82 iD A SEO PREY HOF 
pofitive, the other.in a negative ftate; when it will ex 
actly refemble the curious ftone called the tourmalin; by 
fome lapis electricus, which doctor Prieftley fays * “ has 
“ always, at the fame times a pofitive and a negative elec-. 
& tricity ; ; one of its fides being in one ftate, and the other 
“ in the oppofite ;”? which does not depend upon the ex- 
ternal form “ of the ftone.” But the truth of this Os 
on muft be determined by future experiments. 
That the electrical ftate of the air is liable to be aff ected 
by heat, is further evident from a courfe of experiments 
which were made by the abbé Mazeas, with an apparatus 
that was conftrudted folely with a view of determining the 
electricity of the atmofphere, anno 1753. With this ap- 
paratus the abbé obferved, that from the 17th of June, when 
he began his experiments, the electricity of the air was 
fenfibly felt every day, from fun rife till feven or eight 
o'clock in the evening, when the weather was dry ; but 
that in the drieft uzghts of that fummer he could difcover 
no figns of electricity in the air, nor till the morning, 
when the fun began to appear above the horizon, and . 
that “ they vanifhed again in the evening, about half an 
“ hour after fun fet;” and further, ‘ that the Strongeft 
“ common electricity, of the atmofphere, during the fum- 
“ mer, was perceived in the month of Fuly on a very dry 
«“ day, the heavens being very clear, and the fun extreme 
“ Ly hot.” 
Now, as this electricity of the air was fenfible only dur=. 
ing day light, no eleétricity being difcoverable therein even 
in the drief# mghts, and as thie air exhibited the fronge/t 
fiens of electricity when the fun fhone extremely hot ; is 
not the conclufion unavoidable, that heat fomehow affects 
the eleftric capacity of air, either enlarging it, and there-. 
by difpofing the air to attra, receive and abforb greater 
quantities of eledtric matter than it is capable of abforbing 
in its natural ftate; or fuperadding to its natural quantity 
more than it can abforb, and thereby difpofing it to throw 
off 
* Page 299. >} Page 342. 
