44 



ELEMENTARY LESSONS ON [CHAP. i. 



The action of the machine is, in all points of theoretical 

 interest, the same as that of the cylinder machine. Its 

 advantages are that a large glass plate is more easy to 

 construct than a large glass cylinder of perfect form, and 

 that the length along the surface of the glass between the 

 collecting row of points and the edge of the rubber 



cushions is greater 

 in the plate than in 

 the cylinder for the 

 same amount of sur- 

 face exposed to fric- 

 tion ; for, be it re- 

 marked, when the 

 two electricities thus 

 separated have col- 

 lected to a certain 

 extent, a discharge 

 will take place along 

 this surface, the 

 length of which limits 

 therefore the power 

 of the machine. In 

 a more modern form, 

 due to Le Roy, and modified by Winter, there is but one 

 rubber and flap, occupying a little over a quadrant of the 

 plate, and one collector or double row of points. In 

 Winter's machine the prime conductor consists of a ring- 

 shaped body, for which the advantage is claimed of 

 collecting larger quantities of electricity than the more 

 usual sausage - shaped conductor. Whatever advantage 

 the form may have is probably due to the curvature of 

 its surface being on the whole greater than that of the 

 commoner form. 



41. Electrical Amalgam. Canton, finding glass 

 to be highly electrified when dipped into dry mercury, 

 suggested the employment of an amalgam of tin with 

 mercury as a suitable substance wherewith to cover the 



