PHYSICAL AND ELECTRICAL ENGINEERING LABOR TORY MANUALS VOL. III. ELECTROTECHNICS JOHN HENDERSON, HEAD OF THE PHYSICS AND ELECTRICAL DEPARTMENT, WITH DIAGRAMS. PREFACE TO THE SERIES. IN bringing before the public these laboratory manuals, it has been the object of the author to provide a course of instruction for carrying out a progressive series of experiments in Physics and Electrical Engineering, arranged so that the usual apparatus at the disposal of a laboratory, though not especially designed for any particular experiment, may nevertheless be used with advantage in a variety of ways. Able courses of instruction in experimental work have already appeared, and have done a vast amount of good but as these usually require expensive apparatus made and arranged for each experiment, they have not become so generally useful as otherwise might have been the case, especially in such instances where the scope of the work undertaken precludes all possibility of separate and special apparatus being provided for each independent experiment. In technical work this is more particularly the case, seeing that in actual practice set of instruments must be put to very divergent uses, in order that results may be obtained quickly and with sufficient accuracy for commercial work. This use of apparatus for ends not specially intended is io itself a training of considerable importance, to any student who will afterwards, in his daily life, have to so adapt for different purposes such instruments as may be available at the time. vi Preface to the Series It has not, however, been forgotten that most apparatus thus used is too often placed under circumstances inconsistent with accurate work, and to this end very careful instructions will be found in the more advanced volumes, for guarding against such disturbing influences as time, situation, temperature, and magnetic forces this being too often neglected in general laboratory and commercial work, it being frequently forgotten that a set of apparatus arranged for a particular test is some times not only a centre of disturbance itself, but is liable to disturbance from other apparatus in use in its neighbourhood. The precautions thus indicated are of especial importance in technical work, where the disturbing influences are of such a powerful nature, as may be found in engine-rooms and dynamo houses, where high and varying temperatures and leakage magnetic lines are very prevalent. Another way in which an alteration has been effected is to, as far as possible, arrange experiments where a student working alone. may be able to obtain satisfactory results. In a large proportion of the existing laboratory manuals, groups of students are expected to work together but a number of years of practical experience with students of all kinds has convinced the author, that habits of individual accuracy and self-reliance can only be acquired by separate and unaided work. Of course, in advanced work it is often necessary that two or more students should work together, in order that simultaneous observations should be taken but it is most desirable that students so combined should have had considerable individual training and experience. It is particularly desirable that every experiment should be repeated until a set of consistent results have been obtained. In this way only can experience and accuracy be acquired. This series is divided into two courses, to which Vol. I. is a general introduction... --This text refers to the Paperback edition.