow the wires connect them together. There are two line wires, one (A)which connects up the two batteries, the wire being attached so thatone end connects with the positive terminal of the battery, and theother end with the negative terminal. [Illustration: _Fig. 69. _ A TELEGRAPH CIRCUIT] The other line wire (B), between the two stations, has its opposite endsconnected with the terminals of the electro-magnet C of the sounders. The other terminals of each electro-magnet are connected up with oneterminal of each key by a wire (D), and to complete the circuit at eachstation, the other terminal of the key has a wire (E) to its ownbattery. TWO STATIONS IN CIRCUIT. --The illustration shows station 2 telegraphingto station 1. This is indicated by the fact that the switch F' of thatinstrument is open, and the switch F of station 1 closed. When, therefore, the key of station 2 is depressed, a complete circuit isformed which transmits the current through wire E' and battery, throughline A, then through the battery of station 1, through wire E to thekey, and from the key, through wire D, to the sounder, and finally fromthe sounder over line wire B back to the sounder of station 2, completing the circuit at the key through wire D'. When the operator at station 2 closes the switch F', and the operator atstation 1 opens the switch F, the reverse operation takes place. In bothcases, however, the sounder is in at both ends of the line, and only thecircuit through the key is cut out by the switch F, or F'. THE DOUBLE CLICK. --The importance of the double click of the sounderwill be understood when it is realized that the receiving operator musthave some means of determining if the sounder has transmitted a dot or adash. Whether he depresses the key for a dot or a dash, there must beone click when the key is pressed down on the screw head G (Fig. 62), and also another click, of a different kind, when the key is raised upso that its rear end strikes the screw head J. This action of the key isinstantly duplicated by the bar D (Fig. 68) of the sounder, so that thesounder as well as the receiver knows the time between the first and thesecond click, and by that means he learns that a dot or a dash is made. ILLUSTRATING THE DOT AND THE DASH. --To illustrate: Let us suppose, forconvenience, that the downward movement of the lever in the key, and thebar in the sounder, make a sharp click, and the return of the lever andbar make a dull click. In this case the ear, after a little practice, can learn readily how to distinguish the number of downward impulsesthat have been given to the key. _The Morse Telegraph Code_ A . - N - . & . . . . B - . . . O . . 1 . - - . C . . . P . . . . . 2 . . - . . D - . . Q . . - . 3 . . . - . E . R . . . 4 . . . . -F . - . S . . . 5 - - -G - - . T - 6 . . . . . . H . . . . U . . - 7 - - . . I . . V . . . - 8 - . . . . J - . - . W . - - 9 - . . -K - . - X . - . . 0 ---- ------L -- Y . . . . M - - Z . . . . EXAMPLE IN USE. --Let us take an example in the word "electrical. " E L E C T R I C A L. -- . . . . - . . . . . . . . . - -- The operator first makes a dot, which means a sharp and a dull clickclose together; there is then a brief interval, then a lapse, afterwhich there is a sharp click, followed, after a comparatively longerinterval, with the dull click. Now a dash by itself may be an L, a T, orthe figure 0, dependent upon its length. The short dash is T, and thelongest dash the figure 0. The operator will soon learn whether it iseither of these or the letter L, which is intermediate in length. In time the sender as well as receiver will give a uniform length to thedash impulse, so that it may be readily distinguished. In the same way, we find that R, which is indicated by a dot, is followed, after a shortinterval, by two dots. This might readily be mistaken for the single dotfor E and the two dots for I, were it not that the time element in R isnot as long between the first and second dots, as it ordinarily isbetween the single dot of E when followed by the two dots of I. CHAPTER X HIGH TENSION APPARATUS, CONDENSERS, ETC. INDUCTION. --One of the most remarkable things in electricity is theaction of induction--that property of an electric current which enablesit to pass from one conductor to another conductor through the air. Another singular and interesting thing is that the current sotransmitted across spaces changes its direction of flow, and, furthermore, the tension of such a current may be changed bytransmitting it from one conductor to another. LOW AND HIGH TENSION. --In order to effect this latter change--that is, to convert it from a low tension to a high tension--coils are used, onecoil being wound upon the other; one of these coils is called theprimary and the other the secondary. The primary coil receives thecurrent from the battery, or source of electrical power, and thesecondary coil receives charges, and transmits the current. For an illustration of this examine Fig. 70, in which you will note acoil of heavy wire (A), around which is wound a coil of fine wire (B). If, for instance, the primary coil has a low voltage, the secondarycoil will have a high voltage, or tension. Advantage is taken of thisphase to use a few cells, as a primary battery, and then, by a set of_Induction Coils_, as they are called, to build up a high-tensionelectro-motive force, so that the spark will jump across a gap, as shownat C, for the purpose of igniting the charges of gas in a gasolinemotor; or the current may be used for medical batteries, and for otherpurposes. [Illustration: _Fig. 70. _ INDUCTION COIL AND CIRCUIT] The current passes, by induction, from the primary to the secondarycoil. It passes from a large conductor to a small conductor, the smallconductor having a much greater resistance than the large one. ELASTIC PROPERTY OF ELECTRICITY. --While electricity has no resiliency, like a spring, for instance, still it acts in the manner of a cushionunder certain conditions. It may be likened to an oscillating springacted upon by a bar. Referring to Fig. 71, we will assume that the bar A in falling down uponthe spring B compresses the latter, so that at the time of greatestcompression the bar goes down as far as the dotted line C. It is obviousthat the spring B will throw the bar upwardly. Now, electricity appearsto have a kind of elasticity, which characteristic is taken advantage ofin order to increase the efficiency of the induction in the coil. [Illustration: _Fig. 71. _ ILLUSTRATING ELASTICITY] THE CONDENSER. --To make a condenser, prepare two pine boards like A, say, eight by ten inches and a half inch thick, and shellac thoroughlyon all sides. Then prepare sheets of tinfoil (B), six by eight inches insize, and also sheets of paraffined paper (C), seven by nine inches indimensions. Also cut out from the waste pieces of tinfoil strips (D), one inch by two inches. To build up the condenser, lay down a sheet ofparaffined paper (C), then a sheet of tinfoil (B), and before puttingon the next sheet of paraffined paper lay down one of the small strips(D) of tinfoil, as shown in the illustration, so that its end projectsover one end of the board A; then on the second sheet of paraffine paperlay another sheet of tinfoil, and on this, at the opposite end, placeone of the small strips (D), and so on, using from 50 to 100 of thetinfoil sheets. When the last paraffine sheet is laid on, the otherboard is placed on top, and the whole bound together, either by wrappingcords around the same or by clamping them together with bolts. [Illustration: _Fig. 72. _ CONDENSER] You may now make a hole through the projecting ends of the strips, andyou will have two sets of tinfoil sheets, alternately connected togetherat opposite ends of the condenser. Care should be exercised to leave the paraffine sheets perfect orwithout holes. You can make these sheets yourself by soaking them inmelted paraffine wax. CONNECTING UP A CONDENSER. --When completed, one end of the condenser isconnected up with one terminal of the secondary coil, and the other endof the condenser with the other secondary terminal. [Illustration: _Fig. 73. _ HIGH-TENSION CIRCUIT] In Fig. 73 a high-tension circuit is shown. Two coils, side by side, arealways used to show an induction coil, and a condenser is generallyshown, as illustrated, by means of a pair of forks, one resting withinthe other. THE INTERRUPTER. --One other piece of mechanism is necessary, and that isan _Interrupter_, for the purpose of getting the effect of thepulsations given out by the secondary coil. A simple current interrupter is made as follows: Prepare a wooden base(A), one inch thick, six inches wide, and twelve inches long. Upon thismount a toothed wheel (B), six inches in diameter, of thin sheet metal, or a brass gear wheel will answer the purpose. The standard (C), whichsupports the wheel, may be of metal bent up to form two posts, betweenwhich the crankshaft (D) is journaled. The base of the posts has anextension plate (E), with a binding post for a wire. At the front end ofthe base is an L-shaped strip (F), with a binding post for a wireconnection, and the upwardly projecting part of the strip contacts withthe toothed wheel. When the wheel B is rotated the spring finger (F)snaps from one tooth to the next, so that, momentarily, the current isbroken, and the frequency is dependent upon the speed imparted to thewheel. [Illustration: _Fig. 74. _ CURRENT INTERRUPTER] USES OF HIGH-TENSION COILS. --This high-tension coil is made use of, andis the essential apparatus in wireless telegraphy, as we shall see inthe chapter treating upon that subject. CHAPTER XI WIRELESS TELEGRAPHY TELEGRAPHING WITHOUT WIRES. --Wireless telegraphy is an outgrowth of theordinary telegraph system. When Maxwell, and, later on, Hertz, discovered that electricity, magnetism, and light were transmittedthrough the ether, and that they differed only in their wave lengths, they laid the foundations for wireless telegraphy. Ether is a substancewhich is millions and millions of times lighter than air, and itpervades all space. It is so unstable that it is constantly in motion, and this phase led some one to suggest that if a proper electricalapparatus could be made, the ether would thereby be disturbedsufficiently so that its impulses would extend out a distanceproportioned to the intensity of the electrical agitation therebycreated. SURGING CHARACTER OF HIGH-TENSION CURRENTS. --When a current ofelectricity is sent through a wire, hundreds of miles in length, thecurrent surges back and forth on the wire many thousands of times asecond. Light comes to us from the sun, over 90, 000, 000 of miles, through the ether. It is as reasonable to suppose, or infer, that theether can, therefore, convey an electrical impulse as readily as does awire. It is on this principle that impulses are sent for thousands of miles, and no doubt they extend even farther, if the proper mechanism could bedevised to detect movement of the waves so propagated. THE COHERER. --The instrument for detecting these impulses, ordisturbances, in the ether is generally called a _coherer_, althoughdetector is the term which is most satisfactory. The name coherer comesfrom the first practical instrument made for this purpose. [Illustration: _Fig. 75. _ WIRELESS TELEGRAPHY COHERER] HOW MADE. --The coherer is simply a tube, say, of glass, within which isplaced iron filings. When the oscillations surge through the secondarycoil the pressure or potentiality of the current finally causes it toleap across the small space separating the filings and, as it were, itwelds together their edges so that a current freely passes. Thebringing together of the particles, under these conditions, is calledcohering. Fig. 75 shows the simplest form of coherer. The posts (A) are firmlyaffixed to the base (B), each post having an adjusting screw (C) in itsupper end, and these screw downwardly against and serve to bind a pairof horizontal rods (D), the inner ends of which closely approach eachother. These may be adjusted so as to be as near together or as farapart as desired. E is a glass tube in which the ends of the rods (D)rest, and between the separated ends of the rods (D) the iron filings(F) are placed. THE DECOHERERS. --For the purpose of causing the metal filings to fallapart, or decohere, the tube is tapped lightly, and this is done by alittle object like the clapper of an electric bell. In practice, the coils and the parts directly connected with it are puttogether on one base. THE SENDING APPARATUS. --Fig. 76 shows a section of a coil with itsconnection in the sending station. The spark gap rods (A) may be swungso as to bring them closer together or farther apart, but they must notat any time contact with each other. The induction coil has one terminal of the primary coil connected up bya wire (B) with one post of a telegraph key, and the other post of thekey has a wire connection (C), with one side of a storage battery. Theother side of the battery has a wire (D) running to the other terminalof the primary. [Illustration: _Fig. 76. _ WIRELESS SENDING APPARATUS] The secondary coil has one of its terminals connected with a bindingpost (E). This binding post has an adjustable rod with a knob (F) on itsend, and the other binding post (G), which is connected up with theother terminal of the secondary coil, carries a similar adjusting rodwith a knob (H). From the post (E) is a wire (I), which extends upwardly, and is calledthe aerial wire, or wire for the antennę, and this wire also connectswith one side of the condenser by a conductor (J). The ground wire (K)connects with the other binding post (G), and a branch wire (L) alsoconnects the ground wire (K) with one end of the condenser. [Illustration: _Fig. 77. _ WIRELESS RECEIVING APPARATUS] THE RECEIVING APPARATUS. --The receiving station, on the other hand, hasneither condenser, induction coil, nor key. When the apparatus is inoperation, the coherer switch is closed, and the instant a currentpasses through the coherer and operates the telegraph sounder, thegalvanometer indicates the current. Of course, when the coherer switch is closed, the battery operates thedecoherer. HOW THE CIRCUITS ARE FORMED. --By referring again to Fig. 76, it will beseen that when the key is depressed, a circuit is formed from thebattery through wire B to the primary coil, and back again to thebattery through wire D. The secondary coil is thereby energized, and, when the full potential is reached, the current leaps across the gapformed between the two knobs (F, H), thereby setting up a disturbance inthe ether which is transmitted through space in all directions. It is this impulse, or disturbance, which is received by the coherer atthe receiving station, and which is indicated by the telegraph sounder. CHAPTER XII THE TELEPHONE VIBRATIONS. --Every manifestation in nature is by way of vibration. Thebeating of the heart, the action of the legs in walking, the winking ofthe eyelid; the impulses from the sun, which we call light; sound, tasteand color appeal to our senses by vibratory means, and, as we havehereinbefore stated, the manifestations of electricity and magnetism aremerely vibrations of different wave lengths. THE ACOUSTIC TELEPHONE. --That sound is merely a product of vibrationsmay be proven in many ways. One of the earliest forms of telephones wassimply a "sound" telephone, called the _Acoustic Telephone_. Theprinciple of this may be illustrated as follows: Take two cups (A, B), as in Fig. 78, punch a small hole through thebottom of each, and run a string or wire (C) from the hole of one cup tothat of the other, and secure it at both ends so it may be drawn taut. Now, by talking into the cup (A) the bottom of it will vibrate to andfro, as shown by the dotted lines and thereby cause the bottom of theother cup (B) to vibrate in like manner, and in so vibrating it willreceive not only the same amplitude, but also the same character ofvibrations as the cup (A) gave forth. [Illustration: _Fig. 78. _ ACOUSTIC TELEPHONE] [Illustration: _Fig. 79. _ ILLUSTRATING VIBRATIONS] SOUND WAVES. --Sound waves are long and short; the long waves givingsounds which are low in the musical scale, and the short waves highmusical tones. You may easily determine this by the followingexperiment: Stretch a wire, as at B (Fig. 79), fairly tight, and then vibrate it. The amplitude of the vibration will be as indicated by dotted line A. Now, stretch it very tight, as at C, so that the amplitude of vibrationwill be as shown at E. By putting your ear close to the string you willfind that while A has a low pitch, C is very much higher. This is theprinciple on which stringed instruments are built. You will note thatthe wave length, which represents the distance between the dotted linesA is much greater than E. HEARING ELECTRICITY. --In electricity, mechanism has been made to enableman to note the action of the current. By means of the armature, vibrating in front of a magnet, we can see its manifestations. It is nowbut a step to devise some means whereby we may hear it. In this, as ineverything else electrically, the magnet comes into play. [Illustration: _Fig. 80. _ THE MAGNETIC FIELD] In the chapter on