THE GRAPHIC METHOD 89 



ning its movement (inertia of position). Once 

 in motion, the weight tends to keep moving, 

 and thus to continue the record of contraction 

 after the actual contraction has ceased (inertia 

 of motion). As the inertia of motion increases 

 with the mass and the square of the velocity, 

 the lighter the lever the less the error. The 

 disposition of the weight relative to the axis 

 is also of importance. In a swinging system, 

 the nearer the mass to the axis of rotation, the 

 less are the after vibrations or pendulum-like 

 oscillations which continue after the original im- 

 pulse has ceased. For this reason, in experi- 

 ments likely to be disturbed by after vibrations, 

 the weight which the muscle lifts is attached 

 to the small pulley, so as to be as near the 

 axis as possible. In this case, the weight on 

 the muscle is of course not the weight hung on 

 the pulley; the pulley weight must be divided 

 by the number of times the radius of the pulley 

 is contained in the distance between the axis 

 and the point of attachment of the muscle to the 

 lever. 



It will be observed that the writing point is a 

 strip of tinsel bent slightly and placed parallel 

 to the writing surface. It is very easily moved 

 in a direction at right angles to the writing sur- 

 face, but resists movement in a vertical direction. 



