PLATE ELECTRIC MACHINE. 



209 



rubber, a negative and a prime conductor. The electric is a glass 

 plate, one, two or three feet in diameter. This plate has an axis 

 and handle, and is supported upon two upright columns. The rub- 



FIG. 146. 



ber is made of two cushions of silk or leather, covered with amal- 

 gam. They press upon the sides of the plate and are supported 

 from the negative conductor, with which they are in electric con- 

 nection. The negative conductor, JV, is supported upon an insulat- 

 ing column and placed in electrical connection with the earth by 

 means of a chain or wire, not shown in the figure. The prime 

 conductor, C, is supported upon an insulating column. One end of 

 the prime conductor terminates in two arms, which extend one on 

 either side of the plate. These arms being studded with points 

 projecting toward the plate are called combs. The teeth of the 

 combs are not shown in the figure ; they do not quite touch the plate, 

 A silk bag is often supported so as to enclose the lower part of the 

 plate. All parts of the instrument except the teeth of the combs 

 are carefully rounded and polished, sharp points and edges being 

 avoided. 



346. Operation of the Plate Machine. The 



plate is turned by the handle. The neutral fluid is de- 

 composed by the friction of the rubbers. The -f of the 