magnetism, it was stated that the magnetic fieldextended out beyond the magnet, so that if we were able to see themagnetism, the end of a magnet would appear to us something like amoving field, represented by the dotted lines in Fig. 80. The magnetic field is shown in Fig. 80 at only one end, but itsmanifestations are alike at both ends. It will be seen that the magneticfield extends out to a considerable distance and has quite a radius ofinfluence. THE DIAPHRAGM IN A MAGNETIC FIELD. --If, now, we put a diaphragm (A) inthis magnetic field, close up to the end of the magnet, but not so closeas to touch it, and then push it in and out, or talk into it so that thesound waves strike it, the movement or the vibration of the diaphragm(A) will disturb the magnetic field emanating from the magnet, and thisdisturbance of the magnetic field at one end of the magnet also affectsthe magnetic field at the other end in the same way, so that thedisturbance there will be of the same amplitude. It will also displaythe same characteristics as did the magnetic field when the diaphragm(A) disturbed it. A SIMPLE TELEPHONE CIRCUIT. --From this simple fact grew the telephone. If two magnets are connected up in the same circuit, so that themagnetic fields of the two magnets have the same source of electricpower, the disturbance of one diaphragm will affect the other similarly, just the same as the two magnetic fields of the single magnet aredisturbed in unison. HOW TO MAKE A TELEPHONE. --For experimental and testing purposes two ofthese telephones should be made at the same time. The case or holder(A) may be made either of hard wood or hard rubber, so that it is ofinsulating material. The core (B) is of soft iron, 3/8 inch in diameterand 5 inches long, bored and threaded at one end to receive a screw (C)which passes through the end of the case (A). The enlarged end of the case should be, exteriorly, 2-1/4 inches indiameter, and the body of the case 1 inch in diameter. [Illustration: _Fig. 81. _ SECTION OF TELEPHONE RECEIVER] Interiorly, the large end of the case is provided with a circular recess1-3/4 inches in diameter and adapted to receive therein a spool whichis, diametrically, a little smaller than the recess. The spool fitsfairly tight upon the end of the core, and when in position restsagainst an annular shoulder in the recess. A hollow space (F) is thusprovided behind the spool (D), so the two wires from the magnet mayhave room where they emerge from the spool. The spool is a little shorter than the distance between the shoulder (E)and the end of the casing, at G, and the core projects only a shortdistance beyond the end of the spool, so that when the diaphragm (H) isput upon the end of the case, and held there by screws (I) it will nottouch the end of the core. A wooden or rubber mouthpiece (J) is thenturned up to fit over the end of the case. [Illustration: _Fig. 82. _ THE MAGNET AND RECEIVER HEAD] The spool (D) is made of hard rubber, and is wound with No. 24silk-covered wire, the windings to be well insulated from each other. The two ends of the wire are brought out, and threaded through holes (K)drilled longitudinally through the walls of the case, and affixed to theend by means of screws (L), so that the two wires may be broughttogether and connected with a duplex wire (M). As the screw (C), which holds the core in place, has its head hiddenwithin a recess, which can be closed up by wax, the two terminals of thewires are well separated so that short-circuiting cannot take place. TELEPHONE CONNECTIONS. --The simplest form of telephone connection isshown in Fig. 83. This has merely the two telephones (A and B), with asingle battery (C) to supply electricity for both. One line wire (D)connects the two telephones directly, while the other line (E) has thebattery in its circuit. [Illustration: _Fig. 83. _ SIMPLE TELEPHONE CONNECTION] COMPLETE INSTALLATION. --To install a more complete system requires, ateach end, a switch, a battery and an electro-magneto bell. You may use, for this purpose, a bell, made as shown in the chapter on bells. Fig. 84 shows such a circuit. We now dispense with one of the linewires, because it has been found that the ground between the twostations serves as a conductor, so that only one line wire (A) isnecessary to connect directly with the telephones of the two stations. The telephones (B, B', respectively) have wires (C, C') running to thepivots of double-throw switches (D, D'), one terminal of the switcheshaving wires (E, E'), which go to electric bells (F, F'), and from thebells are other wires (G, G'), which go to the ground. The ground wiresalso have wires (H, H'), which go to the other terminals of the switch(D, D'). The double-throw switch (D, D'), in the two stations, is thrownover so the current, if any should pass through, will go through thebell to the ground, through the wires (E, G or E', G'). [Illustration: _Fig. 84. _ TELEPHONE STATIONS IN CIRCUIT] Now, supposing the switch (D'), in station 2, should be thrown over soit contacts with the wire (H'). It is obvious that the current will thenflow from the battery (I') through wires (H', C') and line (A) tostation 1; then through wire C, switch D, wire E to the bell F, to theground through wire G. From wire G the current returns through theground to station 2, where it flows up wire G' to the battery, therebycompleting the circuit. [Illustration: _Fig. 85. _ ILLUSTRATING LIGHT CONTACT POINTS] The operator at station 2, having given the signal, again throws hisswitch (D') back to the position shown in Fig. 84, and the operator atstation 1 throws on his switch (D), so as to ring the bell in station 2, thereby answering the signal, which means that both switches are againto be thrown over so they contact with the battery wires (H and H'), respectively. When both are thus thrown over, the bells (G, G') are cutout of the circuit, and the batteries are both thrown in, so that thetelephones are now ready for talking purposes. MICROPHONE. --Originally this form of telephone system was generallyemployed, but it was found that for long distances a more sensitiveinstrument was necessary. LIGHT CONTACT POINTS. --In 1877 Professor Hughes discovered, accidentally, that a light contact point in an electric circuitaugmented the sound in a telephone circuit. If, for instance, a lightpin, or a nail (A, Fig. 85) should be used to connect the severed endsof a wire (B), the sounds in the telephone not only would be louder, butthey would be more distinct, and the first instrument made practically, to demonstrate this, is shown in Fig. 86. [Illustration: _Fig. 86. _ MICROPHONE] [Illustration: _Fig. 87. _ TRANSMITTER] HOW TO MAKE A MICROPHONE. --This instrument has simply a base (A) ofwood, and near one end is a perpendicular sounding-board (B) of wood, toone side of which is attached, by wax or otherwise, a pair of carbonblocks (C, D). The lower carbon block (C) has a cup-shaped depression inits upper side, and the upper block has a similar depression in itslower side. A carbon pencil (E) is lightly held within these cups, sothat the lightest contact of the upper end of the pencil with thecarbon block, makes the instrument so sensitive that a fly, walking uponthe sounding-board, may be distinctly heard through the telephone whichis in the circuit. MICROPHONE THE FATHER OF THE TRANSMITTER. --This instrument has beengreatly modified, and is now used as a transmitter, the latter therebytaking the place of the pin (A), shown in Fig. 85. AUTOMATIC CUT-OUTS FOR TELEPHONES. --In the operation of the telephone, the great drawback originally was in inducing users of the lines toreplace or adjust their instruments carefully. When switches were used, they would forget to throw them back, and all sorts of trouble resulted. It was found necessary to provide an automatic means for throwing in andcutting out an instrument, this being done by hanging the telephone onthe hook, so that the act merely of leaving the telephone made itnecessary, in replacing the instrument, to cut out the apparatus. Before describing the circuiting required for these improvements, weshow, in Fig. 87, a section of a transmitter. A cup-shaped case (A) is provided, made of some insulating material, which has a diaphragm (B) secured at its open side. This diaphragmcarries the carbon pencil (C) on one side and from the blocks whichsupport the carbon pencil the wires run to binding posts on the case. Of course the carbon supporting posts must be insulated from each other, so the current will go through the carbon pencil (C). COMPLETE CIRCUITING WITH TRANSMITTER. --In showing the circuiting (Fig. 88) it will not be possible to illustrate the boxes, or casings, whichreceive the various instruments. For instance, the hook which carriesthe telephone or the receiver, is hinged within the transmitter box. Thecircuiting is all that it is intended to show. [Illustration: _Fig. 88. _ COMPLETE TELEPHONIC CIRCUIT] The batteries of the two stations are connected up by a wire (A), unlessa ground circuit is used. The other side of each battery has a wireconnection (B, B') with one terminal of the transmitter, and the otherterminal of the transmitter has a wire (C, C') which goes to thereceiver. From the other terminal of the receiver is a wire (D, D')which leads to the upper stop contact (E, E') of the telephone hook. Awire (F, F') from the lower stop contact (G, G') of the hook goes to oneterminal of the bell, and from the other terminal of the bell is a wire(H, H') which makes connection with the line wire (A). In order to makea complete circuit between the two stations, a line wire (I) is run fromthe pivot of the hook in station 1 to the pivot of the hook in station2. In the diagram, it is assumed that the receivers are on the hooks, andthat both hooks are, therefore, in circuit with the lower contacts (G, G'), so that the transmitter and receiver are both out of circuit withthe batteries, and the bell in circuit; but the moment the receiver, forinstance, in station 1 is taken off the hook, the latter springs up sothat it contacts with the stop (E), thus establishing a circuit throughthe line wire (I) to the hook of station 2, and from the hook throughline (F') to the bell. From the bell, the line (A) carries the currentback to the battery of station (A), thence through the wire (B) to thetransmitter wire (C) to receiver and wire (D) to the post (E), therebycompleting the circuit. When, at station 2, the receiver is taken off the hook, and the lattercontacts with the post (E'), the transmitter and receiver of bothstations are in circuit with each other, but both bells are cut out. CHAPTER XIII ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING DECOMPOSING LIQUIDS. --During the earlier experiments in the field ofelectricity, after the battery or cell was discovered, it was noted thatwhen a current was formed in the cell, the electrolyte was charged andgases evolved from it. A similar action takes place when a current ofelectricity passes through a liquid, with the result that the liquid isdecomposed--that is, the liquid is broken up into its originalcompounds. Thus, water is composed of two parts, by bulk, of hydrogenand of oxygen, so that if two electrodes are placed in water, and acurrent is sent through the electrodes in either direction, all thewater will finally disappear in the form of hydrogen and oxygen gases. MAKING HYDROGEN AND OXYGEN. --During this electrical action, the hydrogenis set free at the negative pole and the oxygen at the positive pole. Asimple apparatus, which any boy can make, to generate pure oxygen andpure hydrogen, is shown in Fig. 89. It is constructed of a glass or earthen jar (A), preferably square, towhich is fitted a wooden top (B), this top being provided with apacking ring (C), so as to make it air-tight. Within is a verticalpartition (D), the edges of which, below the cap, fit tightly againstthe inner walls of the jar. This partition extends down into the jar asufficient distance so it will terminate below the water level. A pipeis fitted through the top on each side of the partition, and each pipehas a valve. An electrode, of any convenient metal, is secured at itsupper end to the top of the cap, on each side of the partition. Theseelectrodes extend down to the bottom of the jar, and an electric wireconnects with each of them at the top. [Illustration: _Fig. 89. _ DEVICE FOR MAKING HYDROGEN AND OXYGEN] If a current of electricity is passed through the wires and theelectrodes, in the direction shown by the darts, hydrogen will form atthe negative pole, and oxygen at the positive pole. These gases willescape upwardly, so that they will be trapped in their respectivecompartments, and may be drawn off by means of the pipes. PURIFYING WATER. --Advantage is taken of this electrolytic action, topurify water. Oxygen is the most wonderful chemical in nature. It iscalled the acid-maker of the universe. The name is derived from twowords, _oxy_ and _gen_; one denoting oxydation, and the other that itgenerates. In other words, it is the _generator of oxides_. It is theelement which, when united with any other element, produces an acid, analkali or a neutral compound. RUST. --For instance, iron is largely composed of ferric acid. Whenoxygen, in a free or gaseous state, comes into contact with iron, itproduces ferrous oxide, which is recognized as rust. OXYGEN AS A PURIFIER. --But oxygen is also a purifier. All low forms ofanimal life, like bacteria or germs in water, succumb to free oxygen. By_free oxygen_ is meant oxygen in the form of gas. COMPOSITION OF WATER. --Now, water, in which harmful germs live, isone-third oxygen. Nevertheless, the germs thrive in water, because theoxygen is in a compound state, and, therefore, not an active agent. Butif oxygen, in the form of gas, can be forced through water, it willattack the germs, and destroy them. COMMON AIR NOT A GOOD PURIFIER. --Water may be purified, to a certainextent, by forcing common air through it, and the foulest water, if runover rocks, will be purified, in a measure, because air is intermingledwith it. But common air is composed of four-fifths nitrogen, and onlyone-fifth oxygen, and, as nitrogen is the staple article of food forbacteria, the purifying method by air is not effectual. PURE OXYGEN. --When, however, oxygen is generated from water, by means ofelectrolysis, it is pure; hence is more active and is not tainted by alife-giving substance for germs, such as nitrogen. The mechanism usually employed for purifying water is shown in Fig. 90. A WATER PURIFIER. --The case (A, Fig. 90) may be made of metal or of aninsulating material. If made of metal it must be insulated within withslate, glass, marble or hard rubber, as shown at B. The case is providedwith exterior flanges (C, D), with upper and lower ends, and it ismounted upon a base plate (E) and affixed thereto by bolts. The upperend has a conically-formed cap (F) bolted to the flanges (C), and thishas an outlet to which a pipe (G) is attached. The water inlet pipe (H)passes through the lower end of the case (A). The electrodes (I, J) aresecured, vertically, within the case, separated from each otherequidistant, each alternate electrode being connected up with one wire(K), and the alternate electrodes with a wire (L). [Illustration: _Fig. 90. _ ELECTRIC WATER PURIFIER] When the water passes upwardly, the decomposed or gaseous oxygenpercolates through the water and thus attacks the germs and destroysthem. THE USE OF HYDROGEN IN PURIFICATION. --On the other hand, the hydrogenalso plays an important part in purifying the water. This depends uponthe material of which the electrodes are made. Aluminum is by far thebest material, as it is one of nature's most active purifiers. All claycontains aluminum, in what is known as the sulphate form, and waterpassing through the clay of the earth thereby becomes purified, becauseof this element. ALUMINUM ELECTRODES. --When this material is used as the electrodes inwater, hydrate of aluminum is formed, or a compound of hydrogen andoxygen with aluminum. The product of decomposition is a flocculentmatter which moves upwardly through the water, giving it a milkyappearance. This substance is like gelatine, so that it entangles orenmeshes the germ life and prevents it from passing through a filter. If no filter is used, this flocculent matter, as soon as it has givenoff the gases, will settle to the bottom and carry with it alldecomposed matter, such as germs and other organic matter attacked bythe oxygen, which has become entangled in the aluminum hydrate. ELECTRIC HAND PURIFIER. --An interesting and serviceable little purifiermay be made by any boy with the simplest tools, by cutting out threepieces of sheet aluminum. Hard rolled is best for the purpose. It isbetter to have one of the sheets (A), the middle one, thicker than thetwo outer plates (B). [Illustration: _Fig. 91. _ PORTABLE ELECTRIC PURIFIER] Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-halfinch from the upper ends of the two outside plates (B, B) bore boltholes (C), each of these holes being a quarter of an inch from the edgeof the plate. The inside plate (A) has two large holes (D) correspondingwith