154 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Fig. 3. 



magnet towards the left. If the magnet is pulled out a certain 

 distance toward the right, the pendulum bob is brought against the 

 stop f, and any further motion of the magnet detaches the pendulum ; 

 the magnet is at once released by the observer, and falls back to a point 

 fixed by the stop e, so as to arrest the pendulum at the completion of 

 its first swing. The pendulum rod is screwed into the edge of an eb- 

 onite disk. ^, three eighths of an inch thick and one inch in diameter, 

 through the centre of which passes the pin h^ which forms the axis 

 of suspension. Attached to the disk g are two copper strips, y, of 

 which one is shown in the figure, and which, as the pendulum swings, 

 rub lightly upon the edge of the fixed disk k. Inserted in the latter 

 are four pieces of copper m, n. In the ordinary position of the 

 pendulum as shown in the figure, the copper strips j j, which are 

 connected with the condenser by the binding screws at p, rest upon 

 the opposite copper pieces m m, and through them are in circuit with 

 the binding screws at q, which are connected with the galvanometer. 

 The condenser is thus short circuited through the latter. 



When the pendulum swings, the strips jj make contact at the lowest 

 point of the swing with n n, which are connected through the binding 

 screws at r with the battery ; and this connection is maintained until 

 the pendulum reaches its lowest point on the return swing, when the 

 strips y y pass to the copper pieces, and the condenser is discharged 



