122 



PHYSIOLOGICAL PHYSICS. 



[Chap. XI. 



63. The element K is connected with the long com- 

 pensator at a and b. From a and c (c is the slider) 

 wires go to the commutator c, the cross being in, and 

 from the end cups of c wires proceed, one to the bous- 

 sole B, the other to the troughs T, and from them to B, 

 a key (not represented in the figure) being interposed. 



a 



Fig. 63. Compensation of Muscle Current. 



To perform the experiment? push c close up 

 to a, and be sure that it makes contact with it, so 

 that no current from K at present gets access to B. 

 The muscle current, however, can pass round B. 

 Note the direction of the needle's deflection when the 

 muscle is so placed as to touch, say, the right-hand 

 trough with the transverse section. Then remove the 

 muscle, and connect the troughs by the closing cushion. 

 The needle being again at zero, slowly remove the 

 slider from a ; a portion of the current from the 

 Daniell will get to B, and will deflect the needle. Note 

 how the position of the commutator is related to the 

 direction of deflection. Now push c again into con- 

 tact with a, replace the muscle ; open the key, and get 

 the deflection due to the muscle current. Lay the 



