582 Prof. F. T. Trouton and Mr. S. Russ on the Rate of 



unduly irregular. After many trials made with this appa- 

 ratus it was decided, for the above reasons, to move the 

 shutter mechanically. The best of the tracings obtained by 

 the previous experiments was utilized for constructing a cam 

 for this purpose. The cam, which was cut out of wood, was 

 made to close the shutter by a uniform rotation about its 

 axis. Fig. 2 illustrates the way in which this was done. 



Fiir. 2. 



H is a small brass wdieel fixed to a brass strip which passes 

 underneath the cam T and is joined to the shutter M ; a cord 

 fixed to the other end of the shutter passes over a pulley R 

 and carries a weight W w T hich keeps the wheel H tightly 

 pressed against the cam. As the cam rotates H is pulled 

 forward and the shutter moves in at a varying speed. 



The uniform rotation of the cam was obtained by means of 

 the toothed wheel L, which engaged in an endless worm N 

 cut in a steel shaft, the other end of which carried a pulley- 

 wheel V which was driven by a small motor highly geared 

 down. The portion FGr on the cam entails no forward motion 

 of H, and is to allow the speed of the motor to become constant 

 after starting. The method of carrying out an experiment 

 was as follows : — 



The condenser was charged for 1J minutes to 20 volts, 

 discharged through the key B, and the coatings then con- 

 nected to the quadrants and the parallel plates P, Q. The 



