1 6 Mr. CavalIo’s Obfir vat ions on 
/ 
conducing fublhnce which conveyed the eledtricity to it, muff 
be difcontinued by means of a glafs (lick, or other infulatitig 
v -< m 
body ; then the plate A is removed, and the plate B is pre- 
fented to an ele 61 ro meter, in order to afeertain the quality ot 
the electricity j but if the eledtrometer be not affected by it, 
then the plate B is brought with its edge into contadt with 
another very fmall plate, which Bands upon a femi-condudting 
plane, after the manner of M. Volta’s condenfer*; which 
done, the fmall plate, being held by its initiating handle, is 
removed from the inferior plane, and is prefented to the elec- 
trometer : and it frequently happens, that the fmall plate will 
affedt the electrometer very fenfibly, and quite fufficient for 
the purpofe ; whereas the large plate itfelf {hewed no clear 
ligns of ele6tricity. 
If it be afked, why I ufe the femi-condudting plane for this 
fmall plate, and not for the large one ? the anfwer is, firft, be- 
caufe the large femi- conducing plane is incomparably more 
difficult to be procured than the fmall one; and, fecondly, 
becaufe the fmall plane may be eafily deprived of any acci- 
dental eledtricity which may adhere to it ; but the large one is 
more difficultly rendered fit for the purpofe, efpecially as the 
large plate ought in general to remain upon it a much longer 
time than the fmall plate is to remain upon its femi-condudting 
plane. 
The third and laff cafe is when the electricity to be afeer- 
tained is neither very confiderable in quantity, nor much con- 
denfed ; fuch is the eledtricity of the hair of certain animals, 
of the furface of chocolate when cooling, &c. In this cafe 
the heft method is to apply a metal plate, furnifhed with an 
* This fmall plate is nearly of the fize of a {billing, and the femi-condu<5ting 
plane is of wood covered with copal varniib. 
infulating 