the small holes (C) in the outside plates. At the upper end of thisplate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with asmall hole for a bolt. Next cut out two hard-rubber blocks (F), each1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole(G) through each, corresponding with the small holes (C) in the plates(B). The machine is now ready to be assembled. If the inner plate is 1/8inch thick and the outer plates each 1/16 inch thick, use two smalleighth-inch bolts 1-1/4 inches long, and clamp together the threeplates with these bolts. One of the bolts may be used to attach theretoone of the electric wires (H), and the other wire (I) is attached by abolt to the wing (E). [Illustration: _Figs. 92-95. _ DETAILS OF PORTABLE PURIFIER] Such a device will answer for a 110-volt circuit, in ordinary water. Nowfill a glass nearly full of water, and stand the purifier in the glass. Within a few minutes the action of electrolysis will be apparent by theformation of numerous bubbles on the plates, followed by thedecomposition of the organic matter in the water. At first theflocculent decomposed matter will rise to the surface of the water, butbefore many minutes it will settle to the bottom of the glass and leaveclear water above. PURIFICATION AND SEPARATION OF METALS. --This electrolytic action isutilized in metallurgy for the purpose of producing pure metals, but itis more largely used to separate copper from its base. In order toutilize a current for this purpose, a high ampere flow and low voltageare required. The sheets of copper, containing all of its impurities, are placed within a tank, parallel with a thin copper sheet. The impuresheet is connected with the positive pole of an electroplating dynamo, and the thin sheet of copper is connected with the negative pole. Theelectrolyte in the tank is a solution of sulphate of copper. The actionof the current will cause the pure copper in the impure sheet todisintegrate and it is then carried over and deposited upon the thinsheet, this action continuing until the impure sheet is entirely eatenaway. All the impurities which were in the sheet fall to the bottom ofthe tank. Other metals are treated in the same way, and this treatment has a verywide range of usefulness. ELECTROPLATING. --The next feature to be considered in electrolysis is amost interesting and useful one, because a cheap or inferior metal maybe coated by a more expensive metal. Silver and nickel plating arebrought about by this action of a current passing through metals, whichare immersed in an electrolyte. PLATING IRON WITH COPPER. --We have room in this chapter for only oneconcrete example of this work, which, with suitable modifications, is anexample of the art as practiced commercially. Iron, to a considerableextent, is now being coated with copper to preserve it from rust. Tocarry out this work, however, an electroplating dynamo, of largeamperage, is required, the amperage, of course, depending upon thesurface to be treated at one time. The pressure should not exceed 5volts. The iron surface to be treated should first be thoroughly cleansed, andthen immediately put into a tank containing a cyanide of coppersolution. Two forms of copper solution are used, namely, the cyanide, which is a salt solution of copper, and the sulphate, which is an acidsolution of copper. Cyanide is first used because it does not attack theiron, as would be the case if the sulphate solution should first comeinto contact with the iron. A sheet of copper, termed the anode, is then placed within the tank, parallel with the surface to be plated, known as the cathode, and somounted that it may be adjusted to or from the iron surface, or cathode. A direct current of electricity is then caused to flow through thecopper plate and into the iron plate or surface, and the platingproceeded with until the iron surface has a thin film of copperdeposited thereon. This is a slow process with the cyanide solution, soit is discontinued as soon as possible, after the iron surface has beencompletely covered with copper. This copper surface is thoroughlycleaned off to remove therefrom the saline or alkaline solution, and itis then immersed within a bath, containing a solution of sulphate ofcopper. The current is then thrown on and allowed so to remain until ithas deposited the proper thickness of copper. DIRECTION OF CURRENT. --If a copper and an iron plate are put into acopper solution and connected up in circuit with each other, a primarybattery is thereby formed, which will generate electricity. In thiscase, the iron will be positive and the copper negative, so that thecurrent within such a cell would flow from the iron (in this instance, the anode) to the negative, or cathode. The action of electroplating reverses this process and causes thecurrent to flow from the copper to the iron (in this instance, thecathode). CHAPTER XIV ELECTRIC HEATING, THERMO ELECTRICITY GENERATING HEAT IN A WIRE. --When a current of electricity passes througha conductor, like a wire, more or less heat is developed in theconductor. This heat may be so small that it cannot be measured, but itis, nevertheless, present in a greater or less degree. Conductors offera resistance to the passage of a current, just the same as water finds aresistance in pipes through which it passes. This resistance is measuredin ohms, as explained in a preceding chapter, and it is this resistancewhich is utilized for electric heating. RESISTANCE OF SUBSTANCES. --Silver offers less resistance to the passageof a current than any other metal, the next in order is copper, whileiron is, comparatively, a poor conductor. The following is a partial list of metals, showing their relativeconductivity: Silver 1. Copper 1. 04 to 1. 09Gold 1. 38 to 1. 41Aluminum 1. 64Zinc 3. 79Nickel 4. 69Iron 6. 56Tin 8. 9Lead 13. 2German Silver 12. 2 to 15 From this table it will be seen that, for instance, iron offers six anda half times the resistance of silver, and that German silver hasfifteen times the resistance of silver. This table is made up of strands of the different metals of the samediameters and lengths, so as to obtain their relative values. SIZES OF CONDUCTORS. --Another thing, however, must be understood. If twoconductors of the same metal, having different diameters, receive thesame current of electricity, the small conductor will offer a greaterresistance than the large conductor, hence will generate more heat. Thiscan be offset by increasing the diameter of the conductor. The metalused is, therefore, of importance, on account of the cost involved. COMPARISON OF METALS. --A conductor of aluminum, say, 10 feet long and ofthe same weight as copper, has a diameter two and a quarter timesgreater than copper; but as the resistance of aluminum is 50 per cent. More than that of silver, it will be seen that, weight for weight, copper is the cheaper, particularly as aluminum costs fully three timesas much as copper. [Illustration: _Fig. 96. _ SIMPLE ELECTRIC HEATER] The table shows that German silver has the highest resistance. Ofcourse, there are other metals, like antimony, platinum and the like, which have still higher resistance. German silver, however, is mostcommonly used, although there are various alloys of metal made whichhave high resistance and are cheaper. The principle of all electric heaters is the same, namely, theresistance of a conductor to the passage of a current, and anillustration of a water heater will show the elementary principles inall of these devices. A SIMPLE ELECTRIC HEATER. --In Fig. 96 the illustration shows a cup orholder (A) for the wire, made of hard rubber. This may be of suchdiameter as to fit upon and form the cover for a glass (B). The rubbershould be 1/2 inch thick. Two holes are bored through the rubber cup, and through them are screwed two round-headed screws (C, D), each screwbeing 1-1/2 inches long, so they will project an inch below the cap. Each screw should have a small hole in its lower end to receive a pin(E) which will prevent the resistance wire from slipping off. The resistance wire (F) is coiled for a suitable length, dependent uponthe current used, one end being fastened by wrapping it around the screw(C). The other end of the wire is then brought upwardly through theinterior of the coil and secured in like manner to the other screw (D). Caution must be used to prevent the different coils or turns fromtouching each other. When completed, the coil may be immersed in water, the current turned on, and left so until the water is sufficientlyheated. [Illustration: _Figs. 97-98. _ RESISTANCE DEVICE] HOW TO ARRANGE FOR QUANTITY OF CURRENT USED. --It is difficult todetermine just the proper length the coil should be, or the sizes of thewire, unless you know what kind of current you have. You may, however, rig up your own apparatus for the purpose of making it fit your heater, by preparing a base of wood (A) 8 inches long, 3 inches wide and 1 inchthick. On this mount four electric lamp sockets (B). Then connect theinlet wire (C) by means of short pieces of wire (D) with all the socketson one side. The outlet wire (E) should then be connected up with theother sides of the sockets by the short wires (F). If, now, we have one16-candlepower lamp in one of the sockets, there is a half ampere goingthrough the wires (C, F). If there are two lamps on the board you willhave 1 ampere, and so on. By this means you may readily determine howmuch current you are using and it will also afford you a means offinding out whether you have too much or too little wire in your coil todo the work. [Illustration: _Fig. 99. _ PLAN VIEW OF ELECTRIC IRON] AN ELECTRIC IRON. --An electric iron is made in the same way. The upperside of a flatiron has a circular or oval depression (A) cast therein, and a spool of slate (B) is made so it will fit into the depression andthe high resistance wire (C) is wound around this spool, and insulatingmaterial, such as asbestos, must be used to pack around it. Centrally, the slate spool has an upwardly projecting circular extension (D) whichpasses through the cap or cover (E) of the iron. The wires of theresistance coil are then brought through this circular extension andare connected up with the source of electrical supply. Wires are nowsold for this purpose, which are adapted to withstand an intense heat. [Illustration: _Fig. 100. _ SECTION OF ELECTRIC IRON] The foregoing example of the use of the current, through resistancewires, has a very wide application, and any boy, with these examplesbefore him, can readily make these devices. THERMO ELECTRICITY. --It has long been the dream of scientists to convertheat directly into electricity. The present practice is to use a boilerto generate steam, an engine to provide the motion, and a dynamo toconvert that motion into electricity. The result is that there is lossin the process of converting the fuel heat into steam; loss to changethe steam into motion, and loss to make electricity out of the motionof the engine. By using water-power there is less actual loss; butwater-power is not available everywhere. CONVERTING HEAT DIRECTLY INTO ELECTRICITY. --Heat may be converteddirectly into electricity without using a boiler, an engine or a dynamo, but it has not been successful from a commercial standpoint. It isinteresting, however, to know and understand the subject, and for thatreason it is explained herein. METALS; ELECTRIC POSITIVE-NEGATIVE. --To understand the principle, it maybe stated that all metals are electrically positive-negative to eachother. You will remember that it has hereinbefore been stated that if, for instance, iron and copper are put into an acid solution, a currentwill be created or generated thereby. So with zinc and copper, the usualprimary battery elements. In all such cases an electrolyte is used. Thermo-electricity dispenses with the electrolyte, and nothing is usedbut the metallic elements and heat. The word thermo means heat. If, now, we can select two strips of different metals, and place them as farapart as possible--that is, in their positive-negative relations witheach other, and unite the end of one with one end of other by means of arivet, and then heat the riveted ends, a current will be generated inthe strips. If, for instance, we use an iron in conjunction with acopper strip, the current will flow from the copper to the iron, becausecopper is positive to iron, and iron negative to copper. It is from thisthat the term positive-negative is taken. The two metals most available, which are thus farthest apart in thescale of positive-negative relation, are bismuth and antimony. [Illustration: _Fig. 101. _ THERMO-ELECTRIC COUPLE] In Fig. 101 is shown a thermo-electric couple (A, B) riveted together, with thin outer ends connected by means of a wire (C) to form a circuit. A galvanometer (D) or other current-testing means is placed in thiscircuit. A lamp is placed below the joined ends. THERMO-ELECTRIC COUPLES. --Any number of these couples may be puttogether and joined at each end to a common wire and a fairly large flowof current obtained thereby. One thing must be observed: A current will be generated only so long asthere exists a difference in temperature between the inner and the outerends of the bars (A, B). This may be accomplished by water, or any othercooling means which may suggest itself. CHAPTER XV ALTERNATING CURRENTS, CHOKING COILS, TRANSFORMERS, CONVERTERS ANDRECTIFIERS DIRECT CURRENT. --When a current of electricity is generated by a cell, it is assumed to move along the wire in one direction, in a steady, continuous flow, and is called a _direct_ current. This direct currentis a natural one if generated by a cell. ALTERNATING CURRENT. --On the other hand, the natural current generatedby a dynamo is alternating in its character--that is, it is not adirect, steady flow in one direction, but, instead, it flows for aninstant in one direction, then in the other direction, and so on. A direct-current dynamo such as we have shown in Chapter IV, is mucheasier to explain, hence it is illustrated to show the third method usedin generating an electric current. It is a difficult matter to explain the principle and operation ofalternating current machines, without becoming, in a measure, tootechnical for the purposes of this book, but it is important to know thefundamentals involved, so that the operation and uses of certainapparatus, like the choking coil, transformers, rectifiers andconverters, may be explained. THE MAGNETIC FIELD. --It has been stated that when a wire passes throughthe magnetic field of a magnet, so as to cut the lines of force flowingout from the end of a magnet, the wire will receive a charge ofelectricity. [Illustration: _Fig. 102. _ CUTTING A MAGNETIC FIELD] To explain this, study Fig. 102, in which is a bar magnet (A). If wetake a metal wire (B) and bend it in the form of a loop, as shown, andmount the ends on journal-bearing blocks, the wire may be rotated sothat the loop will pass through the magnetic field. When this takesplace, the wire receives a charge of electricity, which moves, say, inthe direction of the darts, and will make a complete circuit if the endsof the looped wire are joined, as shown by the conductor (D). ACTION OF THE MAGNETIZED WIRE. --You will remember, also that we havepointed out how, when a current passes over a wire, it has a magneticfield extending out around it at all points, so that while it is passingthrough the magnetic field of the magnet (A), it becomes, in a measure, a magnet of its own and tries to set up in business for itself as agenerator of electricity. But when the loop leaves the magnetic field, the magnetic or electrical impulse in the wire also leaves it. THE MOVEMENT OF A CURRENT IN A CHARGED WIRE. --Your attention isdirected, also, to another statement, heretofore made, namely, that whena current from a charged wire passes by induction to a wire acrossspace, so as to charge it with an electric current, it moves along thecharged wire in a direction opposite to that of the current in thecharging wire. Now, the darts show the direction in which the current moves while it isapproaching and passing through the magnetic field. But the moment theloop is about to pass out of the magnetic field, the current in the loopsurges back in the opposite direction, and when the loop has made arevolution and is again entering the magnetic field, it must againchange the direction of flow in the current, and thus producealternations in the flow thereof. Let us illustrate this by showing the four positions of the revolvingloop. In Fig. 103 the loop (B) is in the middle of the magnetic field, moving upwardly in the direction of the curved dart (A), and while inthat position the voltage, or the electrical impulse, is the mostintense. The current used flows in the direction of the darts (C) or tothe left. In Fig. 104, the loop (A) has gone beyond the influence of the magneticfield, and now the current in the loop tries to return, or reverseitself, as shown by the dart (D). It is a reaction that causes thecurrent to die out, so that when the loop has reached the point farthestfrom the magnet, as shown in Fig. 105, there is no current in the loop, or, if there