A system of electrotherapeutics as taught by the International correspondence schools, Scranton, Pa.

  • International Correspondence Schools.
Date:
1899-1902
Catalogue details

Licence: Public Domain Mark

Credit: A system of electrotherapeutics as taught by the International correspondence schools, Scranton, Pa. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    the storage-battery has been given in Art. 30, The Physics of Roentgen Rays. 23. Lighting Circuit.—The minimum of attention is required on the part of the operator when the incandescent- lighting circuit is utilized. All that is required under this arrangement is simply to close a switch and the current is flow- ing. Ordinarily there are two kinds of currents available, the direct and the alternating. The most universally useful of the two is the direct current, because the alternating cannot be used in cataphoresis, electrolytic, and galvanic treatments. For cau- tery and lamps it is immaterial which current is used. It would seem natural to suppose that a 110-volt lighting current could be used directly for cautery purposes, and that by inserting a resistance-coil or a number of incandescent lamps of suitable resistance in parallel, any current-strength could be obtained. But this method has certain drawbacks that make it objectionable. A cautery has a very low resistance, and, to send a current of the required strength through it, demands a comparatively low pressure. For instance, let the united resistance of the cautery and conductors be .1 ohm; then, with p 110 a pressure of 110 volts the amperage would be C = -l5 = —=- = K . 1 1,100 amperes. As the required amperage rarely goes beyond 25, and usually is much below this, it is clear that a large resistance must be inserted in the circuit to bring the pressure within reasonable limits. Suppose that we desire a current of 5 amperes for a cautery of .035 ohm's'resistance. It is then necessary to insert a resist- ance in the circuit, in series with the cautery, sufficiently large to make the joint resistance of the cautery and conductors equal W 110 to 22 ohms, as found by Ohm's law, viz.: R = -= = —=- = 22. V 5 Let the united resistance of the cautery and the conductors be . 1 ohm, then the resistance of the rheostat would be 22 — .1 = 21.9 ohms. The reduction of pressure that takes place in this resistance isi?=CX.R=5x21.9 = 109.5 volts, and the num- ber of watts lost is W= E X G = 109.5 X 5 = 547.5 watts, a