528 LECTURE LIV. 



glass which covers the electrometer, opposite to the extremities of the 

 leaves, prevents the communication of any electricity to the glass, which 

 might interfere with the action of the instrument. When the balls of an 

 electrometer stand at the distance of 4 degrees, they appear to indicate a 

 charge nearly 8 times as great as when they stand at one degree : a charge 

 8 times as great in each ball producing a mutual action 64 times as great 

 at any given distance, and at a quadruple distance a quadruple force ; in 

 the same manner a separation of 9 degrees is probably derived from an 

 intensity 27 times as great as at 1. In Lane's electrometer* the magnitude 

 of a shock is determined by the quantity of air through which it is obliged 

 to pass, between two balls, of which the distance may be varied at plea- 

 sure ; and the power of the machine may be estimated by the frequency of 

 the sparks which pass at any given distance. It appears from Mr. Lane's 

 experiments, that the quantity of electricity required for a discharge is 

 simply as the distance of the surfaces of the balls, the shocks being twice 

 as frequent when this distance is only -^ of an inch as when it is T V Mr. 

 Volta says, that the indications of Lane's and Henley's electrometer agree 

 immediately with each other ; but it seems difficult to reconcile this result 

 with the general theory. Sometimes the force of repulsion between two 

 balls in contact is opposed by a counterpoise of given magnitude, and as 

 soon as this is overcome, they separate and form a circuit which discharges 

 a battery ; whence the instrument is called a discharger. (Plate XL. Fig. 

 564... 568.) 



It must be confessed that the whole science of electricity is yet in a very 

 imperfect state : we know little or nothing of the intimate nature of the 

 substances and actions concerned in it : and we can never foresee, without 

 previous experiment, where or how it will be excited. We are wholly 

 ignorant of the constitution of bodies, by which they become possessed of 

 different conducting powers ; and we have only been able to draw some 

 general conclusions respecting the distribution and equilibrium of the sup- 

 posed electric fluid, from the laws of the attractions and repulsions that it 

 appears to exert. There seems to be some reason to suspect, from the 

 phenomena of cohesion and repulsion, that the pressure of an elastic 

 medium is concerned in the origin of these forces ; and if such a medium 

 really exists, it is perhaps nearly related to the electric fluid. The identity 

 of the general causes of electrical and of galvanic effects is now doubted by 

 few ; and in this country the principal phenomena of galvanism are 

 universally considered as depending on chemical changes ; perhaps, also, 

 time may show, that electricity is very materially concerned in the essen- 

 tial properties, which distinguish the different kinds of natural bodies, as 

 well as in those minute mechanical actions and affections which are 

 probably the foundation of all chemical operations ; but at present it is 

 scarcely safe to hazard a conjecture on a subject so obscure, although Mr. 

 Davy's experiments have already in some measure justified the boldness of 

 the suggestion. 



* Ph. Tr. 1767, p. 451. 



.0* 