is any, it moves faintly in the direction of the dart (E). [Illustration: _Figs. 103-106. _ ILLUSTRATING ALTERNATIONS] CURRENT REVERSING ITSELF. --When the loop reaches its lowest point (Fig. 106) it again comes within the magnetic field and the current commencesto flow back to its original direction, as shown by darts (C). SELF-INDUCTION. --This tendency of a current to reverse itself, under theconditions cited, is called self-induction, or inductance, and it wouldbe well to keep this in mind in pursuing the study of alternatingcurrents. You will see from the foregoing, that the alternations, or the change ofdirection of the current, depends upon the speed of rotation of the looppast the end of the magnet. [Illustration: _Figs. 107-108. _ FORM FOR INCREASING ALTERNATIONS] Instead, therefore, of using a single loop, we may make four loops (Fig. 107), which at the same speed as we had in the case of the single loop, will give four alternations, instead of one, and still further, toincrease the periods of alternation, we may use the four loops and twomagnets, as in Fig. 108. By having a sufficient number of loops and ofmagnets, there may be 40, 50, 60, 80, 100 or 120 such alternatingperiods in each second. Time, therefore, is an element in the operationof alternating currents. Let us now illustrate the manner of connecting up and building thedynamo, so as to derive the current from it. In Fig. 109, the loop (A)shows, for convenience, a pair of bearings (B). A contact finger (C)rests on each, and to these the circuit wire (D) is attached. Do notconfuse these contact fingers with the commutator brushes, shown in thedirect-current motor, as they are there merely for the purpose of makingcontact between the revolving loop (A) and stationary wire (D). [Illustration: _Fig. 109. _ CONNECTION OF ALTERNATING DYNAMO ARMATURE] BRUSHES IN A DIRECT-CURRENT DYNAMO. --The object of the brushes in thedirect-current dynamo, in connection with a commutator, is to convertthis _inductance_ of the wire, or this effort to reverse itself into acurrent which will go in one direction all the time, and not in bothdirections alternately. To explain this more fully attention is directed to Figs. 110 and 111. Let A represent the armature, with a pair of grooves (B) for the wires. The commutator is made of a split tube, the parts so divided beinginsulated from each other, and in Fig. 110, the upper one, we shall calland designate the positive (+) and the lower one the negative (-). Thearmature wire (C) has one end attached to the positive commutatorterminal and the other end of this wire is attached to the negativeterminal. [Illustration: _Fig. 110. _ DIRECT CURRENT DYNAMO] One brush (D) contacts with the positive terminal of the commutator andthe other brush (E) with the negative terminal. Let us assume that thecurrent impulse imparted to the wire (C) is in the direction of the dart(F, Fig. 110). The current will then flow through the positive (+)terminal of the commutator to the brush (D), and from the brush (D)through the wire (G) to the brush (E), which contacts with the negative(-) terminal of the commutator. This will continue to be the case, whilethe wire (C) is passing the magnetic field, and while the brush (D) isin contact with the positive (+) terminal. But when the armature makes ahalf turn, or when it reaches that point where the brush (D) contactswith the negative (-) terminal, and the brush (E) contacts with thepositive (+) terminal, a change in the direction of the current throughthe wire (G) takes place, unless something has happened to change itbefore it has reached the brushes (D, E). [Illustration: _Fig. 111. _ CIRCUIT WIRES IN DIRECT CURRENT DYNAMO] Now, this change is just exactly what has happened in the wire (C), aswe have explained. The current attempts to reverse itself and start outon business of its own, so to speak, with the result that when thebrushes (D and E) contact with the negative and positive terminals, respectively, the surging current in the wire (C) is going in thedirection of the dart (H)--that is, while, in Fig. 110, the currentflows from the wire (C) into the positive terminal, and out of thenegative terminal into the wire (C), the conditions are exactly reversedin Fig. 111. Here the current in wire C flows _into_ the negative (-)terminal, and _from_ the positive (+) terminal into the wire C, so thatin either case the current will flow out of the brush D and into thebrush E, through the external circuit (G). It will be seen, therefore, that in the direct-current motor, advantageis taken of the surging, or back-and-forth movement, of the current topass it along in one direction, whereas in the alternating current nosuch change in direction is attempted. ALTERNATING POSITIVE AND NEGATIVE POLES. --The alternating current, owing to this surging movement, makes the poles alternately positive andnegative. To express this more clearly, supposing we take a line (A, Fig. 112), which is called the zero line, or line of no electricity. Thecurrent may be represented by the zigzag line (B). The lines (B) abovezero (A) may be designated as positive, and those below the line asnegative. The polarity reverses at the line A, goes up to D, which isthe maximum intensity or voltage above zero, and, when the current fallsand crosses the line A, it goes in the opposite direction to E, which isits maximum voltage in the other direction. In point of time, if ittakes one second for the current to go from C to F, on the down line, then it takes only a half second to go from C to G, so that the line Arepresents the time, and the line H the intensity, a complete cyclebeing formed from C, D, F, then through F, E, C, and so on. [Illustration: _Fig. 112. _ ALTERNATING POLARITY LINES] HOW AN ALTERNATING DYNAMO IS MADE. --It is now necessary to apply theseprinciples in the construction of an alternating-current machine. Fig. 113 is a diagram representing the various elements, and the circuiting. [Illustration: _Fig. 113. _ ALTERNATING CURRENT DYNAMO] Let A represent the ring or frame containing the inwardly projectingfield magnet cores (B). C is the shaft on which the armature revolves, and this carries the wheel (D), which has as many radially disposedmagnet cores (E) as there are of the field magnet cores (B). The shaft (C) also carries two pulleys with rings thereon. One of theserings (F) is for one end of the armature winding, and the other ring(G) for the other end of the armature wire. THE WINDINGS. --The winding is as follows: One wire, as at H, is firstcoiled around one magnet core, the turnings being to the right. Theoutlet terminal of this wire is then carried to the next magnet core andwound around that, in the opposite direction, and so on, so that theterminal of the wire is brought out, as at I, all of these wires beingconnected to binding posts (J, J'), to which, also, the working circuitsare attached. THE ARMATURE WIRES. --The armature wires, in like manner, run from thering (G) to one armature core, being wound from right to left, then tothe next core, which is wound to the right, afterward to the next core, which is wound to the left, and so on, the final end of the wire beingconnected up with the other ring (F). The north (N) and the south (S)poles are indicated in the diagram. CHOKING COIL. --The self-induction in a current of this kind is utilizedin transmitting electricity to great distances. Wires offer resistance, or they impede the flow of a current, as hereinbefore stated, so that itis not economical to transmit a direct current over long distances. Thiscan be done more efficiently by means of the alternating current, whichis subject to far less loss than is the case with the direct current. It affords a means whereby the flow of a current may be checked orreduced without depending upon the resistance offered by the wire overwhich it is transmitted. This is done by means of what is called achoking coil. It is merely a coil of wire, wound upon an iron core, andthe current to be choked passes through the coil. To illustrate this, let us take an arc lamp designed to use a 50-volt current. If a currentis supplied to it carrying 100 volts, it is obvious that there are 50volts more than are needed. We must take care of this excess of 50 voltswithout losing it, as would happen were we to locate a resistance ofsome kind in the circuit. This result we accomplish by the introductionof the choking coil, which has the effect of absorbing the excessive 50volts, the action being due to its quality of self-induction, referredto in the foregoing. [Illustration: _Fig. 114. _ CHOKING COIL] In Fig. 114, A is the choking coil and B an arc lamp, connected up, inseries, with the choking coil. THE TRANSFORMER. --It is more economical to transmit 10, 000 volts a longdistance than 1, 000 volts, because the lower the pressure, or thevoltage, the larger must be the conductor to avoid loss. It is for thisreason that 500 volts, or more, are used on electric railways. Forelectric light purposes, where the current goes into dwellings, eventhis is too high, so a transformer is used to take a high-voltagecurrent from the main line and transform it into a low voltage. This isdone by means of two distinct coils of wire, wound upon an iron core. [Illustration: _Fig. 115. _ A TRANSFORMER] In Fig. 115 the core is O-shaped, so that a primary winding (A), fromthe electrical source, can be wound upon one limb, and the secondarywinding (B) wound around the other limb. The wires, to supply thelamps, run from the secondary coil. There is no electrical connectionbetween the two coils, but the action from the primary to the secondarycoil is solely by induction. When a current passes through the primarycoil, the surging movement, heretofore explained, is transmitted to theiron core, and the iron core, in turn, transmits this electrical energyto the secondary coil. HOW THE VOLTAGE IS DETERMINED. --The voltage produced by the secondarycoil will depend upon several things, namely, the strength of themagnetism transmitted to it; the rapidity, or periodicity of thecurrent, and the number of turns of wire around the coil. The voltage isdependent upon the length of the winding. But the voltage may also beincreased, as well as decreased. If the primary has, we will say, 100turns of wire, and has 200 volts, and the secondary has 50 turns ofwire, the secondary will give forth only one-half as much as theprimary, or 100 volts. If, on the other hand, 400 volts would be required, the secondary shouldhave 200 turns in the winding. VOLTAGE AND AMPERAGE IN TRANSFORMERS. --It must not be understood that, by increasing the voltage in this way, we are getting that much moreelectricity. If the primary coil, with 100 turns, produces a current of200 volts and 50 amperes, which would be 200 × 50 = 10, 000 watts, andthe secondary coil has 50 turns, we shall have 100 volts and 100amperes: 100 (V. ) × 100 (A. ) = 10, 000 watts. Or, if, on the other hand, our secondary winding is composed of 200 turns, we shall have 400 voltsand 25 amperes, 400 (volts) × 25 (amperes) also gives 10, 000 watts. Necessarily, there will be some loss, but the foregoing is offered asthe theoretical basis of calculation. CHAPTER XVI ELECTRIC LIGHTING The most important step in the electric field, after the dynamo had beenbrought to a fairly workable condition, was its utilization to makelight. It was long known prior to the discovery of practical electricdynamos, that the electric current would produce an intense heat. Ordinary fuels under certain favorable conditions will produce atemperature of 4, 500 degrees of heat; but by means of the electric arc, as high as six, eight and ten thousand degrees are available. The fact that when a conductor, in an electric current, is severed, aspark will follow the drawing part of the broken ends, led manyscientists to believe, even before the dynamo was in a practical shape, that electricity, sooner or later, would be employed as the greatlighting agent. When the dynamo finally reached a stage in development where itsoperation could be depended on, and was made reversible, the firstactive steps were taken to not only produce, but to maintain an arcbetween two electrodes. It would be difficult and tedious to follow out the first experimentsin detail, and it might, also, be useless, as information, in view ofthe present knowledge of the science. A few steps in the course of thedevelopment are, however, necessary to a complete understanding of thesubject. Reference has been made in a previous chapter to what is called the_Electric Arc_, produced by slightly separated conductors, across whichthe electric current jumps, producing the brilliantly lighted area. This light is produced by the combustion of the carbon of which theelectrodes are composed. Thus, the illumination is the result ofdirectly burning a fuel. The current, in passing from one electrode tothe other, through the gap, produces such an intense heat that the fuelthrough which the current passes is consumed. Carbon in a comparatively pure state is difficult to ignite, owing toits great resistance to heat. At about 7, 000 degrees it will fuse, andpass into a vapor which causes the intense illumination. The earliest form of electric lighting was by means of the arc, in whichthe light is maintained so long as the electrodes were kept a certaindistance apart. To do this requires delicate mechanism, for the reason that when contactis made, and the current flows through the two electrodes, which areconnected up directly with the coils of a magnet, the cores, orarmatures, will be magnetized. The result is that the electrode, connected with the armature of the magnet, is drawn away from the otherelectrode, and the arc is formed, between the separated ends. As the current also passes through a resistance coil, the moment theends of the electrodes are separated too great a distance, theresistance prevents a flow of the normal amount of current, and thearmature is compelled to reduce its pull. The effect is to cause the twoelectrodes to again approach each other, and in doing so the arc becomesbrighter. It will be seen, therefore, that there is a constant fight between theresistance coil and the magnet, the combined action of the two beingsuch, that, if properly arranged, and with powers in correct relation toeach other, the light may be maintained without undue flickering. Suchdevices are now universally used, and they afford a steady and reliablemeans of illumination. Many improvements are made in this direction, as well as in theingredients of the electrodes. A very novel device for assuring aperfect separation at all times between the electrodes, is by means of apair of parallel carbons, held apart by a non-conductor such as clay, orsome mixture of earth, a form of which is shown in Fig. 116. The drawing shows two electrodes, separated by a non-conductingmaterial, which is of such a character that it will break down andcrumble away, as the ends of the electrodes burn away. [Illustration: _Fig. 116. Parallel Carbons. _] This device is admirable where the alternating current is used, becausethe current moves back and forth, and the two electrodes are thus burnedaway at the same rate of speed. In the direct or continuous current the movement is in one directiononly, and as a result the positive electrode is eaten away twice as fastas the negative. This is the arc form of lamp universally used for lighting large spacesor areas, such as streets, railway stations, and the like. It isimportant also as the means for utilizing searchlight illumination, andfrequently for locomotive headlights. Arc lights are produced by what is called the _series current_. Thismeans that the lamps are all connected in a single line. This isillustrated by reference to Fig. 117, in which A represents the wirefrom the dynamo, and B, C the two electrodes, showing the currentpassing through from one lamp to the next. [Illustration: _Fig. 117. Arc-Lighting Circuit. _] A high voltage is necessary in order to cause the current to leap acrossthe gap made by the separation of the electrodes. THE INCANDESCENT SYSTEM. --This method is entirely different from the arcsystem. It has been stated that certain metals conduct electricity withgreater facility than others, and some have higher resistance thanothers. If a certain amount of electricity is forced through somemetals, they will become heated. This is true, also, if metals, which, ordinarily, will conduct a current freely, are made up into such smallconductors that it is difficult for the current to pass. [Illustration: _Fig 118. Interrupted Conductor. _] In the arc method high voltage is essential; in the incandescent plan, current is the important consideration. In the arc, the light isproduced by virtue of the break in the line of the conductor; in theincandescent, the system is closed at all times. Supposing we have a wire A, a quarter of an inch in diameter, carrying acurrent of, say, 500 amperes, and at any point in the circuit the wireis made very small, as shown at B, in Fig. 118, it is obvious that thesmall wire would not be large enough to carry the current. The result would be that the small connection B would heat