Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: Fig. 27 is an illustration of a very fine galvanoscope. It may be readily attached to any battery ; and if a current is running, the needle will be deflected in the direction of the current. If the needle turns to the left, we know the negative pole is on that side; if to the right, then we know the negative pole is to the right. Fig. 27. The number of degrees of deflection shown by the needle indicates the strength of the current. In this way, we can know exactly what we are doing; know the direction of the current, its strength, etc. ; and this is very important in many cases of gal- vano-therapeutics. Other varieties of galvanoscopes are made, and in use, but this is a good one, and easily managed by anybody who can operate a battery. To use it, we simply attach the conducting cords of the battery to the posts of the galvanoscope and the electric current is closed. chapter{Section 4Rheotomes.—A rheotome is a contrivance for interrupting the electric current. Without something of this kind we could not have an induced current, for this is only present in the secondary coil, at the opening and closing of the primary current. By means of the rheotome, the primary current is broken and closed rapidly, so that the induced cm-rent seems almost like a continuous one. We also use the rheotome on galvanic batteries. By interrupting the galvanic current, we can frequently excite muscular contraction more perfectly and powerfully than can be done by applying the faradic current. But the interrupted galvanic current is not like the induced faradic current—a to-and-fro current— but a succession of straightforward currents. Fig. 28 is an illustration of Powell's rheotome. These in- Fig. 28. struments—any of them in the market—may be attached to any battery; and some galvani...