Electricity. 103 



by a winch or handle, as represented in the plate. 

 The axis of the other cap is inserted in the sup- 

 porter E; O is the glass pillar to which the 

 cushion is fixed. At the bottom of the pillar O 

 is a brass screw T, which brings the cushion at 

 the top of the pillar nearer to the cylinder or re- 

 moves it further, at the discretion of the ope- 

 rator, when he wishes to increase or lessen the 

 pressure. 



Y Z is the prime conductor, which by means 

 of metallic points takes the electric matter imme- 

 diately from the cylinder ; and in order that the 

 electric fluid may be accumulated upon the con- 

 ductor, and not run off to the earth, the con- 

 ductor is insulated, that is, placed upon a non- 

 conducting body, which will not attract the fluid 

 away from the conductor. ' The insulating sub- 

 stance, in this case, is a glass pillar, L M (glass 

 being the most convenient substance for this 

 purpose), and VX is the wooden foot or base of 

 the glass pillar. The conductor is always of 

 metal, at least externally, as metals are found to 

 be the most powerful ,of the conducting bodies. 

 They are commonly made of wood, and cased 

 over with tin-foil. 



When electrical machines were first constructed, 

 instead of a cylinder, a glass globe was made use 

 of; and when this was turned, the hand of the 

 operator was applied to it, and afterwards a piece 

 of glove leather ; but the most effectual and easy 

 means is now found to be a leather cushion, 



