and on the north side of every house a high white wall would have to be
built to reflect the light and prevent that side from being in total
darkness. Even then we should have to live in a perpetual glare, or shut
out the sun altogether and use artificial light as being a far superior
article.

Much more important would be the effects of a dust-free atmosphere in
banishing clouds, or mist, or the "gentle rain of heaven," and in giving
us in their place perpetual sunshine, desert lowlands, and mountains
devastated by unceasing floods and raging torrents, so as, apparently,
to render all life on the earth impossible.

There are a few other phenomena, apparently due to the same general
causes, which may here be referred to. Everyone must have noticed the
difference in the atmospheric effects and general character of the light
in spring and autumn, at times when the days are of the same length,
and consequently when the sun has the same altitude at corresponding
hours. In spring we have a bluer sky and greater transparency of the
atmosphere; in autumn, even on very fine days, there is always a kind of
yellowish haze, resulting in a want of clearness in the air and purity
of colour in the sky. These phenomena are quite intelligible when we
consider that during winter less dust is formed, and more is brought
down to the earth by rain and snow, resulting in the transparent
atmosphere of spring, while exactly opposite conditions during summer
bring about the mellow autumnal light. Again, the well-known beneficial
effects of rain on vegetation, as compared with any amount of artificial
watering, though, no doubt, largely due to the minute quantity of
ammonia which the rain brings down with it from the air, must yet be
partly derived from the organic or mineral particles which serve as the
nuclei of every raindrop, and which, being so minute, are the more