xxxii Of the Method of rendering very fenjible 
elude this paper with mentioning a few ideas I entertain 
relating to the atmofpherical eledtricity. 
The experiments hitherto made, though not numerous, yet 
concur to fhew, that the vapours of water, and in general the 
parts of all bodies, that are feparated by volatilization, carry 
away an additional quantity of eledtric fluid as well as of ele- 
mentary heat, and confequently that thofe bodies, from the con- 
tadt of which the volatile particles have been feparated, remain 
both cooled and eledtrified negatively : from which it may 
be deduced, that whenever bodies are refolved into volatile 
elaftic fluid, their capacity for holding eledtric fluid is aug- 
mented, as well as their capacity for holding common fire, or 
the calorific fluid. This is a ftriking analogy by which the 
fcience of electricity throws fome light upon the theory of 
heat, and alternately derives light from it ; I mean on the doc- 
trine of latent or fpecific heat, the firft notions of which were 
fuggefted by the admirable experiments of Dr. black and 
Wilke, and which has been afterwards much elucidated by 
Dix crawford, who followed the experiments of Dr. irwin. 
By following this analogy it feems, that as the vapours on 
their condenfing, lofe patt of their latent heat, on account of 
their capacity being diminifhed, fo they part with fome eledtric 
fluid. Hence originates the pofitive eledtricity, which is always 
..more or lefs predominant in the atmolphere, when the fky 
is clear, viz. at that height where the vapours begin to be con- 
denl'ed. fVccordingly, the atmofpherical eledtricity is ftronger 
in fogs, in which cafe the vapours are more condenfed, fo as 
to be almoft reduced into drops, and is ftill ftronger when thick 
fogs become clouds. 
Hitherto we have accounted for the pofitive atmofpherical 
electricity ; but it is eafy to account for clouds negatively elec- 
trified ; for when a cloud, politively eledtrified, has been once 
formed, its fphere of adtion is extended a great way round, fo 
that if another cloud comes within that fphere, its eledtric 
fluid, agreeably to the well known laws of eledtric atmofpheres, 
mufl retire to the parts of it which are the remoteft from the 
firfl cloud ; and from thence the eledtric fluid may be commu- 
nicated 
