ous combinations of tints and
those gorgeous ever-changing colours, which are a constant source of
admiration and delight to all who have the advantage of an uninterrupted
view to the west, and who are accustomed to watch for these not
unfrequent exhibitions of nature's kaleidoscopic colour-painting. With
every change in the altitude of the sun the display changes its
character; and most of all when it has sunk below the horizon, and,
owing to the more favourable angles, a larger quantity of the coloured
light is reflected toward us. Especially is this the case when there is
a certain amount of cloud. The clouds, so long as the sun is above the
horizon, intercept much of the light and colour; but, when the great
luminary has passed away from our direct vision, his light shines more
directly on the under sides of all the clouds and air strata of
different densities; a new and more brilliant light flushes the western
sky, and a display of gorgeous ever-changing tints occurs which are at
once the delight of the beholder and the despair of the artist. And all
this unsurpassable glory we owe to--dust!

A remarkable confirmation of this theory was given during the two or
three years after the great eruption of Krakatoa, near Java. The
volcanic debris was shot up from the crater many miles high, and the
heavier portion of it fell upon the sea for several hundred miles
around, and was found to be mainly composed of very thin flakes of
volcanic glass. Much of this was of course ground to impalpable dust by
the violence of the discharge, and was carried up to a height of many
miles. Here it was caught by the return currents of air continually
flowing northward and southward above the equatorial zone; and since,
when these currents reach the temperate zone, where the surface rotation
of the earth is less rapid, they continually flow eastward, the fine
dust was thus carried at a great altitude completely around the earth.
Its effects were traced some months after the eruption in the appearance
of brilliant sunset glows of an exceptional character, often flushing
with crimson the whole western half of the visible sky. These glows
continued in diminishing splendour for about three years; they were seen
all over the temperate zone; and it was calculated that, before they
finally disappeared, some of this fine dust must have travelled three
times round the globe.

The same principle is thought to explain the exquisite blue colour of