§4 WT Bib OR ¥ “or 
ed during a hot fummer’s day, not only by the paflage of 
the fun’s dire&t rays through it, and by the refletinoof 
thofe rays from the furface of the earth into it; but chiefly, 
by the communication of the heat acquired by that furface 
to it: The electric capacity of that region of air would be 
increafed, both on account of the heat it undergoes, and 
‘of the rarefa€tion confequent upon that heat: It will then 
have lefs than its natural quantity, or the quantity it is 
naturally difpofed to receive and abforb in that ftate; it will 
confequently be, in the language of eleCtricians, negatively 
electrifed, or in a craving ftate, requiring and forcing fup- 
plies from all fubftances capable of affording them, pro-. 
vided it be itfelf in a condition to receive them. But, 
however craving, it cannot receive thofe fupples from the 
neighbouring regions of the atmofphere, while thofe re- 
gions feverally remain in the ftate of pure air, even fup- 
pofing the latter to poflefs more than their natural quanti- 
ties, and thereby as much difpofed to impart, as the for- 
mer is to receive them, without the intervention of non- 
electric conduétors ; and that, owing to the impermeability. 
of air, as fuch, to the electric fluid. This I fhall endeavour, 
rz. To illuftrate by experiments made with glafs. 2. To 
prove by experiments made upon air itfelf. 
1. Ifa pane of glafs be coated on both fides, by the ap- 
plication of plates of tin to them, the glafs may be charged 
in the fame manner as the Leyden phial; when, after the 
removal of the plates, no difcharge having previoully. 
taken place, both fides of the glafs will remain charged, 
one pofitively, the other negatively; the former having 
more than its zatural quantity, the latter being proportion- 
ably deficient, and in a craving ftate. Thete ftates both 
furfaces will obftinately maintain for along time: Nor do 
1 know of any method of reftoring the eleCtric equilibrium 
between them, but, either to immerfe the pane in water or 
fome other non-electric fluid, which will do it inftantly, 
and filently ; or to reapply the metalline coatings to both 
fides 
