HISTORY, &c,, OF INDUCTION INSTRUMENTS. 



295 



made easily portable, and adapted for use in practical medicine 

 (fig. 76). 



"The ineans of graduation are the same as in Page's instrument. 



" MM. Breton, following the example of M. Duchenne, wound 

 two coils of wire round the branches of their permanent magnet;^ 

 the external is formed by a finer and longer wire than the internal, 

 and they can, at pleasure, utilize the induced currents that are 

 developed in one or other of these coils, in the effects of which they 

 can discover certain differences. We shall examine this question 

 more fully, with reference to the instrument of M. Duchenne." ^ 



H. — Gaijfes instrument. — " This is at once the instrument of 

 Saxton and of Pago ; or it may be described as Page's instrument, 



Fig. 77.— Gaiffe's instrument. 



in which the bar of soft iron has been replaced by Clarke's electro- 

 magnet (fig. 77). 



" The chief merit of the maker of this instrument has been to 

 understand that, as magnets have a force relatively greater in 

 proportion as their weight is less, while the induced forces rapidly 

 increase as the distances diminish, there was every advantage in 

 reducing the size of the apparatus, when tension, rather than 

 quantity, is desired. 



" Thus, the magnet of the instrument, represented above, weighs 

 only half a kilogramme, and will support about five kilogrammes. 



' Le Roiix, p. 31. and weaker than the present one. The 



^ This arragement of the magneto- former is that which is generally to be 



electric apparatus of the MM. Breton found in the Paris hospitals, although 



is quite recent. Their original instru- ; the latter is much to be preferred on 



ment had only one coil ; and it is smaller account of the recent improvement. 



