138 THE ROYAL SOCIETY OF CANADA 
Hence it is easy to understand that the variation of speed during the 
first twenty minutes after a winding was practically negligible. Before 
each observation during a set of readings the spring was tightly 
wound, thus assuring a uniform speed. To obtain various speeds 
weights were suspended from the driving shaft of one of the lighter 
wheels. For instance, with no weight on at all, the fastest speed was 
-124 revolutions per second. 
With 20grms. -115 revolutions per second 
= 30 “ iq? « 
40 « -108 « « « 
5 0 « 5 1 05 7 “ “ “ 
60 « -102 « « « 
70 « L 1 00 “ “ “ 
80 « f 09 7h « « « 
00 “ .094 « “ « 
1 00 « 2 092 6 “ « « 
1:16)" * -087 « « « 
The observations were repeated many times to be certain that 
in each case the number of revolutions per sec. did not vary. 
RESULTS. 
The needle and the disc were cleaned with fine emery paper and 
then rubbed with chamois. The spring was wound tight, and just 
enough pressure exerted to cause good contact when stationary. 
The disc was then allowed to revolve at the rate of -124 revolutions 
per sec., the resistance at once increased from 0 to ©. The speed 
was then decreased and the resistance fell slightly. By making the 
speed less and less the resistance showed corresponding decreases. 
The slowest rate obtainable with the apparatus was -087 revolutions 
per sec. The resistance was then 500 ohms. In this way it was no- 
ticed that the resistance was proportional to the number of revolutions 
per sec., the pressure being kept constant. Curve I Fig. 2 shows 
the relation between the speed of rotation and the resistance for the 
smallest pressure as already indicated. 
