106 aq Se EO RAYS oF 
fame réafon, would be driven up with violence through a 
like narrow vent, yet not with the fame impetuofity, nor 
to the fame height as if forced through this funnel into = 
pure vacuum. 
That the atmofphere over large tracts of fea or land may 
thus become fpecifically lighter than that over the fur- 
rounding regions, will be evident, if we confider, 1. That 
heat has a natural tendency to rarefy and expand the air 
upon whichit acts. 2. That the atmofphere over our heads 
does not confift of mere elementary air, but is an univer- 
fal receptacle of all the heterogeneous vapors and effluvia. 
that are perpetually exhaling from every fubftance that 
exifts upon the face of the earth, whether animal, veget- 
able or mineral. 3. That, by the cafual difpofition of 
thefe vapors and effluvia in the atmofphere, the air, which 
is, of itfelf, naturally enough difpofed to acquire heat from 
the paflage of the fun’s rays through it, may become more 
difpofed to imbibe and retain that heat, in one region, than. 
in another in its neighbourhood; which, from the inter- 
vention of clouds, or from its purity and freedom from. 
thofe fteams and vapors with which the former is charged,. 
* may, in a great degree, retain its natural coolnefs and, 
denfity, while the other becomes heated, rarefied and ex- 
panded, and is thereby rendered: fpecifically lighter. 
That thefe different affeCtions of the atmofphere adfu- 
ally take place, and difpofe the air, at one time and in one 
place, even in the fame feafons of the year, to imbibe and. 
retain the heat excited by the fun’s rays, more than at 
another, is not a matter of mere conjecture ; but, what- 
ever the caufe may be, is notorious to all perfons of ob-. 
fervation. 
Thefe things being premifed, I beg leave to obferve fur- 
ther, that fome parts of the ocean are liable to long and’ 
extenfive calms, during the continuance of which the heat 
is fearcely tolerable. Where thefe take place the air mutt: 
neceflarily undergo proportional changes in its denfity and: 
electric 
