290 On the Vhcenomma cf the ElectrophoruSi 



3(1, Another plate of a circular form ; made either of 

 brass or of wood, ov even pasteboard covered with tinfoil r 

 this should be nearly of the same size, but rather smaller 

 than the inferior plate, and must be furnished with a glass 

 insulating handle, which by means of a brass or wooden 

 socket is screwed into its centre. 



For the sake of perspicuity it will be desirable to adopt 

 some short and appropriate appellation to distinguish each 

 of these parts from the otiters without circumlocution, as 

 they must frequently recur in the course of our inquiry f 

 and it will not perhaps be ea-^y to iinprove the nomencla- 

 ture of professor Robison in the Supplement to the Encif- 

 chptedla Brifannlm r 



1. The inferior plate, which constitutes the bottom or 

 support of the rest, and which in my apparatus is a flat 

 brass plate, 12 inches in diameter, made to screw upon a 

 glass insulating stand, we shall denominate — the sole. 



2. The electric substance to be excited, — the cake. 



3. The superior plate, 10 inches in diameter, with a glass 

 handle attached, for the pmrpose of imposing it upon and 

 removing it from th'e cake, — the cover. 



To each of these plates a' small wire is made to screw in, 

 adapted to suspend a pair of pith balls, by which means 

 the state of both sore and cover may be ascertained at the 

 same time, and in favourable eircum&tanees very minute 

 changes may be detected. 



The most obvious pharnamena exhibited by this instra- 

 ment are the following: 



The cake in contact with the sole must be excited by 

 friction, either with new flannel or dry warm silk, pre- 

 viously taking care to make the surface of the cake as dry 

 as possible : then, by means of its insulatins" handle, impose 

 the cover; then offer a conductor to the cover, and a spark 

 will pass between them; after which if the cover be elevated 

 or removed, by the extremity of its glass handle, from the 

 electric cake, it will yield a strong spark to any conducting 

 body. If the cover be replaced, a communication atforded 

 with the ground, 'by touching it with the finger or other- 

 wise, and again separating it, a second spark"^n)av be ob- 

 tained. And this process, with fresh excitation, maybe re- 

 peated for -hoars, if the apparatus be kept perfectly fret 

 from dust and moisture : and if these sparks be given to 

 the knob of a jar, it will become charged with positive elec- 

 tricity. 



It is evident, however, that these indications are not suf- 

 ficiently decisive to furnibh an accurate knowledge of the 



different 



