ions,
keeping up the condensation and discharging, day and night and from one
year's end to another, an amount of water equal to that which falls
during the heaviest tropical rains. All of the rain that now falls over
the whole surface of the earth and ocean, with the exception of a few
desert areas, would then fall only on rather high mountains or steep
isolated hills, tearing down their sides in huge torrents, cutting deep
ravines, and rendering all growth of vegetation impossible. The
mountains would therefore be so devastated as to be uninhabitable, and
would be equally incapable of supporting either vegetable or animal
life.

But this constant condensation on the mountains would probably check the
deposit on the lowlands in the form of dew, because the continual
up-draught toward the higher slopes would withdraw almost the whole of
the vapour as it arose from the oceans, and other water-surfaces, and
thus leave the lower strata over the plains almost or quite dry. And if
this were the case there would be no vegetation, and therefore no animal
life, on the plains and lowlands, which would thus be all arid deserts
cut through by the great rivers formed by the meeting together of the
innumerable torrents from the mountains.

Now, although it may not be possible to determine with perfect accuracy
what would happen under the supposed condition of the atmosphere, it is
certain that the total absence of dust would so fundamentally change the
meteorology of our globe as, not improbably, to render it uninhabitable
by man, and equally unsuitable for the larger portion of its existing
animal and vegetable life.

Let us now briefly summarise what we owe to the universality of dust,
and especially to that most finely divided portion of it which is
constantly present in the atmosphere up to the height of many miles.
First of all it gives us the pure blue of the sky, one of the most
exquisitely beautiful colours in nature. It gives us also the glories
of the sunset and the sunrise, and all those brilliant hues seen in high
mountain regions. Half the beauty of the world would vanish with the
absence of dust. But, what is far more important than the colour of sky
and beauty of sunset, dust gives us also diffused daylight, or skylight,
that most equable, and soothing, and useful, of all illuminating
agencies. Without dust the sky would appear absolutely black, and the
stars would be visible even at noonday. The sky itself would t