THEORY OF THE DEW. 
155 
that of almost vapourless transparency, and the maximum temperature from 75° 
to 80°. At such a period, wherein evaporation must have been at its maximum, 
millions of tons of water would daily pass into the atmosphere without producing a 
diminution of its transparency. Yet so far from clouds or rain resulting from this 
measureless absorption of vapour, the dew itself was precipitated during the clearest 
nights in extremely diminished quantities. 
Radiation takes place from heated surfaces into any cooler medium ; thus, an 
iron steam-tube, passing through a vessel of water, will radiate or diffuse its heat 
among the particles of water which surround it. The hot-water pipes of a forcing- 
house will radiate heat into, and warm the atmosphere of the building ; but this 
radiation will not produce any phenomena which can elucidate the theory of dew. 
A basin or striking-glass, inverted, will receive moisture from the surface of the 
ground, covered with herbage, and exhibit it in the state of condensed water-drops ; 
but it will do the same and produce the same results when placed on the surface of 
hot, sandy, and parched ground. Radiation, so viewed, is little else than another 
term for evaporation or the evolution of steam. But the radiation of our theorists is 
referred to the agency of vegetable organised bodies, as if it were the result of some 
faculty they possess of conducting and carrying off heat from the surface of the earth, 
and from their own organisation, till reduced to a degree of temperature much lower 
than that of the surrounding air. 
But do not the advocates of this hypothesis overlook the organic structure 
of plants, and the peculiar conductive powers with which they are endowed ? A tuft 
of grass, presented with its pointed extremities to the prime conductor of an electri- 
fying machine, or to the ball of a charged jar, will draw off the charge silently ; 
hence, we may safely conclude that herbage attracts and neutralises the electricity of 
the atmosphere around it. We must admit that the air abounds with watery vapour ; 
and this very admission implies the repulsion of the particles by some energetic 
natural agent. What, then, is that agent ? The inquiry is of deep interest ; but 
analogy appears to furnish the ready answer. It should appear that the vegetable 
creation is destined to perform some of the grandest functions of nature, by con- 
necting the energies of the great agents, solar-light, air, water, and earth. If we 
investigate the structure and uses of the leaves and their serratures — of thorns, 
bristles, and prickles — of the sharp divisions of sepals, petals, and the fructiferous 
organs of flowers, we may perceive, by copious induction of facts, that grass, herbage, 
shrubs, and trees — those " best of radiators," which are " the soonest dewed " — 
constitute, in fact, an assemblage of so many conducting points — a series of the most 
perfect conduits of natural electricity, which not only maintains the intercourse 
between the earth and its atmosphere, but, in so doing, promotes and effectuates the 
attraction, distribution, and elaboration of all the vegetable fluids. Can the phenomena 
of the dew — that is, the condensation of atmospheric moisture — be otherwise more 
clearly elucidated ? And why should trees and herbage condense so great a volume 
of water ? Why should ground, newly dug, be covered with hoar-frost, when 
