of the Weight of a Body on its state of Electrification. 357 



The balance itself is shewn in fig. 4. It is rigidly made so 

 that the applied electric forces shall not produce distortion. The 

 case, guard cylinder, field plates and beam are constructed of 

 magnalium. Referring to the figure, A A represents the beam 

 with its arresting arrangements aaa, B one of the end pieces, CG 

 the guard cylinder and DE the insulated field plates. The beam 

 is electrically connected to the guard cylinder by means of its 

 steel knife edge which bears on a grooved steel plate attached to 



Fig. 4. 



a pillar screwed to the guard cylinder. The object of the groove 

 in the bearing plate is to prevent side slipping of the knife edge 

 under the action of the electric forces. The guard cylinder itself 

 is rigidly fixed to the back of the case, and the whole earthed by 

 means of the earth wire shewn in fig. 3. (It should be noted that 

 all the earth connections are made with one wire as shewn in that 

 figure.) 



It will be seen from the figure that a small amount of play is 

 allowed between the piece B and the guard cylinder. This allows a 



