138 ANNUAL OF SCIENTIFIC DISCOVERY. 



and the prime conductor is inserted a small unit-jar of 9 square 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 discharging from the unit-jar. After a certain number of these 

 (twenty -two in the experiment performed in the theatre of the Institution), the 

 discharge of the large jar takes place across the -^-inch interval; this may be 

 viewed as the expression of the electrical power received from the unit-jar. The 

 experiment is now repeated, the wire between the balls having been removed, 

 and therefore the " tip " or the raising of the weight is performed by the elec- 

 trical repulsion and attraction of the power of two pairs of balls ; at twenty- 

 two discharges of the unit-jar, the balance is subverted, and one knob drops 

 upon the other, but no discharge takes place, showing that some electricity has 

 been lost, or converted into mechanical power, which raises the balance. 



By another mode of expression, the electricity may be supposed to be 

 masked or analogous to latent heat, and would be restored if the ball were 

 brought back, without discharge, by extraneous force. 



The experiment is believed to be new, and to be suggestive of others of a 

 similar character, which may be indefinitely varied. 



Thus, two balls made to diverge by electricity should not give to an electro- 

 meter the same amount of electricity as if they were, whilst electrified, kept 

 forcibly together : an experiment of this sort I have made since my lecture, in 

 the following manner: 



To a thick brass wire, 2 feet long, insulated and terminated by knobs, are 

 suspended by fine platina wires, two pairs of discs of paper coated with tin- 

 foil, and 4 inches in diameter. The apparatus is electrized in a dry atmosphere 

 by sparks from a machine, and the discs of each pair respectively diverge. 



To one of the pairs a silk thread is attached, by which the discs can be 

 forcibly approximated. As often as this is done the divergence of the other 

 pair increases. 



Another mode of showing the same effect is the folio whig: 



On the top of an ordinary gold-leaf electroscope place two brass plates, such 

 as are commonly used for a condenser, connect them by a long fine wire, and 

 electrify them by a rubbed rod of glass or sealing wax, so that the gold leaves 

 diverge. 



Now raise the upper plate by a glass handle : the leaves collapse in pro- 

 portion as it is raised, and again diverge as it is depressed. It should be recol- 

 lected that the plates are electrified by the same electricity, and are always 

 metallically connected by the fine wire, in which respect this differs from ordi- 

 nary induction experiments. 



It may be said that here the mechanical force is given by the hand ; but 

 this is only in part, the repellent effect of electricity does part of the work and 

 should be therefore expended ; it is analogically as though a man were to add 

 his force to the piston rod of a steam engine, which would not prevent the loss 

 of heat by dilating steam. 



