114 APPENDIX I. 



theoretically be ascertained with any degree of pre- 

 cision. But, if required, this could easily be done 

 experimentally, by recurring to Dr. Thomas Young's 

 original plan*, viz., by causing a tuning-fork to 

 record its vibrations upon the plate, together with 

 the curve traced by the contraction of the muscle. 

 On the present occasion this would be useless, as it 

 is only intended to show that there is a larger 

 interval between the instant of stimulation and the 

 beginning of contraction, if a part of the nerve 

 farther from, than if a part of it nearer to, the 

 muscle be acted upon. For this purpose it is only 

 requisite that the motion of the plate should always 

 follow the same law and attain the same velocity, 

 and that the point of the datum-line, corresponding 

 to the instant of stimulation, should always be the 

 same. 



In the spring-myographion the latter condition is 

 fulfilled in the same manner as in Professor Helm- 

 holtz's, and every other myographion. The frame 

 carrying the plate has a projecting piece or tooth, 

 which, just when the frame has reached its highest 

 speed, strikes a lever, and thus breaks the primary 

 circuit of the induction apparatus. This, of course, 

 always happens in exactly the same position of the 

 plate, whatever may be its velocity ; so that in 

 order to find the point of the datum-line correspond- 

 ing to the instant of stimulation, it is only necessary 

 to move the plate with the hand along its guides so 

 slowly that the contraction of the muscle, instead of 



* A Course of Lectures on Natural Philosophy and the 

 Mechanical Arts. London, 1807. Vol. i., p. 190. 



