96 ay HW EVO-R-Y: oF 
fufficiently heated and rarefied, will in like manner afcend, 
its place being fupplied by the denfer air from all quarters 
without the limits of the calm. This heated and confe- 
quently (granting the principles of the prefent theory) 
ele&trical air, when raifed to a certain height in the at- 
mofphere, may become as well adapted to the formation 
of a thunder cloud, from the vapors which are perpetual- 
ly exhaling from the fea, as the air over the land under 
the like circumftances. Wherefore, in fome latitudes in 
all feafons, and perhaps in all latitudes in different feafons 
of the year, thunder ftorms may as well happen at fea, 
even at remote diftances from land, as afhore. 
I now proceed. to confider an obje€tion which may be 
raifed againft the foregoing theory, which I fhall firft ftate 
in its full force, and then endeavour to give a fatisfactory 
anfwer to it. 
Objection. If the eletrification of that body of air in 
which a thunder cloud is formed depends upon the heat 
it has previoufly acquired, whence is it that thunder ftorms 
are frequently attended with fhowers of hail, which hail 
is fometimes fo large as to indicate its defcent from the 
coldeft regions of the atmofphere? 
Anfwer. Sir aac Newton afferts from experiments of 
his own, that ‘ the denfity of the air in the atmofphere of 
“ the earth is as the weight of the whole zacumbent air.” 
Confequently the air gradually decreafes in denfity from 
the furface of the earth to the top of the atmofphere. The 
body of air which is fuppofed in this theory to be qualifi- 
ed by the action of heat upon it, to become a proper /uzb- 
ftratum for the formation and {upport of a thunder cloud, 
is thereby expanded and rarefied, and thence becomes fpe- 
cifically higher than it was before: It therefore afcends 
till it arrives at that height in the atmofphere at which the 
air is naturally, from its fituation, of the fame rarety with 
itfelf; and there it refts in equilibrio. This region is ex- 
treamly cold at all feafons, as appears from the teftimonics 
of 