up, and, finally, be fused. While the large part of the wire would carry 500amperes, the small wire could not possibly carry more than, say, 10amperes. Now these little wires are the filaments in an electric bulb, and originally the attempt was made to have them so connected up thatthey could be illuminated by a single wire, as with the arc system aboveexplained, one following the other as shown in Fig. 117. [Illustration: _Fig. 119. Incandescent Circuit. _] It was discovered, however, that the addition of each successive lamp, so wired, would not give light in proportion to the addition, but atonly about one-fourth the illumination, and such a course would, therefore, make electric lighting enormously expensive. This knowledge resulted in an entirely new system of wiring up the lampsin a circuit. This is explained in Fig. 119. In this figure A representsthe dynamo, B, B the brushes, C, D the two line wires, E the lamps, andF the short-circuiting wires between the two main conductors C, D. It will be observed that the wires C, D are larger than the cross wiresF. The object is to show that the main wires might carry a very heavyamperage, while the small cross wires F require only a few amperes. This is called the _multiple_ circuit, and it is obvious that the entireamperage produced by the dynamo will not be required to pass througheach lamp, but, on the other hand, each lamp takes only enough necessaryto render the filament incandescent. This invention at once solved the problem of the incandescent system andwas called the subdivision of the electric light. By this means the costwas materially reduced, and the wiring up and installation of lightsmaterially simplified. But the divisibility of the light did not, by any means, solve the greatproblem that has occupied the attention of electricians andexperimenters ever since. The great question was and is to preserve thelittle filament which is heated to incandescence, and from which we getthe light. The effort of the current to pass through the small filament meets withsuch a great resistance that the substance is heated up. If it is madeof metal there is a point at which it will fuse, and thus the lamp isdestroyed. It was found that carbon, properly treated, would heat to a brilliantwhite heat without fusing, or melting, so that this material wasemployed. But now followed another difficulty. As this intense heatconsumed the particles of carbon, owing to the presence of oxygen, meanswere sought to exclude the air. This was finally accomplished by making a bulb of glass, from which theair was exhausted, and as such a globe had no air to support combustion, the filaments were finally made so that they would last a long timebefore being finally disintegrated. The quest now is, and has been, to find some material of a purelymetallic character, which will have a very high fusing point, and whichwill, therefore, dispense with the cost of the exhausted bulb. Somemetals, as for instance, osmium, tantalum, thorium, and others, havebeen used, and others, also, with great success, so that the march ofimprovements is now going forward with rapid strides. VAPOR LAMPS. --One of the directions in which considerable energy hasbeen directed in the past, was to produce light from vapors. The CooperHewitt mercury vapor lamp is a tube filled with the vapor of mercury, and a current is sent through the vapor which produces a greenishlight, and owing to that peculiar color, has not met with much success. It is merely cited to show that there are other directions than the useof metallic conductors and filaments which will produce light, and theday is no doubt close at hand when we may expect some importantdevelopments in the production of light by means of the Hertzian waves. DIRECTIONS FOR IMPROVEMENTS. --Electricity, however, is not a cheapmethod of illumination. The enormous heat developed is largely wasted. The quest of the inventor is to find a means whereby light can beproduced without the generation of the immense heat necessary. Man has not yet found a means whereby he can make a heat withoutincreasing the temperature, as nature does it in the glow worm, or inthe firefly. A certain electric energy will produce both light and heat, but it is found that much more of this energy is used in the heat thanin the light. What wonderful possibilities are in store for the inventor who can makea heatless light! It is a direction for the exercise of ingenuity thatwill well repay any efforts. _Curious Superstitions Concerning Electricity_ Electricity, as exhibited in light, has been the great marvel of alltimes. The word electricity itself comes from the thunderbolt of theancient God Zeus, which is known to be synonymous with the thunderboltand the lightning. Magnetism, which we know to be only another form of electricity, was notregarded the same as electricity by the ancients. Iron which had theproperty to attract, was first found near the town of Magnesia, inLydia, and for that reason was called magnetism. Later on, a glimmer of the truth seemed to dawn on the early scientists, when they saw the resemblance between the actions of the amber and theloadstone, as both attracted particles. And here another curious thingresulted. Amber will attract particles other than metals. The magnet didnot; and from this imperfect observation and understanding, grew abelief that electricity, or magnetism would attract all substances, evenhuman flesh, and many devices were made from magnets, and used as curesfor the gout, and to affect the brain, or to remove pain. Even as early as 2, 500 years before the birth of Christ the Chinese knewof the properties of the magnet, and also discovered that a bar of thepermanent magnet would arrange itself north and south, like themariners' compass. There is no evidence, however, that it was used as amariner's compass until centuries afterwards. But the matter connected with light, as an electrical development, whichinterests us, is its manifestations to the ancients in the form oflightning. The electricity of the earth concentrates itself on the topsof mountains, or in sharp peaks, and accounts for the magnificentelectrical displays always found in mountainous regions. Some years ago, a noted scientist, Dr. Siemens, while standing on thetop of the great pyramid of Cheops, in Egypt, during a storm, noted thatan electrical discharge flowed from his hand when extended toward theheavens. The current manifested itself in such a manner that the hissingnoise was plainly perceptible. The literature of all ages and of all countries shows that thismanifestation of electrical discharges was noted, and became the subjectof discussions among learned men. All these displays were regarded as the bolts of an angry God, andhistorians give many accounts of instances where, in His anger, He sentdown the lightning to destroy. Among the Romans Jupiter thus hurled forth his wrath; and among manyancient people, even down to the time of Charlemagne, any space struckby lightning was considered sacred, and made consecrated ground. From this grew the belief that it was sacrilegious to attempt to imitatethe lightning of the sky--that Deity would visit dire punishment on anyman who attempted to produce an electric light. Virgil relates accountswhere certain princes attempted to imitate the lightning, and werestruck by thunderbolts as punishments. Less than a century ago Benjamin Franklin devised the lightning rod, inorder to prevent lightning from striking objects. The literature of thatday abounds with instances of protests made, on the part of those whowere as superstitions as the people in ancient times, who urged that itwas impious to attempt to ward off Heaven's lightnings. It was arguedthat the lightning was one way in which the Creator manifested Hisdispleasure, and exercised His power to strike the wicked. When such writers as Pliny will gravely set forth an explanation of thecauses of lightning, as follows in the paragraph below, we canunderstand why it inculcated superstitious fears in the people ofancient times. He says: "Most men are ignorant of that secret, which, by close observation ofthe heavens, deep scholars and principal men of learning have foundout, namely, that they are the fires of the uppermost planets, which, falling to the earth, are called lightning; but those especially whichare seated in the middle, that is about Jupiter, perhaps becauseparticipating in the excessive cold and moisture from the upper circleof Saturn, and the immoderate heat of Mars, that is next beneath, bythis means he discharges his superfluity, and therefore it is commonlysaid, 'That Jupiter shooteth and darteth lightning. ' Therefore, like asout of a burning piece of wood a coal flieth forth with a crack, even sofrom a star is spit out, as it were, and voided forth this celestialfire, carrying with it presages of future things; so that the heavensshoweth divine operations, even in these parcels and portions which arerejected and cast away as superfluous. " CHAPTER XVII POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS It would be difficult to mention any direction in human activity whereelectricity does not serve as an agent in some form or manner. Man haslearned that the Creator gave this great power into the hands of man touse, and not to curse. When the dynamo was first developed it did not appear possible that itcould generate electricity, and then use that electricity in order toturn the dynamo in the opposite direction. It all seems so very naturalto us now, that such a thing should practically follow; but man had tolearn this. Let us try to make the statement plain by a few simple illustrations. Bycarefully going over the chapter on the making of the dynamo, it will beevident that the basis of the generation of the current depends on thechanging of the direction of the flow of an electric current. Look at the simple horse-shoe magnet. If two of them are gradually movedtoward each other, so that the north pole of one approaches the northpole of the other, there is a sensible attempt for them to push awayfrom each other. If, however, one of them is turned, so that the northpole of one is opposite the south pole of the other, they will drawtogether. In this we have the foundation physical action of the dynamo and themotor. When power is applied to an armature, and it moves through amagnetic field, the action is just the same as in the case of the handdrawing the north and the south pole of the two approaching magnets fromeach other. The influence of the electrical disturbance produced by that actpermeated the entire winding of the field and armature, and extended outon the whole line with which the dynamo was connected. In this way acurrent was established and transmitted, and with proper wires was sentin the form of circuits and distributed so as to do work. But an electric current, without suitable mechanism, is of no value. Itmust have mechanism to use it, as well as to make it. In the case oflight, we have explained how the arc and the incandescent lamps utilizeit for that purpose. But now, attempting to get something from it in the way of power, meansanother piece of mechanism. This is done by the motor, and this motor issimply a converter, or a device for reversing the action of theelectricity. Attention is called to Figs. 120 and 121. Let us assume that the fieldmagnets A, A are the positives, and the magnets B, B the negatives. Therevolving armature has also four magnet coils, two of them, C, C, beingpositive, and the other two, D, D, negative, each of these magnet coilsbeing so connected up that they will reverse the polarities of themagnets. [Illustration: _Figs. 120-121. _ ACTION OF MAGNETS IN A DYNAMO] Now in the particular position of the revolving armature, in Fig. 120, the magnets of the armature have just passed the respective poles of thefield magnets, and the belt E is compelled to turn the armature past thepole pieces by force in the direction of the arrow F. After the armaturemagnets have gone to the positions in Fig. 121, the positives A try todraw back the negatives D of the armature, and at the same time thenegatives B repel the negatives D, because they are of the samepolarities. This repulsion of the negatives A, B continues until the armature polesC, D have slightly passed them, when the polarities of the magnets C, Dare changed; so that it will be seen, by reference to Fig. 122, that Dis now retreating from B, and C is going away from A--that is, beingforced away contrary to their natural attractive influences, and in Fig. 123, when the complete cycle is nearly finished, the positives are againapproaching each other and the negatives moving together. [Illustration: _Figs. 122-123. _ CYCLE ACTION IN DYNAMO] In this manner, at every point, the sets of magnets are compelled tomove against their magnetic pull. This explains the dynamo. Now take up the cycle of the motor, and note in Fig. 124 that thenegative magnets D of the armature are closely approaching the positiveand negative magnets, on one side; and the positive magnets C arenearing the positive and negatives on the other side. The positives A, therefore, attract the negatives D, and the negative B exert a pull onthe positives C at the same time. The result is that the armature iscaused to revolve, as shown by the dart G, in a direction opposite tothe dart in Fig. 120. [Illustration: _Figs. 124-125. _ ACTION OF MAGNETS IN MOTOR] When the pole pieces of the magnets C, D are about to pass magnets A, B, as shown in Fig. 125, it is necessary to change the polarities of thearmature magnets C, D; so that by reference to Fig. 126, it will be seenthat they are now indicated as C-, and D+, respectively, and have movedto a point midway between the poles A, B (as in Fig. 125), where thepull on one side, and the push on the other are again the same, and thelast Figure 127 shows the cycle nearly completed. The shaft of the motor armature is now the element which turns themechanism which is to be operated. To convert electrical impulses intopower, as thus shown, results in great loss. The first step is to takethe steam boiler, which is the first stage in that source which is themost common and universal, and by means of fuel, converting water intosteam. The second is to use the pressure of this steam to drive anengine; the third is to drive the dynamo which generates the electricalimpulse; and the fourth is the conversion from the dynamo into a motorshaft. Loss is met with at each step, and the great problem is toeliminate this waste. [Illustration: _Figs. 126-127. _ POSITIONS OF MAGNETS IN MOTOR] The great advantage of electrical power is not in utilizing it forconsumption at close ranges, but where it is desired to transmit it forlong distances. Such illustrations may be found in electric railways, and where water power can be obtained as the primal source of energy, the cost is not excessive. It is found, however, that even with the mostimproved forms of mechanism, in electrical construction, the internalcombustion engines are far more economical. _Transmission of Energy_ One of the great problems has been the transmission of the current togreat distances. By using a high voltage it may be sent hundreds ofmiles, but to use a current of that character in the cars, or shops, orhomes, would be exceedingly dangerous. To meet this requirement transformers have been devised, which will takea current of very high voltage, and deliver a current of low tension, and capable of being used anywhere with the ordinary motors. THE TRANSFORMER. --This is an electrical device made up of a core orcores of thin sheet metal, around which is wound sets of insulatedwires, one set being designed to receive the high voltage, and the otherset to put out the low voltage, as described in a former chapter. These may be made where the original output is a very high voltage, sothat they will be stepped down, first from one voltage to a lower, andthen from that to the next lower stage. This is called the "Step down"transformer, and is now used over the entire world, where large voltagesare generated. ELECTRIC FURNACES. --The most important development of electricity in thedirection of heat is its use in furnaces. As before stated, an intenseheat is capable of being generated by the electric current, so that itbecomes the great agent to use for the treatment of refractory material. In furnaces of this kind the electric arc is the mechanical form used toproduce the great heat, the only difference being in the size of theapparatus. The electric furnace is simply an immense form of arc light, capable of taking a high voltage, and such an arc is enclosed within asuitable oven of refractory material, which still further conserves theheat. WELDING BY ELECTRICITY. --The next step is to use the high heat thuscapable of being produced, to fuse metals so that they may be weldedtogether. It is a difficult matter to unite two large pieces of metal bythe forging method, because the highest heat is required, owing to theirbulk, and in addition immense hammers, weighing tons, must be employed. Electric welding offers a simple and easy method of accomplishing theresult, and in the doing of