CAUSES AND PHENOMENA OF MOTION. 31 



after stimulation of the muscle by a single induction-shock: the middle 

 line (/) is that described by the marking-lever, and indicates by a sudden 

 drop the 'exact instant at which the induction-shock was given. The 



pendulum swings along the arc to D on the left of figure, and is caught by its spring. 



lower wavy line (t) is traced by a vibrating tuning-fork, and serves to 

 measure precisely the intervals of time occupied in each part of the con- 

 traction. 



FIG. 283. Tracing of a double muscle-curve. To be read from left to right. While the muscle 

 was engaged in the first contraction (whose complete course, had nothing intervened, is indicated by 

 the dotted line), a second induction -shock was thrown in, at such a time that the second contraction 

 began just as the first was beginning to decline. The second curve is seen to start from the first, as 

 does the first from the base line. (M. Foster.) 



It will be observed that after the stimulus has been applied, as indi- 

 cated by the vertical line s, there is an interval before the contraction 



