754 C< 5 /. rot’s Experiments for 
long or fhort, will confequently be greater than the up- 
permoft fedlion of it; for the heat, by diflolving the 
moifture, produces a vapour lighter than air, which mix- 
ing with its particles, removes them farther from each 
other, increafes the elafticity of the general mafs, and 
diminifhes its fpecific gravity comparatively more than 
it doth that of the fedlion immediately above it, where 
there is lefs heat and lefs moifture. Hence I infer, that 
the equation for the air, in any afligned vertical, will 
gradually diminifh as the elevation of the place above 
the fea increafes, and that it will vanifh at the top of the 
atmofphere. This is in fome refpedt confirmed by the 
experiments on the expanfion of rare air; for from them 
it appears, when the particles are very far removed 
from each other, by a great diminution of preflure, as is 
undoubtedly the cafe in the higher regions of the atmo- 
fphere, they lofe a great part of their elaftic force. Thus 
the equation, anfwering to any particular temperature, 
above or below the zero of the fcale, at different heights 
above the furface, will, I apprehend, be exprefled by the 
ordinates to a curve of the hyperbolic order, whofe cur- 
end of his 8th chap, fur les difficulty a vainer e: and in that which follows, he 
gives proofs of the lightnefs of vapours with regard to air, faying, that they 
point out fire to be their vehicle. He afterwards quotes newton with refpe<3? 
to the lightnefs of a humid atmofphere compared with one that is dry- 
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