which it avoids the oxidizing action of theforging heat. Instead of heating the pieces to be welded in a forge, asis now done, the ends to be united are simply brought into contact, andthe current is sent through the ends until they are in a soft condition, after which the parts are pressed together and united by the simplemerging of the plastic condition in which they are reduced by the highelectric heat. This form of welding makes the most perfect joint, and requires nohammering, as the mass of the metal flows from one part or end to theother; the unity is a perfect one, and the advantage is that the metalscan be kept in a semi-fluid state for a considerable time, thus assuringa perfect admixture of the two parts. With the ordinary form of welding it is necessary to drive the heatedparts together without any delay, and at the least cooling must bereheated, or the joint will not be perfect. The smallest kinds of electric heating apparatus are now being made, sothat small articles, sheet metal, small rods, and like parts can beunited with the greatest facility. CHAPTER XVIII X-RAY, RADIUM, AND THE LIKE The camera sees things invisible to the human eye. Its most effectivework is done with beams which are beyond human perception. Thephotographer uses the _Actinic_ rays. Ordinary light is composed of theseven primary colors, of which the lowest in the scale is the red, andthe highest to violet. Those below the red are called the Infra-red, and they are the Hertzianwaves, or those used in wireless telegraphy. Those above the violet arecalled Ultra-violet, and these are employed for X-ray work. The formerare produced by the high tension electric apparatus, which we havedescribed in the chapter relating to wireless telegraphy; and thelatter, called also the Roentgen rays, are generated by the Crookes'Tube. This is a tube from which all the atmosphere has been extracted so thatit is a practical vacuum. Within this are placed electrodes so as todivert the action of the electrical discharge in a particular direction, and this light, when discharged, is of such a peculiar character thatits discovery made a sensation in the scientific world. The reason for this great wonder was not in the fact that it projected alight, but because of its character. Ordinary light, as we see it withthe eye, is capable of being reflected, as when we look into a mirror atan angle. The X-ray will not reflect, but instead, pass directly throughthe glass. Then, ordinary light is capable of refraction. This is shown by a ray oflight bending as it passes through a glass of water, which is noticedwhen the light is at an angle to the surface. The X-ray will pass through the water without being changed from astraight line. The foregoing being the case, it was but a simple step toconclude that if it were possible to find a means whereby the human eyecould see within the ultra-violet beam, it would be possible to seethrough opaque substances. From the discovery so important and far reaching it was not long untilit was found that if the ultra-violet rays, thus propagated, weretransmitted through certain substances, their rates of vibration wouldbe brought down to the speeds which send forth the visible rays, and nowthe eye is able to see, in a measure at least, what the actinic raysshow. This discovery was but the forerunner of a still more importantdevelopment, namely, the discovery of _radium_. The actual finding ofthe metal was preceded by the knowledge that certain minerals, andwater, as well, possessed the property of radio-activity. Radio-activity is a word used to express that quality in metals or othermaterial by means of which obscure rays are emitted, that have thecapacity of discharging electrified bodies, and the power to ionizegases, as well as to actually affect photograph plates. Certain metals had this property to a remarkable degree, particularlyuranium, thorium, polonium, actinium, and others, and in 1898 theCuries, husband and wife, French chemists, isolated an element, veryductile in its character, which was a white metal, and had a mostbrilliant luster. Pitchblende, the base metal from which this was extracted, wasdiscovered to be highly radio-active, and on making tests of the producttaken from it, they were surprised to find that it emitted a form ofenergy that far exceeded in calculations any computations made on thebasis of radio-activity in the metals hitherto examined. But this was not the most remarkable part of the developments. Theenergy, whatever it was, had the power to change many other substancesif brought into close proximity. It darkens the color of diamonds, quartz, mica, and glass. It changes some of the latter in color, somekinds being turned to brown and others into violet or purple tinges. Radium has the capacity to redden the skin, and affect the flesh ofpersons, even at some considerable distance, and it is a most powerfulgermicide, destroying bacteria, and has been found also to produce someremarkable cures in diseases of a cancerous nature. The remarkable similarity of the rays propagated by this substance, withthe X-rays, lead many to believe that they are electrical in theircharacter, and the whole scientific world is now striving to use thissubstance, as well as the more familiar light waves of the Roentgentube, in the healing of diseases. It is not at all remarkable that this use of it should first beconsidered, as it has been the history of the electrical developments, from the earliest times, that each successive stage should findadvocates who would urge its virtues to heal the sick. It was so when the dynamo was invented, when the high tension currentwas produced; and electrical therapeutics became a leading theme whentransmission by induction became recognized as a scientific fact. It is not many years since the X-rays were discovered, and the firstannouncement was concerning its wonderful healing powers. This was particularly true in the case of radium, but for some reason, after the first tests, all experimenters were thwarted in theirtheories, because the science, like all others, required infinitepatience and experience. It was discovered, in the case of the X-ray, that it must be used in a modified form, and accordingly, variousmodifications of the waves were introduced, called the _m_ and the _n_rays, as well as many others, each having some peculiar qualification. In time, no doubt, the investigators will find the right quality foreach disease, and learn how to apply it. Thus, electricity, that mostalluring thing which, in itself, cannot be seen, and is of such acharacter that it cannot even be defined in terms which will suit theexact scientific mind, is daily bringing new wonders for ourinvestigation and use. It is, indeed, a study which is so broad that it has no limitations, anda field which never will be exhausted. THE END GLOSSARY OF WORDSUSED IN TEXT OF THIS VOLUME Acid. Accumulator material is sulphuric acid, diluted with water. Active That part of the material in accumulator plates Material. Which is acted upon by the electric current. Accumulator. A cell, generally known as a storage battery, which while it initially receives a charge of electricity, is nevertheless, of such a character, owing to the active material of which it is made, that it accumulates, or, as it were, generates electricity. Aerial Wire, The wire which, in wireless telegraphy, is carried or Conductor. Up into the air to connect the antennę with the receiving and sending apparatus. Alarm, Burglar. A circulating system in a building, connected up with a bell or other signaling means. Alloy. A mixture of two or more metals; as copper and zinc to make brass; nickel and zinc to form German silver. Alternating Current. A current which goes back and forth in opposite directions, unlike a direct current which flows continuously in one direction over a wire. Alternation. The term applied to a change in the direction of an alternating current, the frequency of the alternations ranging up to 20, 000 or more vibrations per second. Amber. A resin, yellow in color, which when rubbed with a cloth, becomes excited and gives forth negative electricity. Ammeter. An instrument for measuring the quantity or flow of electricity. Ampere. The unit of current; the term in which strength of the current is measured. An ampere is an electromotive force of one volt through a resistance of one ohm. Annunciator. A device which indicates or signals a call given from some distant point. Anode. The positive terminal in a conducting circuit, like the terminal of the carbon plate in a battery. It is a plate in an electroplating bath from which the current goes over to the cathode or negative plate or terminal. Arc. A term employed to designate the gap, or the current which flows across between the conductors, like the space between the two carbons of an arc lamp, which gives the light. Armature. A body of iron, or other suitable metal, which is in the magnetic field of a magnet. Armature Bar. The piece which holds the armature. Also one of a series of bars which form the conductors in armature windings. Armature Coil. The winding around an armature, or around the core of an armature. Armature Core. The part in a dynamo or motor which revolves, and on which the wire coils are wound. Astatic (Galvanometer). That which has no magnetic action to direct or divert anything exterior to it. Atom. The ultimate particle of an elementary substance. Attraction. That property of matter which causes particles to adhere, or cohere, to each other. It is known under a variety of terms, such as gravitation, chemical affinity, electro-magnetism and dynamic attraction. Automatic Cut-out. A device which acts through the operation of the mechanism with which it is connected. It is usually applied to a device which cuts out a current when it overcharges or overloads the wire. Bath. In electroplating, the vessel or tank which holds the electroplating solution. Battery. A combination of two or more cells. Battery, Dry. A primary battery in which the electrolyte is made in a solid form. Battery, Galvanic. A battery which is better known by the name of the Voltaic Pile, made up of zinc and copper plates which alternate, and with a layer of acidulated paper between each pair of plates. Battery, Storage. A battery which accumulates electricity generated by a primary battery or a generator. Brush. A term applied to the conducting medium that bears against the cylindrical surface of a commutator. Buzzer. An electric call produced by a rapidly moving armature of an electro-magnet. Cable. A number of wires or conductors assembled in one strand. Candle-power. The amount of light given by the legal-standard candle. This standard is a sperm candle, which burns two grains a minute. Capacity. The carrying power of a wire or circuit, without heating. When heated there is an overload, or the _capacity_ of the wire is overtaxed. Capacity, Storage. The quantity of electricity in a secondary battery when fully charged, usually reckoned in ampere hours. Carbon. A material, like coke, ground or crushed, and formed into sticks or plates by molding or compression. It requires a high heat to melt or burn, and is used as electrodes for arc lamps and for battery elements. It has poor conductivity, and for arc lamps is coated with copper to increase its conductivity. Cell, Electrolytic. A vessel containing an electrolyte for electroplating purposes. Charge. The quantity of electricity on the surface of a body or conductor. Chemical Change. When a current passes through electrodes in a solution, a change takes place which is chemical in its character. Adding sulphuric acid to water produces heat. If electrodes of opposite polarity are placed in such an acid solution, a chemical change is produced, which is transformed into electricity. Choking Coil. An instrument in a circuit which by a form of resistance regulates the flow of the current, or returns part of it to the source of its generation. Counter-electromotive Force. Cells which are inserted in opposition to a battery to reduce high voltage. Circuit, Astatic. A circuit in an instrument so wound that the earth's magnetism will not affect it. Circuit Breaker. Any instrument in a circuit which cuts out or interrupts the flow of a current. Circuit, External. A current flows through a wire or conductor, and also along the air outside of the conductor, the latter being the _external circuit. _ Circuit Indicator. An instrument, like a galvanometer, that shows the direction in which a current is flowing through a conductor. Circuit, Return. Usually the ground return, or the negative wire from a battery. Circuit, Short. Any connection between the mains or parallel lines of a circuit which does not go through the apparatus for which the circuit is intended. Coherer. A tube, or other structure, containing normally high resistance particles which form a path or bridge between the opposite terminals of a circuit. Coil. A wire, usually insulated, wound around a spool. Coil, Induction. One of a pair of coils designed to change the voltage of a current of electricity, from a higher to a lower, or from a lower to a higher electro-motive force. Coil, Resistance. A coil so wound that it will offer a resistance to a steady current, or reduce the flow of electricity. Commutator. A cylinder on the end of the armature of a dynamo or motor and provided with a pair of contact plates for each particular coil in the armature, in order to change the direction of the current. Compass. An apparatus which indicates the direction or flow of the earth's magnetism. Condenser. A device for storing up electro-static charges. Conductance. That quality of a conductor to carry a current of electricity, dependent on its shape for the best results. Conduction. The transmission of a current through a rod, wire or conductor. Conductivity. That quality which has reference to the capacity to conduct a current. Conductor. Any body, such as a bar, rod, wire, or machine, which will carry a current. Connector. A binding post, clamp, screw, or other means to hold the end of a wire, or electric conductor. Contact. To unite any parts in an electric circuit. Controller. The handle of a switchboard, or other contact making and breaking means in a circuit. Converter. An induction coil in an alternating circuit for changing potential difference, such as high alternating voltage into low direct current voltage. Convolution. To wind like a clock spring. Core. The inner portion of an electro-magnet. The inside part of an armature wound with wire. Core, Laminated. When the core is built up of a number of separate pieces of the same material, but not insulated from each other. Coulomb. The unit of electrical quantity. It is the quantity passed by a current of one ampere intensity in one second of time. Couple, Electric. Two or more electrodes in a liquid to produce an electric force. Current, Alternating. A natural current produced by the action of electro-magnets. It is a succession of short impulses in opposite directions. Current, Constant. A current which is uniformly maintained in a steady stream. Current, Induced. A current produced by electro-dynamic induction. Current Meter. An apparatus for indicating the strength of a current. An ammeter. Current, Oscillating. A current which periodically alternates. Current, Periodic. A periodically varying current strength. Current, Undulating. A current which has a constant direction, but has a continuously varying strength. Decomposition. The separation of a liquid, such as an electrolyte, into its prime elements, either electrically or otherwise. Deflection. The change of movement of a magnetic needle out of its regular direction of movement. Demagnetization. When a current passes through a coil wound on an iron core, the core becomes magnetized. When the current ceases the core is no longer a magnet. It is then said to be _demagnetized_. It also has reference to the process for making a watch non-magnetic so that it will not be affected when in a magnetic field. Density. The quantity of an electric charge in a conductor or substance. Depolarization. The removal of magnetism from a permanent magnet, or a horse-shoe magnet, for instance. It is generally accomplished by applying heat. Deposition, The act of carrying metal from one pole of a cell to Electrolysis. Another pole, as in electroplating. Detector. Mechanism for indicating the presence of a current in a circuit. Diaphragm. A plate in a telephone, which, in the receiver, is in the magnetic field of a magnet, and in a transmitter carries the light contact points. Dielectric. A non-conductor for an electric current, but through which electro-static induction will take place. For example: glass and rubber are dielectrics. Discharge. The current flowing from an accumulator. Disintegration. The breaking up of the plate or active material. Disruptive. A static discharge passing through a dielectric. Duplex Wire. A pair of wires usually twisted together and insulated from each other to form the conducting circuit of a system. Dynamic Electricity. The term applied to a current flowing through a wire. Dynamo. An apparatus, consisting of