THE DYNAMOMETER-CHRONOGRAPH. 



79 



of these weights at a lever-arm of 5 centimeters (the effective radius of the pulley) 

 is balanced by the tension of the clock-si:)ring and is measured by the longitudinal 

 motion of the pencil P". On account of the appreciable friction of the guide- 

 wheel in the helical groove, two measures are desirable for exact calibration in 

 each case at an upper and lower limit of repose. The mean of these is taken as 

 the true extension for the given weight, and the observation is repeated three 

 times with each weight to eliminate errors of observation. This series of observa- 

 tions was made with the set-screw in the "0" hole, the 5th hole, and the 10th 

 hole, in order to get a sufficiently wide range of action for the instrument. 



The following table, XVI, gives the system of calibration obtained from 

 experiments made November 14, 1890 — F. W. Very, observer : 



Table XVI. 



Calibration of Clock-Spring of Di/tiamomcter. 



Weight applied at circumference of large pulley, effective radius 5 

 centimeters, by cord passing over a small pulley at edge of table. 



