i-iyfc Mr,. HENLT’a Experiments and 
whole time; and for fuch a purpofe I fhould recommend 
Mr. Co ventry’s, made with a number of circular pieces of 
iffue-paper, amounting to a certain weight, thoroughly 
» ■ » • ' r ■ 
heated and ftrung on a thread, 'kept feparate from each 
other by a fmall glafs bead, andfufpended on one of the 
ends of a lever, nicely poized, and turning freely : on its 
axis; the other end ferving as an index to a graduated 
fcale, on which it fliews the weight of the moifture im- 
bibed at any time by the papers.- This hygrometer, from 
its extreme fenfibility, I fhould choofe, 1 fay, to recom- 
mend for this purpofe, in preference to any other that 
I have ever feen. 
HAVING lately had o'ccafion to fhew the experi- 
ments with the coated Dutch plates to an excellent elec- 
trician (Mr. cavallo) and having charged them as high 
as I could, and feparated them I think rather more expe- 
ditioufly than ufual, I was- aftonifhed to find, that the 
very fame plates I have fo often mentioned were now 
charged, the one pofitively, the other negatively, on both 
furfaces. I then laid them together, and having made 
the difcharge as ufual, I feparated them, and found one 
of the plates negative on both fides, and the other plate 
pofitive on one furface, and negative on the other. Here 
was a new caufe of admiration, and I was utterly at a lofs 
to account for it, as the plates had in every inftance be- 
fore 
