THUNDER STORMS. 07 
of travellers who have vifited the tops of very high moun- 
tains, even under the line. ‘The greater the heat which 
this body of air acquires below, the greater degree of ra- 
refaction it undergoes, and the higher, of confequence, it 
afcends in the atmofphere, where the cold is proportion- 
ably more fevere than is ufual near the furface of the earth. 
But though it was the heat which it acquired below that 
firft rarefied and expanded it, it will by no means be pro- 
portionably recondenfed by the cold which it meets with 
in its afcent; for as the heat which occafioned its rarefac- 
tion decreafes upon that account, the preflure of the in- 
cumbent atmofphere upon it decreafes as it rifes, whereby 
its denfity may, upon the whole, remain nearly the fame ; 
if fo, may we not fuppofe its electrical ftate alfo, previous 
to the formation of the cloud, to continue nearly the fame? 
For fhould this warm air afcend all together as in a body, 
without intermixing with the denfer furrounding air through 
which it rifes, as a bubble of air does in any other fluid, 
and as ¢his air probably would in a calm feafon, the den- 
fer parts of the atmofphere eafily giving way to it, till it 
arrives at that region the denfity of which is equal to its 
own, where it would be at reft; fhould this, I fay, be the 
cafe, it would not, even in that cold region, cool fo fud- 
denly as to undergo any immediate change in its electrical 
ftate, from the natural coldnefs of the region ; neither 
would it be from condenfation, its denfity remaining nearly 
the fame, as obferved above. 
But when the cloud is formed, or rather when a number 
of clouds are forming in the neighbourhood of each other, 
and joining their forces preparatory to the tempeft, a ge- 
neral confufion takes place in the atmofphere; various and 
even contrary currents of air flowing promifcuoufly hither 
and thither, as is evident from the vifible irregular moti- 
ons of detached parts of the clouds. In this general effort 
of nature to reftore an equilibrium, fome of thefe aerial 
currents will probably introduce air, which having been 
ull 
