LARGE DOUBLE-CURRENT VOLTA-FARADIC APPARATUS. 259 



conditions of exactitude necessary to formulate the physiological 

 and therapeutic applications of electricity. 



F. — Pedal Bheotoyne and TremUer. 



As I have shown at the commencement of the chapter, the 

 intermittences during faradization should be few or frequent, slow 

 or quick, according to the physiological or therapeutical indication 

 that is to be fulfilled. Any apparatus that does not provide for 

 this requirement is incomplete, and may even be dangerous. In 

 order to meet all wants, I have adapted to my instruments two 

 varieties of rheotome, — the pedal and the trembler. I have also 

 described already (page 123, fig. 40) a rheotome that I have 

 contrived in order to avoid the alternations of an induced current, 

 and to render it either centripetal or centrifugal. 



(a). Pedal. With the pedal (Y, fig. 52) the operator obtains, at 

 pleasure, intermissions of greater or less rapidity. 



For this purpose, I was for a long time in the habit of employing 

 a toothed wheel attached to the instrument (D, fig. 51), but to 

 turn this wheel occupied the hand which should be reserved 

 to control the graduator, the moderator, the commutators of the 

 coils and poles, &c. For this reason, I have long abandoned 

 the wheel in favour of the pedal ; more especially as the former 

 complicated the apparatus, and sometimes became a cause of its 

 deterioration. 



I attach little value, as a rule, to any system of intermittence 

 that cannot be regulated in accordance with the requirements of 

 experimentation or of treatment. I have made several small 

 mechanical rheotomes, in which the motor power was furnished by- 

 clock-work, which would maintain more or less rapid intermissions 

 for a considerable time. Experience soon taught me that such 

 movements could not replace those that were subject to the will of 

 the operator. Notwithstanding the convenience of the mechanical 

 rheotomes, I returned to the toothed wheel, and eventually to the 

 pedal. 



On occasions where great precision was required, I have, how- 

 ever, employed a clock to which a i-heotome was adapted, so as to 

 give exactly, at pleasure, one, two, three, or four intermissions per 

 sec(md.^ 



(&). Trembler. — However rapid we may be able to render the 

 intermissions by means of the toothed wheel or the pedal, they yet 

 never reach the speed given by the trembler, — a speed such that 



' This rheotome, fitted to an electric j rupting the circuit by a common metro- 

 clock, was made by M. A. Mathieu. The nonie. 

 same effect has been produced by inter- j 



■s 2 



