WINDS, AND THEIR CURRENT EFFECTS ON VEGETATION. 
83 
essential to its continued im ponderosity, and a consequence of its separation, bears 
with it the element which imparted its volatility, leaving the body from which it 
emanated with a deduction of temperature equal to the share it contains. 
Those who study such matters, will not fail to perceive in the above imperfect 
description, the reason of the extraordinary force of steam. Were an air-tight 
vacuum to be heated to the highest possible degree, the materials circumscribing it 
might be consumed, but they would never explode. On the other hand, if a close 
vessel be partly filled with water, and the water caused to boil, the intense heat 
accumulated in the vapour would create such an amazing expansion, that the 
bursting of the vessel would be inevitable. 
We can hardly deem it needful, after what has been advanced, to mention that 
evaporation is not invariably a result of the external action of heat. Perhaps the 
most commonly-received notion of this great natural process is, that it is brought 
about solely by the active influence of the sun ; and this is so far correct, that 
perspiration is most copious under immediate solar agency. Nevertheless, seeing 
that drought mB,y be excited by other means, and that the main incentive to 
evaporation is a dry atmosphere, however it may be produced, we learn that 
vapour is exhaled either by the concurrent operation of solar and inherent heat, or 
by the simple effort of the latter to attain a greater altitude. 
To assist the reader in appreciating our conclusions, we shall now show how 
excessively cold winds are injurious to plants, and what are the conditions which 
increase their prejudicial consequences. Creating a remarkable degree of aridity, 
they must, in conformity to the doctrines propounded, occasion a proportionate 
amount of evaporation ; and, as in the instance of radiation already analyzed, this 
being borne to other districts as soon as evolved, there is none of the mitigation 
which would result from the gradual saturation of a stagnant air, but an incessant 
and equal efflux is maintained. It will follow, therefore, that when a plant sur- 
charged with moisture, or with its members in the fittest state for exhaling it, is 
subjected to winds, its exhalations will, cceteris paribus^ be most abundant, and the 
reduction of its temperature most seriously extensive. 
An instant clue is thus obtained to the injury spoken of in the outset of this 
paper. The unusual quantity of water which fell last autumn, has rendered vege- 
tation so successively turgid, that when this fluid was drawn off by a process 
which, while it engendered cold, brought no supply of heat to modify its influence, 
plants could not be otherwise than reduced to the lowest ebb of vitality, or com- 
pletely killed. In other words, because chilling winds, and not solar agency, were 
the instruments in relieving vegetation of its unwonted load of moisture, it was 
deprived of much heat that was absolutely essential to sustain life, and its organi- 
zation was thus materially disarranged or ruptured. 
Other conditions unquestionably combined with the foregoing in this work of . 
destruction. The only one we shall point out is the state of excitation which had 
been induced by a long period of mildness, whereby, in those plants which had 