core and field magnets, which, when the core is turned, will develop a current of electricity. Earth Returns. Instead of using two wires to carry a circuit, the earth is used for what is called the _return_ circuit. Efficiency. The total electrical energy produced, in which that wasted, as well as that used, is calculated. Elasticity. That property of any matter which, after a stress, will cause the substance to return to its original form or condition. Electricity has elasticity, which is utilized in condensers, as an instance. Electricity, Lightning, and, in short, any current or electrical Atmospheric. Impulse, like wireless telegraphic waves, is called _atmospheric_. Electricity, Electricity with a low potentiality and large current Voltaic. Density. Electrification. The process of imparting a charge of electricity to any body. Electro-chemistry. The study of which treats of electric and chemical forces, such as electric plating, electric fusing, electrolysis, and the like. Electrode. The terminals of a battery, or of any circuit; as, for instance, an arc light. Electrolyte. Any material which is capable of being decomposed by an electric current. Electro-magnetism. Magnetism which is created by an electric current. Electrometer. An instrument for measuring static electricity, differing from a galvanometer, which measures a current in a wire that acts on the magnetic needle of the galvanometer. Electro-motive Voltage, which is the measure or unit of e. M. F. Force. (E. M. F. ) Electroscope. A device for indicating not only the presence of electricity, but whether it is positive or negative. Electro-static Surfaces separated by a dielectric for opposite Accumulator. Charging of the surface. Element. In electricity a form of matter, as, for instance, gold, or silver, that has no other matter or compound. Original elements cannot be separated, because they are not made up of two or more elements, like brass, for instance. Excessive Charge. A storage battery charged at too high a rate. Excessive Discharge. A storage battery discharged at too high a rate. Excessive Overcharge. Charging for too long a time. Exciter. A generator, either a dynamo or a battery, for exciting the field of a dynamo. Exhaustive Discharge. An excessive over-discharge of an accumulator. F. The sign used to indicate the heat term Fahrenheit. Fall of Voltage. The difference between the initial and the final voltage in a current. Field. The space or region near a magnet or charged wire. Also the electro-magnets in a dynamo or motor. Flow. The volume of a current going through a conductor. Force, Electro-magnetic. The pull developed by an electro-magnet. Frictional A current produced by rubbing dissimilar Electricity. Substances together. Full Load. The greatest load a battery, accumulator or dynamo will sustain. Galvanic. Pertaining to the electro-chemical relations of metals toward each other. Galvanizing. The art of coating one metal with another, such, for instance, as immersing iron in molten zinc. Galvanometry. An instrument having a permanently magnetized needle, which is influenced by a coil or a wire in close proximity to it. Galvanoscope. An instrument, like a galvanometer, which determines whether or not a current is present in a tested wire. Generator. A term used to generally indicate any device which originates a current. German Silver. An alloy of copper, nickel and zinc. Graphite. One form of carbon. It is made artificially by the electric current. Grid. The metallic frame of a plate used to hold the active material of an accumulator. Gravity. The attraction of mass for mass. Weight. The accelerating tendency of material to move toward the earth. Gutta Percha. Caoutchouc, which has been treated with sulphur, to harden it. It is produced from the sap of tropical trees, and is a good insulator. Harmonic Receiver. A vibrating reed acted on by an electro-magnet, when tuned to its pitch. High E. M. F. A term to indicate currents which have a high voltage, and usually low amperage. Igniter. Mechanism composed of a battery, induction coil and a vibrator, for making a jump spark, to ignite gas, powder, etc. I. H. P. Abbreviation, which means Indicated Horse Power. Impulse. A sudden motion of one body acting against another. An electro-magnetic wave magnetizing soft iron, and this iron attracting another piece of iron, as an example. Incandescence, A conductor heated up by a current so it will Electric. Glow. Induced Current. A current of electricity which sets up lines of force at right angles to the body of the wire through which the current is transmitted. Induction, Magnetic. A body within a magnetic field which is excited by the magnetism. Installation. Everything belonging to an equipment of a building, or a circuiting system to do a certain thing. Insulation. A material or substance which resists the passage of a current placed around a conductor. Intensity. The strength of a magnetic field, or of a current flowing over a wire. Internal Resistance. The current strength of electricity of a wire to resist the passage. Interrupter. A device in a wire or circuit for checking a current. It also refers to the vibrator of an induction coil. Joint. The place where two or more conductors are united. Joint Resistance. The combined resistance offered by two or more substances or conductors. Jump Spark. A spark, disruptive in its character, between two conducting points. Initial Charge. The charge required to start a battery. Kathode, or Cathode. The negative plate or side of a battery. The plate on which the electro deposit is made. Key. The arm of a telegraph sounder. A bar with a finger piece, which is hinged and so arranged that it will make and break contacts in an electric circuit. Keyboard. A switch-board; a board on which is mounted a number of switches. Kilowatt. A unit, representing 1, 000 watts. An electric current measure, usually expressed thus: K. W. Kilowatt Hour. The computation of work equal to the exertion of one kilowatt in one hour. Knife Switch. A bar of a blade-like form, adapted to move down between two fingers, and thus establish metallic connections. Laminated. Made up of thin plates of the same material, laid together, but not insulated from each other. Lamp Arc. A voltaic arc lamp, using carbon electrodes, with mechanism for feeding the electrodes regularly. Lamp, Incandescent. A lamp with a filament heated up to a glow by the action of an electric current. The filament is within a vacuum in a glass globe. Leak. Loss of electrical energy through a fault in wiring, or in using bare wires. Load. The ampere current delivered by a dynamo under certain conditions. Low Frequency. A current in which the vibrations are of few alternations per second. Magnet. A metallic substance which has power to attract iron and steel. Magnet Bar. A straight piece of metal. Magnet Coil. A coil of wire, insulated, surrounding a core of iron, to receive a current of electricity. Magnet Core. A bar of iron adapted to receive a winding of wire. Magnet, Field. A magnet in a dynamo. A motor to produce electric energy. Magnet, Permanent. A short steel form, to hold magnetism for a long time. Magnetic Adherence. The adherence of particles to the poles of a magnet. Magnetic That quality of a metal which draws metals. Also Attraction and the pulling action of unlike poles for each Repulsion. Other, and pushing away of like poles when brought together. Magnetic Force. The action exercised by a magnet of attracting or repelling. Magnetic Pole. The earth has North and South magnetic poles. The south pole of a magnetic needle is attracted so it points to the north magnetic pole; and the north pole of the needle is attracted to point to the south magnetic pole. Magneto-generator. A permanent magnet and a revolving armature for generating a current. Maximum Voltage. The final voltage after charging. Molecule. Invisible particles made up of two or more atoms of different matter. An atom is a particle of one substance only. Morse Sounder. An electric instrument designed to make a clicking sound, when the armature is drawn down by a magnet. Motor-dynamo. A motor and a dynamo having their armatures connected together, whereby the motor is driven by the dynamo, so as to change the current into a different voltage and amperage. Motor-transformer. A motor which delivers the current like a generator. Needle. A bar magnet horizontally poised on a vertical pivot point, like the needle of a mariner's compass. Negative Amber, when rubbed, produces negative electricity. Electricity. A battery has positive as well as negative electricity. Negative Element. That plate in the solution of a battery cell which is not disintegrated. Normal. The usual, or ordinary. The average. In a current the regular force required to do the work. North Pole, The term applied to the force located near Electric. The north pole of the globe, to which a permanent magnet will point if allowed to swing freely. O. Abbreviation for Ohm. Ohm. The unit of resistance. Equal to the resistance of a column of mercury one square millimeter in cross section, and 106. 24 centimeters in length. Ohm's Law. It is expressed as follows: 1. The current strength is equal to the electro-motive force divided by its resistance. 2. The electro-motive force is equal to the current strength multiplied by the resistance. 3. The resistance is equal to the electro-motive force divided by the current strength. Overload. In a motor an excess of mechanical work which causes the armature to turn too slowly and produces heat. Phase. One complete oscillation. The special form of a wave at any instant, or at any interval of time. Plate, Condenser. In a static machine it is usually a plate of glass and revoluble. Plate, Negative. The plate in a battery, such as carbon, copper or platinum, which is not attacked by the solution. Plating, Electro-. The method of coating one metal with another by electrolysis. Polarity. The peculiarity, in a body, of arranging itself with reference to magnetic influence. Parallel. When a number of cells are coupled so that their similar poles are grouped together. That is to say, as the carbon plates, for instance, are connected with one terminal, and all the zinc plates with the other terminal. Polarization. When the cell is deprived of its electro-motive force, or any part of it, polarization is the result. It is usually caused by coating of the plates. Porosity. Having small interstices or holes. Positive Current. One which deflects a needle to the left. Positive Any current flowing from the active element, Electricity. Such as zinc, in a battery. The negative electricity flows from the carbon to the zinc. Potential, Electric. The power which performs work in a circuit. Potential Energy. That form of force, which, when liberated, does or performs work. Power Unit. The volt-amperes or watt. Primary. The induction coil in induction machines, or in a transformer. Push Button. A thumb piece which serves as a switch to close a circuit while being pressed inwardly. Quantity. Such arrangement of electrical connections which give off the largest amount of current. Receiver. An instrument in telephony and telegraphy which receives or takes in the sound or impulses. Relay. The device which opens or closes a circuit so as to admit a new current which is sent to a more distant point. Repulsion, That tendency in bodies to repel each other when Electric. Similarly charged. Resilience. The springing back to its former condition or position. Electricity has resilience. Resistance. The quality in all conductors to oppose the passage of a current. Resistance Coil. A coil made up of wire which prevents the passage of a current to a greater or less degree. Resistance, The counter force in an electrolyte which seeks Electrolytic. To prevent a decomposing current to pass through it. Resistance: Internal, The opposing force to the movement of a current External. Which is in the cell or generator. This is called the _internal_. That opposite action outside of the cell or generator is the _external_. Resonator, An open-circuited conductor for electrically Electric. Resounding or giving back a vibration, usually exhibited by means of a spark. Rheostat. A device which has an adjustable resistance, so arranged that while adjusting the same the circuit will not be open. Safety Fuse. A piece of fusible metal of such resistance that it breaks down at a certain current strength. Saturated. When a liquid has taken up a soluble material to the fullest extent it is then completely saturated. Secondary. One of the two coils in a transformer, or induction coil. Secondary Plates. The brown or deep red plates in a storage battery when charged. Self-excited. Producing electricity by its own current. Series. Arranged in regular order. From one to the other directly. If lamps, for instance, should be arranged in circuit on a single wire, they would be in series. Series, Multiple. When lamps are grouped in sets in parallel, and these sets are then connected up in series. Series Windings. A generator or motor wound in such a manner that one of the commutator brush connections is joined to the field magnet winding, and the other end of the magnet winding joined to the outer circuit. Shunt. Going around. Shunt Winding. A dynamo in which the field winding is parallel with the winding of the armature. Snap Switch. A switch so arranged that it will quickly make a break. Sounder. The apparatus at one end of a line actuated by a key at the other end of the line. Spark Coil. A coil, to make a spark from a low electro-motive force. Spark, Electric. The flash caused by drawing apart the ends of a conductor. Specific Gravity. The weight or density of a body. Static Electricity. Generated by friction. Also lightning. Any current generated by a high electro-motive force. Strength of Current. The quantity of electricity in a circuit. Synchronize. Operating together; acting in unison. Terminal. The end of any electric circuit or of a body or machine which has a current passing through it. Thermostat, Electric. An electric thermometer. Usually made with a metal coil which expands through the action of the electricity passing through it, and, in expanding, it makes a contact and closes a circuit. Transformer. The induction coil with a high initial E. M. F. Changes into a low electro-motive force. Unit. A standard of light, heat, electricity, or of other phenomena. Vacuum. A space from which all matter has been exhausted. Vibrator. Mechanism for making and breaking circuits in induction coils or other apparatus. Volt. The unit of electro-motive force. Voltage. Electro-motive force which is expressed in volts. Voltaic. A term applied to electric currents and devices. Volt-meter. An apparatus for showing the difference of potential, or E. M. F. In the term of volts. Watt. The unit of electrical activity. The product of amperes multiplied by volts. Watt Hour. One watt maintained through one hour of time. Waves, Electric Waves in the ether caused by electro-magnetic Magnetic. Disturbances. X-rays. The radiation of invisible rays of light, which penetrate or pass through opaque substances. Yoke, or Bar. A soft iron body across the ends of a horseshoe magnet, to enable the magnet to retain its magnetism an indefinite time. Zinc Battery. A battery which uses zinc for one of its elements. INDEX A Accumulated, 31. Accumulation, 29. Accumulator cell, 87. Accumulators, 82, 88, 89. Accumulators, plates, 83. Acid, 34, 37, 125. Acid maker, 125. Acid, sulphuric, 31, 84. Acidulated, 55. Acidulated water, 34. Acoustics, 110. Actinic rays, 184, 185. Actinium, 186. Active element, 82. Adjustable rod, 107. Adjusting screw, 70, 71, 72, 73, 106. Aerial wire, 108. Agents, 13, 32. Alarms, burglar, 11, 76, 80. Alkali, 125. Alkaline, 37. Alternate, 127. Alternating, 38, 149, 150, 153, 154, 155, 156. Alternating current, 145. Alternating periods, 149. Alternations, 147. Aluminum, 128, 129, 135, 137. Aluminum hydrate, 129. Amber, 5, 171. Ammeter, 7, 88. Amperage, 38, 61, 62, 132, 159, 160, 168. Ampere, 7, 37, 60, 63, 139, 140, 167. Amplitude, 111. Annunciator, 65, 74, 76, 79, 80, 81. Annunciator bells, 11. Anode, 35, 133, 134. Antennę, 108. Antimony 137, 143. Anvil, 13, 14. Apparatus, 11, 57, 106, 139, 145. Arc, 163, 182. Arc lighting, 38, 165. Arc system, 166. Armature, 18, 25, 38, 40, 42, 43, 45, 46, 47, 48, 53, 55, 70, 72, 73, 74, 90, 93, 112, 151, 152, 155, 163, 176, 177, 178, 179, 180. Armature brush, 48. Armature post, 71. Armature, vertical, 75. Armature winding, 42, 43, 156. Asbestos, 140. Astatic galvanometer, 108. Atmosphere, 184. Attract, 30. Attracted, 72. Attraction, 21, 25. Attractive, 178. Automatic, 120. Auxiliary, 44. Awls, 14. B Bacteria, 126, 187. Bar, cross, 66. Bar, horizontal, 46. Bar, parallel switch, 67. Bar, switch, 65, 68. Base block, 66. Batteries, 11, 93, 122. Battery, 29, 30, 32, 35, 36, 46, 47, 80, 81, 82, 83, 85, 86, 88, 92, 94, 95, 107, 108, 116, 117, 118, 121, 134, 142. Battery charging, 82. Bearings, 45, 46. Bells, 65, 73, 76, 122. Bells, electric, 70. Bench, 13, 15, 17. Binding post, 52, 70, 71, 72, 103, 107, 108, 121. Binding screw, 65, 66. Bismuth, 18, 143. Bit, 13. Blue