Strain along the Lines of Force. 685 



diameter than the mould, was fastened to it by screws. The 

 ends o£ the moulds were closed by brass screw-caps. After 



Fis:. 1. 



the casting was made, the caps and holding screws were 

 removed, and the perfect casting slipped out of the mould by 

 heating it quickly. The large brass plate at the bottom was 

 removed by heating it gently, and the bottom electrode, thus 

 exposed, was fastened to the base plate of the frame of the 

 apparatus, fig. 2. Then the brass tooth was replaced by the 

 one of ebonite. During this operation the top brass plate 

 was slipped off, this being done so that the upper plate of the 

 frame might replace it as an electrode. 



When the casting was out of the mould, the ends of the 

 three lugs on each plate were exposed, forming two sets of 

 three vertical lines each. Two of these lines of lugs of each 

 set were covered with insulating wax to prevent leakage, and 

 the lugs on the third line of each set were connected by wires 

 so that one set might be charged and the other grounded, 

 fig. 2. After the electrical connexion was made and tested, 

 these terminals were also covered with the insulating wax. 

 We thus have sixteen plate-electrodes (counting the upper 

 plate of the frame as one), connected to the ground, of which 

 the top and bottom ones were fastened rigidly together, and 



