HISTORY, &c., OF INDUCTION INSTRUMENTS. 319 



necessary to have recourse to a strong induced current of powerful 

 tension. 



These facts show the insufficiency of the very small induction 

 instruments of Gaiffe, Kuhmkorff, and Trouve, — instruments the 

 extra currents of which are almost powerless, and of which the 

 induced currents have not sufficient tension to reach the muscles, 

 or to pass through any depth of tissue. (It is especially with slow 

 intermissions that we can appreciate the weakness of these small 

 instruments.) 



Instruments of very small size and of easy transport can 

 therefore only be utilised for therapeutical purposes in a very 

 small number of cases. I regard them as pretty toys, which may 

 be relegated to the domain of drawing-room physics. MM. Gaiffe, 

 Legendre and Morin, and Kuhmkorff, have fortunately constructed 

 instruments of medium force, almost equal to that of my own small 

 instrument in the form of a book (see figs. 58 and 60), and which 

 fulfil nearly all the requirements of practice. 



Tiiat of M. Gaiffe preserves the shape of the small instrument 

 represented in fig. 86. Its size being only increased one-fourth, 

 it is still very portable, and its flattened shape allows it to be 

 carried under the arm like a book. It is not the same with the 

 instruments of M. Kuhmkorff, or of Legendre and Morin, which 

 are contained in boxes that must be carried by the hand. The 

 instrument of Kuhmkorif is twice the size of that of Legendre and 

 Morin. It might be easily reduced by about a third, if the maker 

 would substitute graduation by a metallic tube for graduation by 

 the mutual influence of the coils. The former has, over the latter, 

 advantages which have induced me to give the preference to it 

 (see p. 253 ). The modification which I propose would simplify 

 the construction of Ruhmkorff's apparatus, and would conse- 

 quently diminish its size and its price. 



These instruments of medium power are far from attaining the 

 force of my large volta-faradic apparatus (see figs. 52 and 56), 

 which has rendered me such services in cases in which the former 

 would have been insufficient or powerless, and which, notwith- 

 standing its greater size and greater weight, is still portable. It 

 usually serves me for my own chamber apparatus, and it is worked 

 by a fraction of my sulphate of lead battery. 



I would advise manufacturers to take it as their model, 1. as 

 regards its power, which could not be exceeded, I believe, without 

 danger to patients ; 2. as regards its graduation by internal and 

 external metallic tubes ; and, lastly, as regards its commutator of 

 the coils, and of the poles. They should not forget to attach to it 

 a water moderator (F, fig. 52), which converts, at pleasure, this 