vitriol, 57. Brass plate, 77, 78. Brazing, 17, 65. Bridge, 52. Brush holder, 46. Brushes, 48, 150, 151, 153, 167. Burglar, 11. Burglar alarm, 76, 80. Buttons, contact, 80. Buttons, push, 65, 68, 69, 70, 76, 79. C Calorimeter, 56. Cancerous, 187. Candle power, 89, 139. Cap, removable, 73. Cap screws, 42. Carbon, 35, 119, 121, 162, 163, 169. Carbon block, 120. Carbon pencil, 119. Cathode, 35, 36, 133, 134. Cell, 29, 33. Cell, accumulator, 87. Cell, charging, 87. Channel, 43. Channel, concave, 40. Charged, 120. Charged battery, 82. Charging circuit, 82, 89. Charging source, 83. Charged wire, 147. Chemical, 57. Chisels, 13. Chloride of lime, 84. Choked, 157. Choking coils, 145, 146, 156, 158. Circuit, 33, 69, 73, 76, 78, 80, 81, 90, 92, 93, 109, 113, 116, 121, 122, 131, 134, 143, 156. Circuit, primary, 99. Circuit, secondary, 99. Circuiting, 81, 155. Circuiting system, 79. Clapper arm, 70. Closed rings, 26. Coherer, 105, 108, 109. Cohering, 106. Coils, 18, 26, 52, 55, 74, 160. Coils, choking, 145, 146, 156, 158. Coils, induction, 99, 102. Coils, primary, 109. Coils, secondary, 102, 109. Coincide, 42. Cold, 14. Collecting surfaces, 30. Collector, 31. Column, 61. Combustion, 169. Commutator, 44, 46, 151, 152. Commutator brushes, 46. Commutator plates, 45. Compass, 22, 24, 172. Composition, 83, 124. Compound wound, 47. Concave channel, 40. Condenser, 98, 100, 101, 102, 108. Conduct, 6, 108. Conduction, 135, 136, 138, 166, 170. Conduction current, 27. Conductor, 21, 31, 33, 63, 98, 116, 161, 162. Conduit, 72. Conically formed, 126. Conjunction, 143. Connecting wire, 58. Connection, 72, 76. Construction, magnet, 39. Consumption, 180. Contact, 122, 123, 152, 162. Contact finger, 150. Contact plate, 67, 68, 79. Contact screws, 93. Contact surface, 66. Continuous, 145. Converter, 176. Converting, 142, 145, 146. Copper, 18, 34, 36, 65, 66, 132, 133, 134, 135, 136, 137, 142, 143. Copper cyanide, 133. Copper plate, 33, 35, 58, 67. Copper sulphate, 57. Copper voltameter, 55, 57. Core, 27, 28, 36, 39, 40, 115. Core, magnet, 75, 93. Counter, clock-wise, 51. Coupled, 36. Crank, 30. Crookes' tube, 184. Cross bar, 52, 66. Crown of cups, 32. Crystal, 85. Current, 6, 7, 13, 18, 26, 27, 28, 35, 36, 37, 38, 47, 50, 51, 52, 55, 56, 57, 58, 59, 62, 63, 70, 72, 73, 90, 95, 98, 105, 108, 116, 133, 134, 135, 136, 138, 139, 140, 141, 142, 143, 147, 148, 149, 150, 152, 153, 157, 160, 161, 163, 165, 166, 170. Current, alternating, 150. Current changing, 82. Current conduction, 27. Current, continuous, 164. Current, direct, 145, 150. Current direction, 50. Current, exterior, 50, 150. Current, reversing, 148. Current strength, 7, 57. Current testing, 143. Cut-out, 120. Cutter, 14. Cutting, lines of force, 38. Cylinder, 44. Cylindrical, 43. D Dash, 95, 97. Decoherer, 106, 108. Decomposed, 57, 128. Decomposes, 55. Decomposing, 123. Decomposition, 12, 35, 82. Deflected, 54. Degree, 135, 162. Demagnetized, 24, 72. Deposited, 58, 133. Depression, 15, 140. Detecting current, 49. Detector, 49, 52, 54, 105. Devices, measuring, 27. Diagrams, 46, 48, 79, 89. Diagrammatically, 81. Diamagnetic, 19. Diametrically, 114. Diaphragm, 112, 113, 116, 120, 122. Diamonds, 186. Diluted, 86. Direct current, 38, 140. Direction of current, 50. Direction of flow, 98. Discharge, 172. Disintegrate, 132. Disk, 43. Dissimilar, 37. Disturbance, 176. Dividers, 14. Divisibility, 168. Dot, 96, 97. Dot and dash, 96. Double click, 95. Double line, 65. Double-pole switch, 65. Double-throw switch, 117. Drawing, 20. Drill, ratchet, 13. Drops, 81. Ductile, 186. Duplex wire, 115. Dynamo, 7, 27, 38, 42, 46, 48, 62, 82, 83, 87, 89, 132, 141, 142, 145, 150, 155, 161, 165, 167, 175, 176, 180, 187. Dynamo fields, 40, 41. E Earth, 22. Elasticity, 100, 142. Electric, 6, 31, 49, 50, 76, 78, 81, 131, 142, 158, 162, 173, 176. Electric arc, 63, 163. Electric bell, 19, 69, 70, 71, 72, 106, 117. Electric bulbs, 167. Electric circuit, 118. Electric fan, 55. Electric field, 76. Electric hand purifier, 129. Electric heating, 135, 137, 161. Electric iron, 130, 141. Electric lamp socket, 139. Electric light, 56, 66. Electric lighting, 161. Electric power, 113. Electric welding, 183. Electrical, 8, 11, 65, 96, 98, 104, 141, 159, 180, 184, 187. Electrical impulses, 105, 147, 148. Electrical manifestations, 175. Electrically, 32, 70. Electricity, 5, 6, 7, 8, 9, 12, 13, 18, 21, 26, 27, 28, 29, 38, 49, 54, 60, 61, 62, 82, 97, 98, 100, 104, 110, 112, 116, 123, 124, 133, 134, 136, 138, 145, 146, 147, 154, 156, 160, 166, 170, 171, 172, 175, 182, 187. Electricity measuring, 49. Electricity, thermo-, 142. Electrified, 37, 186. Electro-chemical, 55. Electrode, 35, 124, 127, 128, 161, 162, 163, 164, 165, 184. Electrolysis, 7, 123, 126, 132. Electrolyte, 33, 35, 36, 57, 86, 88, 123, 132, 142. Electrolytic, 55, 123, 125. Electro-magnet, 59, 78. Electro-magnetic, 7, 24, 25, 29, 37, 55, 92, 93, 94. Electro-magnetic force, 7. Electro-magnetic rotation, 7. Electro-magnetic switch, 116. Electro-meter, 7. Electro-motive force, 37, 63, 99. Electroplate, 12, 38, 48, 123, 132, 134. Electro-positive-negative, 142, 143. Elements, 36, 83. Engine energy, 170, 180. Equidistant, 127. Ether, 104. Example, 61. Excited, 47. Extension plate, 103. Exterior, 3. Exterior magnetic, 27. External, 37. External circuit, 153. External current, 50. External resistance, 37. F Factor, 61. Ferrous oxide, 125. Field, 46, 47. Field, dynamo, 40, 41. Field magnet cores, 155. Field, magnetic, 38. Field of force, 33. Field wire, 48. Filament, 168, 169, 170. Filter, 128. Flat iron, 140. Flocculent, 128. Force, 50. Formulated, 19. Friction, 32. Frictional, 6, 7, 29. Fuse, 169. G Galvani, 7. Galvanic, 7, 23, 30. Galvanometer, 7, 49, 108, 143. Galvanoscope, 55, 58, 59. Gaseous, 128. Gasoline, 99. Gas stove, 17. Gelatine, 128. Generate, 29, 38, 134, 136, 145. Generated, 55. Generating, 32, 134. Generation, 170. Generator, 32, 125, 147. German silver, 136, 137. Germicide, 187. Gimlets, 17. Glass, 30, 86, 126, 186. Gold, 135. Grid, 84. Ground circuit, 121. Gunpowder, 6. H Hack-saw, 14. Hammer, 13. Heart-shaped switch, 77. Heater, 136. Heating, 13, 38. Hertzian rays, 170. Hertzian wave, 184. High tension, 38, 102, 184. High tension apparatus, 98. High tension coils, 103. High voltage, 158. Horizontal bar, 46. Horseshoe magnet, 22, 24, 175. Hydrate of aluminum, 129. Hydrogen, 35, 123, 125, 128. I Igniting, 99. Illumination, 162, 163, 165, 167, 170. Immersed, 133. Impulses, 60, 62, 96, 104, 109, 152, 179. Incandescent, 166, 168. Induced, 28. Inductance, 149, 150. Induction, 27, 37, 98, 147. Induction coils, 99, 102, 106. Influences, 178. Initial charge, 88. Insulated, 27, 28, 40, 43, 52, 55, 73, 115, 151, 180. Insulating, 66, 69, 120, 140, 164. Insulating material, 114. Insulation, 40, 116. Instruments, 49, 94, 112, 118, 120. Instruments, measuring, 8. Intensity, 55, 60, 104, 154. Interior, magnetic, 23. Internal resistance, 37. Interruption, 102, 103. Installation, 168. Ionize, 186. Iron, 19, 132, 133, 136, 142, 171. Isolated, 186. J Jar, 29, 31, 32. Journal, 46. Journal block, 16, 146. Jump spark, 99. K Key, 90, 91, 95. Key, sending, 90. Knob, 32. Knob, terminal, 31. L Laboratory, 9. Lead, 31, 136. Lead, precipitated, 83, 85. Lead, red, 83, 84. Lever switching, 67. Light, 104. Light method, 56. Lighting, 9, 38. Lighting circuit, 48. Lighting system, 82. Lightning, 6, 171, 172, 173. Lightning rod, 173. Lime, chloride of, 84. Line of force, 146. Line wire, 122. Line, magnetic, 22, 23. Liquid, 32. Litharge, 83. Loadstone, 17. Locomotives, 165. Low tension, 38, 98, 102, 179. M Magnet bar, 20. Magnet core, 16, 75, 93. Magnet, electro, 59, 78. Magnet, horseshoe, 22, 25, 175. Magnet lines, 22, 23. Magnet, permanent, 25, 38, 46, 50, 172. Magnet, reversed, 20. Magnet, steel, 53. Magnet, swinging, 53. Magnetic, 7, 19, 20, 21, 22, 25, 113, 178. Magnetic construction, 39. Magnetic exterior, 27. Magnetic field, 22, 24, 27, 38, 50, 112, 146, 148, 155. Magnetic interior, 23. Magnetic pull, 59. Magnetic radiator, 37. Magnetism, 19, 54, 104, 110, 159, 171. Magnetized, 18, 25, 27, 50. Magnetized wire, 146. Magnets, 13, 14, 18, 19, 20, 21, 22, 23, 24, 25, 39, 51, 53, 54, 70, 71, 73, 75, 81, 90, 93, 112, 113, 115, 147, 150, 163, 176, 177, 178. Main conductor, 31. Mandrel, 15, 16. Manganese, 19. Manifestations, 19. Mariner, 172. Material, non-conducting, 90. Maximum, 154. Measure, 55, 56, 60, 62. Measurement, 62. Measuring devices, 27. Measuring instruments, 8. Mechanism, 47, 180. Medical batteries, 99. Mercury, 63, 169. Metal base, 73. Mica, 186. Microphone, 118, 119, 120. Millimeter, 63. Minus, 34. Minus sign, 21. Morse code, 76. Motor, 7, 21, 27, 46, 47, 62, 82, 99, 150, 176, 180. Mouthpiece, 115. Mouthpiece rays, 188. Moving field, 117. Multiple, 168. Musical scale, 111. N Negative, 21, 35, 36, 68, 83, 86, 87, 94, 125, 151, 152, 154, 165, 177, 178, 179. Neutral, 125. Neutral plate, 84. Nickel, 136. Nickel plating, 132. Nitrate of silver, 62. Nitrogen, 126. Non-conducting material, 90. Non-conductor, 164. Non-magnetic, 19. North pole, 20, 21, 22, 23, 25, 50, 54, 156. Number plate, 75. N-ray, 188. O Ohms, 60, 63. Ohms, international, 63. Ohms law, 7. Operator, 95, 118. Oscillating, 99, 105. Osmium, 169. Oxides, 125. Oxidizing, 183. Oxygen, 35, 123, 125, 126, 128, 129, 169. P Packing ring, 124. Paraffine, 56, 100, 101, 102. Paraffine wax, 86. Parallel, 87, 88, 89. Parallel switch bar, 67. Parallel wires, 28, 49. Partition, 124. Peon, 13. Percolate, 128. Periodicity, 159. Periods of alternations, 149. Permanent, 18, 19, 50. Permanent magnet, 25, 38, 46, 50, 172. Phase, 19. Phenomenon, 27, 65. Photograph, 186. Physical, 21. Pile, voltaic, 33. Pipe, 61. Pitchblende, 186. Pivot pin, 53. Pivotal, 22. Plane, 13. Plate, 57, 93. Plate, contact, 67, 68, 79. Plate, copper, 33, 35, 58, 67. Plate, negative, 84. Plate, number, 75. Plate, positive, 84, 88. Plate, zinc, 33. Platinum, 13, 57, 137. Pliers, 14. Plus sign, 21, 24. Pointer, 53. Polarity, 154, 177, 178, 179. Polarization, 35. Pole, north, 20, 21, 22, 23, 25, 50, 54, 156. Pole piece, 40, 42. Pole, south, 20, 21, 22, 25, 50, 54, 156. Poles, 177, 179. Polonium, 186. Porcelain, 86. Porous, 85. Positive, 4, 21, 25, 36, 40, 68, 83, 86, 87, 94, 123, 125, 151, 152, 153, 155, 165. Post, binding, 52, 71. Potentiality, 105, 109. Power, 38, 186. Power, candle, 89, 139. Precipitate of lead, 83, 85. Precision, 7. Pressure, 87. Primary, 35, 62, 98, 134, 142, 159, 184. Primary battery, 7, 99. Primary circuit, 99. Primary coil, 106, 109. Prime conductor, 6. Projected, 185. Propagated, 105, 185. Properties, 55. Purification, 123, 128. Purifier, 126, 131. Push button, 65, 68, 69, 70, 76, 79. Q Quantity, 55, 60, 61, 138. Quartz, 186. R Radio-activity, 186. Radium, 184, 185, 187, 188. Ratchet drill, 13. Reaction, 148. Receiver, 12, 90, 97, 121, 122. Receiving station, 109. Rectangular, 69. Rectifiers, 146. Red lead, 83, 84. Reel, 13. Reflected, 185. Refraction, 185. Refractory, 182. Register, 57. Removable, 54. Removable cap, 73. Repel, 20. Repulsion, 21, 128. Reservoir, 61, 62. Resiliency, 99. Resistance, 7, 36, 37, 60, 63, 99, 135, 136, 137, 138, 140, 141, 156, 157, 163, 166, 168. Resistance bridge, 7. Resistance, external, 37. Resistance, internal, 37. Rheostat, 7. Reversed, 20, 50, 153. Reversible, 163. Reversing, 176. Reversing switch, 67. Revolubly, 46. Revolve, 179. Revolving, 177. Roentgen rays, 184. Roentgen tube, 187. Rotation, 149. Rubber, 40, 46, 77, 115, 126, 130, 138. S Sad-irons, 13. Saline, 133. Sanitation, 12. Saturated, 85. Screw, 15. Screw, binding, 65, 66. Screw-driver, 14. Screw, set, 72. Sealing wax, 53. Secondary, 62, 98, 105, 158, 159, 160. Secondary circuit, 99. Secondary coil, 107, 108. Self-induction, 149, 156. Sender, 90, 97. Sending apparatus, 106. Sending key, 90. Separately excited, 46. Series-wound, 47. Severed magnet, 20. Sewage, 12. Shaft, 30. Shears, 14, 17. Shellac, 40. Shunt-wound, 47. Signal, 118. Silver, 19, 63, 125. Silver nitrate, 62. Socket, 54, 139. Soldering, 14. Soldering iron, 17. Solution, 55, 57, 62, 63, 84, 86, 133, 134, 142. Sounder, 90, 92, 95, 96. Sounding board, 119. Source, charging, 83. South pole, 20, 21, 22, 25, 50, 54, 156. Spark gap, 102, 106. Spark jump, 99. Spring finger, 69. Square, 14, 17. Standard, 62, 63. Station, 94, 95, 117, 122. Steel, 18, 19. Steel magnet, 53. Sterilized, 12. Stirrup, 75. Stock bit, 13. Stock contact, 121. Storage, 82. Storage battery, 107. Storing, 82. Substances, 135. Sulphate, 55, 128, 133. Sulphur, 19. Sulphuric acid, 31, 84. Sulphuric acid voltameter, 55, 57. Superstition, 171, 173. Surging, 153, 154. Swinging magnet, 53. Swinging switch blade, 67. Switch blades, 66. Switches, 65, 66, 70, 77, 78, 90, 117. Switches, bar, 65, 68, 90, 91. Switches, bar, parallel, 67. Switches, heart-shaped, 78. Switches, piece, 77. Switches, reversing, 67. Switches, sliding, 67, 80. Switches, terminal, 8. Switches, two-pole, 65. System, circuiting, 79. T Tail-piece, 16. Tantalum, 169. Telegraph, 11, 90, 96. Telegraph key, 106. Telegraph sounder, 108, 109. Telegraphing, 94. Telephone, 12, 110, 113, 117, 118, 119, 120. Telephone circuit, 118. Telephone connections, 116. Telephone hook, 122. Temperature, 56, 88, 134, 161, 170. Tension, high, 38, 102, 184. Tension, low, 38, 98, 102, 179. Terminal, 31, 34, 35, 40, 48, 82, 86, 93, 95, 107, 116, 121, 122, 151, 152, 153, 154, 156. Terminal knob, 31. Terminal, secondary, 102. Terminal switch, 81. Theoretical, 160. Therapeutics, 187. Thermo-electric couples, 146. Thermo-electricity, 135. Thermometer, 56. Thorium, 169, 186. Thunderbolt, 171, 173. Tin, 136. Tinfoil, 31, 101. Tools, 11, 13, 17. Torch, brazing, 17. Transformer, 145, 146, 158, 159, 180, 182. Transformer, step-down, 182. Transmission, 38, 187. Transmit, 63, 95, 157. Transmitter, 12, 120, 121, 122, 123. Transverse, 16, 52. Transversely, 43. Trigger, 75. Tripod, 31. Tubular, 44, 45. Two-pole switch, 65. U Ultra-violet, 185. Uranium, 186. V Vacuum, 184. Vapor lamps, 169. Velocity, 60, 73. Vertical armature, 75. Vibration, 110, 111, 113. Vibratory, 110. Vise, 13. Voltage, 37, 38, 60, 61, 62, 63, 87, 88, 99, 147, 154, 165, 180, 182. Voltage, high, 158. Voltaic, 29, 32. Voltaic pile, 33. Voltameter, 7, 58, 88. Voltameter, sulphuric, acid, 55, 57. Volts, 60, 62, 87, 89, 132, 158, 159. W Water, 123, 138, 144. Water power, 142. Watts, 60, 61, 160. Wave lengths, 104, 110. Weight, 49. Welding, 13, 182. Winding, 18, 40, 47, 58, 159, 196. Winding reel, 14. Window connection, 76. Window frame, 78. Wire, 6, 18, 21, 26, 28, 156. Wire, circuiting, 79. Wire coil, 40. Wire lead, 70. Wire, parallel, 28, 49. Wireless, 12. Wireless telegraphy, 103, 104, 184. Wiring, 80. Wiring, window, 77. Workshop, 11, 17. Wound, compound, 48. Wound-series, 47. Wound-shunt, 47. X X-ray, 184, 185, 187, 188. Z Zinc, 17, 34, 35, 85, 135. Zinc plates, 33. THE "HOW-TO-DO-IT" BOOKS CARPENTRY FOR BOYS A book which treats, in a most practical and fascinating manner allsubjects pertaining to the "King of Trades"; showing the care and use oftools; drawing; designing, and the laying out of work; the principlesinvolved in the building of various kinds of structures, and therudiments of architecture. It contains over two hundred and fiftyillustrations made especially for this work, and includes also acomplete glossary of the technical terms used in the art. The mostcomprehensive volume on this subject ever published for boys. ELECTRICITY FOR BOYS The author has adopted the unique plan of setting forth the fundamentalprinciples in each phase of the science, and practically applying thework in the successive stages. It shows how the knowledge has beendeveloped, and the reasons for the various phenomena, without usingtechnical words so as to bring it within the compass of every boy. Ithas a complete glossary of terms, and is illustrated with two hundredoriginal drawings. PRACTICAL MECHANICS FOR BOYS This book takes the beginner through a comprehensive series of practicalshop work, in which the uses of tools, and the structure and handling ofshop machinery are set forth; how they are utilized to perform the work, and the manner in which all dimensional work is carried out. Everysubject is illustrated, and model building explained. It contains aglossary which comprises a new system of cross references, a featurethat will prove a welcome departure in explaining subjects. Fullyillustrated. _Price 60 cents per volume_ THE NEW YORK BOOK COMPANY147 FOURTH AVENUE NEW YORK +-----------------------------------------------------------------+ | Transcriber's Note. | | | | Every effort has been made to replicate this text as faithfully | | as possible, including obsolete and variant spellings and other | | inconsistencies. | | | | Minor punctuation and printing errors have been corrected. | | | | The first page of the original book is an advertisement. The | | page was moved to the end of the text. | | | | Some hyphenation inconsistencies in the text were retained: | | 16-candle-power and 16-candlepower, | | Electromotive and electro-motive, | | Electro-meter and Electrometer, | | Horseshoe and horse-shoe, | | Switchboard and switch-board, | | | | Two occurrences of 'Colorimeter' for 'Calorimeter' repaired. | +-----------------------------------------------------------------+