170 
sensible heat are required to raise water to the boiling point, 
under the atmosphere, and then to convert the water into 
steam, 940° more, sensible heat, are absorbed — this latter 
disappears, as sensible heat, (call it latent, specific, or other- 
wise) but when the steam is condensed and returns to 
water, then the same 940° reappears as sensible heat, Now 
we all know that such absorption and redischarge of heat is 
continually taking place, in the evaporation from the earth’s 
surface, by the action of solar heat. This heat then to the 
extent, at least, of 940° becomes latent in the steam, or 
invisible aqueous vapour, at the surface, and the same heat 
is again given out in the upper air, where the vapour is 
condensed into clouds or fogs. The experiments and esti- 
mates of Dr. Halley, enable us in some degree to perceive 
the stupendous scale of the daily ascent of water in 
vapour,* into the higher regions of the air, when its heat; 
both sensible and latent, is evolved. But this heat, does 
mot thence return to the earth, as sensible heat, because the 
temperature above the clouds is always at or near the 
freezing point. What then becomes of these vast floods of 
sensible heat, that enter the vapour at the surface and 
entirely disappear in those cold regions above ? The plain 
answer seems to be that the entire heat, so ascending and 
disappearing, simply passes into its normal, or elemental 
form, of neutral heat. On this view of the mutations of 
heat, we see why it must become more or less redundant in 
the upper air, according to the varying rates of evaporation. 
These mutations of heat, will account for its becoming 
redundant, or of higher elastic tension, as a neutra] element, 
Dr. Halley (in the “Philosophical Transactions”) “has shown that 
more than five thousand millions of tons of water, ascend, in vapour, 
daily, from the surface of the Mediteranean only.” Now it follows that a 
mighty force must be exerted in raising this stupendous weight of water, (to 
the height of some thousand feet) against the force of gravity, in the water, 
and the elastic force of pressure by the air. But this evaporating force is 
solely due “ to the known relations of heat and water,” and is (as before said) 
a chemical force. 
