TRANSACTIONS OF THE SECTIONS. 387 



one of which is fixed, the other moveable, the latter being sus- 

 pended from the periphery of a wheel. The distance between 

 the conductors is either constant or variable, according to the 

 conditions of the experiment, and the force is estimated on a 

 graduated arc in terms of a known standard of weight or other- 

 wise in degrees. 



The unit of measure consists of a small electrical jar, having 

 a discharging electrometer, and inverted on the prime conductor 

 of the machine. The quantity accumulated is measured by its 

 repeated explosions, in consequence of electricity passing from 

 the outer coating. 



When it is required to communicate comparative quantities 

 of electricity to simple insulated conductors, sparks are drawn 

 by means of an insulated transfer plate from an insulated jar 

 charged by the preceding method with a known quantity. 



By the aid of these instruments, the author has arrived at 

 some new results in electricity, which appear to be not un- 

 worthy of notice. 



In disposing different quantities of electricity on insulated 

 conductors of similar form and dimensions, he finds that the at- 

 tractive force is directly as the square of the quantity, the sur- 

 face being constant ; and inversely as the square of the surface, 

 the quantity being constant ; being similar to the results which 

 he had already arrived at in examining the disposition of elec- 

 tricity on coated jars*. 



On comparing those results with the striking distance of a 

 given accumulation, he finds that the quantity of electricity re- 

 quisite to produce a discharge is invariably as the square of the 

 distance directly ; that is to say, when the distance is twice as 

 great, there is four times the quantity of electricity accumulated 

 at the instant of the discharge, all other things remaining the 

 same ; and this is true, whether the accumulation take place on 

 simple insulated conductors or on coated jars. 



The above laws are general when the conductors or jars are 

 in every respect similar, but they do not obtain vmder every 

 possible kind of extension of the same surface. The author 

 finds, with Professor Volta, that extension in length increases 

 the capacity of a given conductor. In examining the capacities 

 of plane surfaces for electricity, he finds the capacity to be as 

 the linear dimensions of the plate inversely, the area being con- 

 stant ; and if the linear dimensions be the same, it varies in an 

 inverse ratio of the area. The extent of edge or boundary of 

 the plate, however, has not in itself any influence on the capa- 



* Memoirs of the Plymouth Institution. 



C> f, 



/V Vv ^V 



