grass, on account of the numerous centres of condensation this affords.
Dew, however, is now formed only on clear cold nights after warm or
moist days. The air near the surface is warm and contains much vapour,
though below the point of saturation. But the innumerable points and
extensive surfaces of grass radiate heat quickly, and becoming cool,
lower the temperature of the adjacent air, which then reaches
saturation point and condenses the contained atmosphere on the grass.
Hence, if the atmosphere at the earth's surface became super-saturated
with aqueous vapour, dew would be continuously deposited, especially on
every form of vegetation, the result being that everything, including
our clothing, would be constantly dripping wet. If there were absolutely
no particles of solid matter in the upper atmosphere, all the moisture
would be returned to the earth in the form of dense mists, and frequent
and copious dews, which in forests would form torrents of rain by the
rapid condensation on the leaves. But if we suppose that solid particles
were occasionally carried higher up through violent winds or tornadoes,
then on those occasions the super-saturated atmosphere would condense
rapidly upon them, and while falling would gather almost all the
moisture in the atmosphere in that locality, resulting in masses or
sheets of water, which would be so ruinously destructive by the mere
weight and impetus of their fall that it is doubtful whether they would
not render the earth almost wholly uninhabitable.

The chief mode of discharging the atmospheric vapour in the absence of
dust would, however, be by contact with the higher slopes of all
mountain ranges. Atmospheric vapour, being lighter than air, would
accumulate in enormous quantities in the upper strata of the atmosphere,
which would be always super-saturated and ready to condense upon any
solid or liquid surfaces. But the quantity of land comprised in the
upper half of all the mountains of the world is a very small fraction of