1 4 Mr. Cavallo’s Obfervations on 
negative ; I communicated fome negative eleCtricity to the 
plate A , with a view of deftroying its inherent politive elec- 
tricity. This plate A being now electrified negatively, but fo 
weakly as juft to affeCt an electrometer, I began doubling; but 
after having doubled three or four times, I found, by the help 
of an electrometer, that the communicated negative eleCtricity 
in the plate was diminifhed inftead of being increafed ; fo that 
fometimes it vanifhed entirely, though by continuing the ope- 
ration it often began to increafe again, after a certain period. 
This fhews, that the quantity of eleCtricity, which however 
fmall it may be, remains in a manner fattened to the plates, 
will help either to increafe or to diminifh the accumulation or 
multiplication of the communicated eleCtricity, according as it 
happens to be of the fame, or of a different nature. 
After all the above-mentioned experiments made with thofe 
doubling or multiplying plates, we may come to the following 
conclufion, viz. that the invention is very ingenious, but their 
ufe is by no means to be depended upon. It is to be wifhed, 
that they may be improved, fo as to obviate the weighty ob- 
jections that have been mentioned in the preceding pages, the 
hrft defideratum being to conflruCt a fet of fucli plates as, when 
no eleCtricity is communicated, they will produce none after 
having performed the operation of doubling for a certain num- 
ber of times. 
Upon the whole, the methods by which fmall quantities of 
eleCtricity may be afcertained with precifion are, as far as I 
know, only three. If the abfolute quantity of eleCtricity be 
fmall and pretty well condenfed, as that produced by a fmall 
tourmalin when heated, or by a hair when rubbed, the only 
effectual method of manifefting its prefence, and afcertaining 
its quality, is to communicate it immediately to a very delicate 
electrometer, 
