HISTORY, &c., OF INDUCTION INSTRUMENTS. 



287 



that it is not more difficult to understand than other forms of 

 apparatus. 



Part the Fifth. 



HISTOEIOAL AND CRITICAL ACCOUNT OF INDUCTION 

 INSTRUMENTS. 



In order better to appreciate 4he value of my induction instru- 

 ments, the description and properties of which have been set forth 

 in the preceding Parts, and to judge of the progress of the art of 

 fabricating electro -medical instruments, and also in order that the 

 physician may exercise an enlightened choice among these instru- 

 ments, I proceed, in the following pages, to pass in review the 

 principal forms of induction apparatus, from their origin to the 

 present day. I shall reprint the figures and description of two 

 learned physicists, and especially of one of them, who, in a work 

 I have had occasion to quote,^ has profoundly studied electro- 

 medical instruments. In the second place, I shall enter upon 

 certain critical considerations, that I have already in great part 

 set forth in 1855, upon the electro-medical instruments then in 

 use, and I shall point out their improvements, as well as the 

 desiderata which still remain to be attained. 



§ I.— Historical Eeview. 



1 . — Magneto- eledriG instruments. 



A. — Faraday's instrument. — "The first magneto-electric machine," 

 says M. de la Rive, was constructed by Faraday (fig. 67). It 

 consists of a copper 

 disc, c, movable in a 

 vertical plane upon a 

 horizontal axis, and 

 which is made to turn 

 between the two 02:)po- 

 site poles of a magnet, 

 n. We have seen that 

 if we connect the two 

 ends of the galvano- 

 meter g, the one, w, 

 with the axis of the 



. , Fig. 67. — Faraday's instrument. 



disc, the other, w, 



with a point on its circumference, the deviation of the needle 



which takes place in one or the other direction, according to 



^ F. P. Le Roux, loc. cit. 



