296 
OfJ CHEMISTRY. 
by excited to radiate the heat it had received, it ought to do so, till 
it be cooled down to the temperature of the air, and no lower : But 
if—as indeed is the fact—the surface—especially that covered by her¬ 
bages—become cooler than the air, then there must be some agency 
in operation which is not manifested by the received theory: in 
other words, the reasoning made use of will not fully explain or elu¬ 
cidate the phenomena to which it is applied. The act of radiation 
implies a power that is concealed, and therefore very difficult to be 
appreciated: still however, it is known that, living vegetable bodies 
rank among the best conductors of electricity : they become sooner 
dewed; but they do not, by any means, appear to be active radia¬ 
tors of heat naturally. This conduction therefore, of heat, seems to 
depend upon that agency which stimulated the flow of the vegetable 
currents,—the electric vital fluid which induces the ascent of the 
sap ;—and if so, then, that radiation which brings down the tempe¬ 
rature of the vegetable body below that of the surrounding air, is an 
electrical phenomenon. 
A covering of clouds is inimical to the deposition of dew. 
Dr. Wells argues that dews appear only on calm, clear, nights, and 
that very little is ever deposited in opposite circumstances, and that 
little, only when clouds are very high. Dew is never seen in nights 
both cloudy and windy; and if, in the course of the night, the wea¬ 
ther from being serene, should become dark and stormy, dew which 
had been deposited, will disappear. When warmth of atmosphere 
is compatible with clearness, as is the case in southern latitudes, 
though seldom in our country, the dew becomes much more copious, 
because the air then contains much more moisture. 
The first part of this paragraph contains much truth, because it 
simply describes an effect; as to the cause, we must look for it in that 
which induces radiation. In a clear state of the atmosphere, cold 
generally increases, and dew is deposited. By some secret agency, 
the electrical surfaces are, I think, changed. The ground is in one 
case the attractor, and as the source of heat is etherial fire, that fire 
is first attracted by the points of the vegetable bodiesthose prime 
and most active conductors; and in this act, the particles of vapor 
are deprived of that fluid which had kept them in a state of repulsion 
—they coalesce by the abstraction of their electricity, and are depo¬ 
sited upon the conducting herbage; particularly,—and most copi¬ 
ously,—upon its pointed terminations. This conducting power, pos¬ 
sessed in so intense a degree by grass, and living vegetables, will 
explain ivhy the surface of the ground becomes coldest in their im¬ 
mediate vicinity—for they abstract all the etherial fire from the air 
