-’*• On the Method of rendering very fenfible 
1 icco mmended it as a thing efleiitial to obferve * : but this 
c.ircum fiance is Hill more eflential when the fame apparatus is 
lo ferve as a condenfer of electricity. 
Laftly, it deierves to be repeatedly and particularly ob- 
luved, that the ref nous plate, when it is to be ufed for our 
experiment, fhould be quite free from any the lead electricity, 
otherwile the experiments cannot be depended upon. If’ 
therefore, the refinous plate has been excited before, fo as 
to remain in fome mealure electrified, all poflible care fhould 
he taken to deprive it of that electricity, which however is 
not eaf ly done. The mod effectual method of doing it to ex- 
pole the refinous plate to the hot rays of the fun or to the 
the,, lo that its lurtace may be (lightly melted, by which means 
it will entirely lole its eleCtricky -f. The flame of a candle, 
or . a P! e . ce °/ paper, will eafily deprive the refin of its elec- 
tricity, it its lurtace be pafled over the flame. In order to ob- 
ierve whether the refinous plate is quite free from any electri- 
city, the metal plate mud be laid upon it, there it mud be 
touched with a finger, and afterwards, being lifted up after the 
ulual manner, it mud be prefented to a fine hair; for if the 
hair is not attracted, you may conclude, that the refinous plate 
has no electricity, and conlequently the apparatus is fit to be 
uled as a condenfer of electricity. 
9. Were I alked, to what degree the eleCtricity might be 
condenfed, or how much the eleCtrical phenomena could be 
* ^ ee the two letters addrefied to Dr. priestley, and puhiiflied in the Scclta 
* Cjpufculi inter ejjanti of Milan for the year 1775. 
t It has been believed for a long time, that to heat, and efpecially to melt, 
ulphur and refins, was lulficient to excite in them fome eledricity ; but except the 
tourmalin and iome other hones, which are really excited by heat alone, the 
re fins and 1 ulphur never become elednfied by that means, except when tbev have 
by fome means or other fuffered any fridion. The miflake, as Father beccaria 
oblerved, was occafioned by this, viz. that even the leaft fridion of the hand 
f Other body, is fufficient to excite fuch fublhnces in thofe favourable circum- 
itances ; without which Iridion, thofe fubftances, melted and left to cool by 
themlelves, are fo far from acquiring any eledricity, that they lofe every vefW 
ot it in eale thej, were excited before the fufion, as nuay be eafily proved bv 
experiment: nor ought this to appear wonderful, lince fufion 0; a tfrono debtee 
• 1 heat renders every body a condudor of eledricity, b 
increafed 
