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E X T R A CTS_NATURAL HISTORY. 
NATURAL HISTORY. 
Theory of Rain. —The commonly received opinion is, that the water which 
evaporates from the surface of the earth is held in a state of chemical solution 
in the air, which ascends into higher regions, where the moisture is precipitated in 
the form of clouds, which are sustained there by the joint agency of heat and 
electricity, and the deposition of rain is the result of the electrical action of the 
clouds upon each other. The atmosphere, at the elevation of a few hundred 
yards, is at a tolerably uniform temperature with that near the surface of the 
ground, and therefore the condensation of the evaporated moisture must take 
place at a considerable height. In tropical countries this condensation in the 
form of clouds is not so frequently witnessed as in our colder climates, where 
the temperature of the air is continnually subject to variation. 
That evaporation does take place at all temperatures, when the air is tolerably 
dry, may be easily shown, by placing a cup on the surface of water, containing 
dried potash, or fused chloride of calcium; either of these substances will deli¬ 
quesce with great rapidity, or if concentrated sulphuric acid be substituted, it will 
speedily absorb nearly half its bulk of water; the vapour which appears to rise 
from water and low ground after sunset, is merely the moisture precipitated from 
the air upon the earth, cooled by radiation.— Field's Nat. Mag. 
Answers to the objections respecting the Theory of Rain, extracted from the 
Field Nat. Mag. and inserted page 185. 
Answer to objection First. —The reason of this seems to be, that the vapour 
rises imperceptibly, both above and below 60 degrees, and is condensed in the 
atmosphere when it is below that temperature. Thus the vapour is impercepti¬ 
ble in the neck of a Florence flask boiling over a lamp, though clearly seen 
above it, when the temperature is less. Again, when a draught of cold air dries 
a wet pavement, no steam is perceptible on the surface, though five or six feet 
above it may be felt as a sensible dampness on the clothes and linen. 
Answer to objection Second. —In this case the temperature is raised both in the 
air, and on the surface of the earth. We know not what becomes of water when 
raised in the atmosphere, by a high or very low temperature, as in both cases it 
is imperceptible, though its particles are no doubt affected by heat or the absence 
of heat, the one expanding it into dispersed and incoherent particles, the other 
condensing it into the form of hail or snow. By the absence of caloric, which at 
any temperature above the freezing point, is sufficient to keep it in a state of 
fluidity. 
Answer to objection Third. — This would undoubtedly be the case were water 
raised by the heat of 300 degrees in usual summer heat, but this is not the case 
in any part of our globe. Again, in all cases of evaporation we mpst make al¬ 
lowance for currents of air which disperse the vapours and separate its particles, 
counteracting its tendency to gravitate. 
Answer to objection Fourth —This proves the effect of condensation of the 
aqueous particles by cold, but does not disprove their rarefaction by heat, which 
would keep their particles divided, and thus prevent condensation. 
Answer to objection Fifth. —Here the agency of increased temperature in the 
surrounding air renders the vapour invisible, as with our breath, which is only 
