. The medical and surgical uses of electricity. . Fig. 6q.—Cabinet Battery with High-Tension Coil and Wire Rheostat CVan Houten & Ten Broeck). APPARATUS FOR ELECTRO-THERAPEUTICS. 285 means of two extra brushes the current from the machine is commutatedinto a direct, or rather an interrupted, galvanic current, which is inter-rupted into the patients circuit by means of a switch by which the oper-ator may at will change the current from alternating to direct. Rheostats.—The general object and principle of the rheostat has beenalready described. It remains here to speak of those forms that are be
. The medical and surgical uses of electricity. . Fig. 6q.—Cabinet Battery with High-Tension Coil and Wire Rheostat CVan Houten & Ten Broeck). APPARATUS FOR ELECTRO-THERAPEUTICS. 285 means of two extra brushes the current from the machine is commutatedinto a direct, or rather an interrupted, galvanic current, which is inter-rupted into the patients circuit by means of a switch by which the oper-ator may at will change the current from alternating to direct. Rheostats.—The general object and principle of the rheostat has beenalready described. It remains here to speak of those forms that are bestadapted for electro-therapeutics. A form of rheostat very well known to electro-physiologists and elec-tro-therapeutists is that of Siemens, and introduced into electro-therapeu-tics by Brenner in his researches on the ear. The unit of Siemens is a. Fig. 70.—Galvanic and Faradic Adapter (Kennellys). (For use on no or 120 volt circuit.) column of mercury, one metre long, with a transverse section of one squaremillimetre, at 32° F. Hydro-Rheostat or Carbon-Rheostat.—^For all the practical purposes ofelectro-therapeutics, even for the most delicate applications to the most;delicate organs, as the ear, eye, etc., the common water rheostat or thecarbon rheostat are sufficiently precise, and in convenience are incompar-ably superior to the stopper rheostats. But for the measurement ofthe resistance in ohms the more modern instruments are constructed ofGerman silver wire for the reason that its resistance is affected but:slightly by changes of temperature. Wire stopper rheostats, however— 286 ELECTRO-THERAPEUTICS. although useful in enabling the physician at once to inform himselfof the varying degrees of resistance in ohms of the human body—arefor general purposes of utility of no more value than the simpler formsto be describ
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