of the Weight of a Body on its state of Electrification. 359 



with the exception of a small space for observing the mirror K 

 which has been closed in with a grid of fine wire. The results, 

 however, are exactly the same whether the windows are covered 

 or left bare. The whole apparatus is enclosed in a box of wood 

 2 inches thick and provided with double windows of plate glass. 



The diagram is approximately to scale. The diameter of guard 

 cylinder is 14-3 cms., distance between this and field plates 3 mms., 

 the end pieces B, which are square with rounded corners, 4'9 cms. 

 square. Weight of end pieces about 28grms. each, total weight 

 of beam about 260 grms. 



u S 



Fig. 5 is a diagram of the keys K and L of fig. 8. Z is a 

 paraffin block with mercury cups and connections as shewn. The 

 cups A, B are connected to the negative and positive terminals of 

 the top tray of cells and C, D to the negative and positive terminals 

 of the bottom tray. E and H are connected to two other cups Q, 

 R, which are permanently connected to the electroscopes and to 

 the key J in fig. 3 by wires 8, T. The wires U, V to the balance 

 can be dipped into the cups Q, R by means of the lever W to 



