108 PROCEEDINGS OF THE ACADEMY OF [1888^ 



shuntiug off from the circuit of a standard element, a Dauiell's cell 

 for example,\vhose electro-motive force is kno\vn= 1 -08 Volt, an amount 

 of current sufficient to neutralize or compensate the current deflect- 

 ing the magnet, the latter due to the electro-motive force of the- 

 muscle or nerve and which is to be determined. Thus, for example, 

 let us suppose that the electrical current diverted by the non-polari- 

 zable cylinders or electrodes, Fig. 1 (E) from the nerve or muscle (]\I)- 

 to the galvanometer (G) be sufficient to deflect the magnet to an 

 extent corresjjonding to 267 divisions of the scale. If now the 

 compensator be moved so that the wheel III be opposite (n) 

 for example, part of the current from the Daniell element will return 

 through IVII F whence it came and part through III P" to the 

 muscle (M) and, being in the reverse direction to that of the current 

 from and due to the muscle, the magnet will be slowly brought back 

 from the the 267th division of the scale to zero, the wheel III then 

 standing at (n), or the 820th division of the wire of the compensa- 

 tor, the latter (N) being divided into 1000 parts. Such being the 

 case it is evident that the electro-motive force of the muscle or X is to 

 that compensating it, or to (1), (the amount of the compensating 

 force depending upon the resistance oflfered by the fractional j^or- 

 tion of the wire L) as the electro-motive force of the Daniell element 

 or (E) is to the whole resistance or W-fL, or more briefly: — 



X : 1 : : E : W+L 

 or 



In as much, however, as the fractional portion of the wire (1) is to 

 the number of its divisions or (n) as the whole wire (L) is to the 

 number of its divisions X we shall have 



1 : n : : L : X 



1 



or 

 nL 



X 



If now this value of 1 be substituted in equation (1) we shall 

 obtain 



"^ - X (1 + W) X E (2) 

 L 

 and it only remains, n and X being known, to determine the ratio of 

 W to L to obtain the value of X or the electro-motive force of the 



