102 



ELEMENTS OF STATIC ELECTRICITY. 



The jar should be made self-discharging, by bringing 

 the knob of a conductor, connected with its outer 

 coating, within sparking distance of the knob of the 

 jar. 



Lane's unit jar, shown in Fig. 30, is constructed on 

 this principle. 



A bent brass rod is connected by a band to the outer 

 coating; its upper end terminating in a ball through 

 which passes a horizontal sliding rod, terminating in a 

 ball at its inner extremity; and having an ebonite 

 handle at its outer extremity, by which the ball can 



be adjusted to any required 

 distance from the knob of the 

 jar. 



To estimate the comparative 

 energy of different machines, 

 a uniform rotation of the plates 

 must be maintained by a given 

 number of revolutions per min- 

 ute ; and the number of dis- 

 charges in a given time of the 

 unit jar, connected with the 

 prime conductor, will then be approximately correct 

 for the energy of each. 



THE ELECTRIC CHIME. This instrument is used in 

 connection with the machine, to illustrate electric 

 attraction and repulsion. 



It may be mounted on a separate stand, or hung from 

 the projecting rod of the prime conductor. Fig. 31 

 represents a common style used in this way. 



It consists of three bells suspended from a brass rod; 

 the two outer ones by brass wires or chains, and the 

 central one by a silk cord ; a brass chain connecting it 



Fig. 31 Electric Chime. 



