ELECTRICITY. 105 



dent to an audience at the Royal Institution, will form a 

 useful illustration : A Leyden jar, of one square foot coated 

 surface, has its interior connected with a Cuthbertson's elec- 

 trometer, between which and the outer coating of the jar 

 are a pair of discharging balls fixed at a certain distance 

 (about half an inch apart). Between the Leyden jar and 

 the prime conductor is inserted a small unit jar of nine inches 

 surface, the knobs of which are 0*2 inch apart. 



The balance of the electrometer is now fixed by a stiff 

 wire inserted between the attracting knobs, and the Leyden 

 jar charged by discharges from the unit jar. After a certain 

 number of these, say twenty, the discharge of the large jar 

 takes place across the half-inch interval. This may be 

 viewed as the expression of electrical power received from 

 the unit jar. The experiment is now repeated, the wire 

 between the balls having been removed, and therefore the 

 1 tip/ or the raising of the weight, is performed by the electri- 

 cal repulsion and attraction of the two pairs of balls. At 

 twenty discharges of the unit jar the balance is subverted, 

 and one attracting knob drops upon the other ; but no dis- 

 charge takes place, showing that some electricity has been lost 

 or converted into the mechanical power which raised the 

 balance. 



By another mode of expression, the electricity may be 

 supposed to be masked or analogous to latent heat, and it 

 would be restored if the ball were brought back without dis- 

 charge by extraneous force. If the discharge or other elec- 

 trical effects were the same in both cases, then, since the 

 raising of the ball or weight is an extra mechanical effort, 

 and since the weight is capable by its fall of producing elec- 

 tricity, heat, or other force, it would seem that force could be 

 got out of nothing, or perpetual motion obtained. 



The above experiment is suggestive of others of a similar 

 character, which may be indefinitely varied. Thus I have 

 found that two balls made to diverge by electricity do not 

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