THE STUDY OP MUSCLE PHYSIOLOGY. 



177 



wise prepared to receive impressions made upon it by a jHjint 

 and capable of being raised or lowered, and its movements reg- 



Fig. 161.— Myographic tracing, such as is obtained wlien the cylinder on which it is 

 written does not revolve during the contraction of the muscle (after McKendrlck). 



ulated. The cylinder is ruled vertically into a certain number 

 of spaces, so that, if its rate of revolution is known and is con- 

 stant (very important), the length of time of any event recorded 

 on the sensitive surface may be accurately known. This whole 

 apparatus may be considered a chronograph in a rough form. 



But a tuning-fork is the most reliable form of chronograph, 

 provided it can be kept in constant action so long as required ; 



Fig. 162.— Marey's chronograph as applied to revolving cylinder (after McKendrlck). 

 a, galvanic element; b, wooden stand bearing tuning-fork (two hundred vibrations 

 per second); c, electro-magnet between limos of tuning-fork; (!,€, positions for 

 tuning-forks of one hundred and fifty vibrations per second; /, tuning-fork lying 

 loose, which may be applied to d; g, revolving cylinder; h, electric chronograpn 

 kept in vibration synchronous with the tuning-fork interrupter. The current 

 working the electro-magnet from a, is interrupted at i. Foucault's r^ulator is 

 seen over the clock-work of the cylinder, a little to the right of g. 



12 



