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 therefore
give us no light. We should have bright glaring sunlight or intensely
dark shadows, with hardly any half-tones. From this cause alone the
world would be so totally different from what it is that all vegetable
and animal life would probably have developed into very different forms,
and even our own organisation would have been modified in order that we
might enjoy life in a world of such harsh and violent contrasts.

In our houses we should have little light except when the sun shone
directly into them, and even then every spot out of its direct rays
would be completely dark, except for light reflected from the walls. It
would be necessary to have windows all around and the walls all white;