THE GRAPHIC METHOD 91 



the writing point returns in the same line. When 

 the drum revolves, the writing point describes a 

 curve as the muscle contracts. The maximum 

 shortening of the muscle, or height to which the 

 load is lifted, is measured by a perpendicular 

 drawn from the highest point of the curve to the 

 abscissa. The time required for the muscle to 

 reach this height, however, is not the distance on 

 the abscissa from the beginning of the curve to 

 the perpendicular, but to the point at which the 

 segment of a circle of a radius equal to the 

 length of the lever would cut the abscissa when 

 drawn from the highest point of the curve. Prac- 

 tically, this measurement is made by turning the 

 drum back until the point of the raised lever 

 rests at the summit of the curve, and then, 

 while the drum is at rest, allowing the lever 

 to write the ordinate by falling down to the 

 abscissa. 



Perpendicular ordinates may be secured by a 

 long pin passed transversely through the end of 

 the writing lever, and bent twice at right angles, 

 first parallel to the paper and then towards it. 

 The lever is perpendicular to the paper and very 

 near it; the weight of the pin keeps the point 

 against the paper as the lever rises. The perpen- 

 dicular writing has many faults in common with 

 arc writing. 



