while this decrease has
been going on in the east, and in the morning, the light has presented
itself with increasing brightness in the west, and in the evening, and
pursues its course until the end of February at about the same rate of
motion. In March, it is slow, and travels through not more than one
sign, and fades in April, and is lost in May, to reappear again at the
end of summer, and perform the same route.

Lengthened twilight is not favourable to the appearance of the
zodiacal light; it can, therefore, be observed successfully in the
temperate latitudes only by patient and long-continued watching. But
in tropical regions, the deep azure of the sky, and the brief
twilight, give it a distinctness and luminosity never witnessed
elsewhere. In Egypt, we are told it is clearly 'visible every night,
except when the light of the moon is too great, from January to June;'
and in India its appearance is described as that of 'a pyramid of
faint aurora-borealis like light' usually preceding the dawn. Humboldt
tells us, that he has seen it shine with greater brightness than the
Milky Way, from different parts of the coast of South America, and
from places on the Andes more than 13,000 feet above the sea-level.

'Those who have dwelt long,' he writes, 'in the zone of palms, must
retain a pleasing remembrance of the mild radiance of this phenomenon,
which, rising pyramidally, illumines a portion of the unvarying length
of the tropical nights.' And once, during a voyage from Lima to
Mexico, he saw it in greater magnificence than ever before. 'Long
narrow clouds, scattered over the lovely azure of the sky, appeared
low down in the horizon, as if in front of a golden curtain, while
bright varied tints played from time to time on the higher clouds: it
seemed a second sunset. Towards that side of the heavens, the light
diffused appeared almost to equal that of the moon in her first
quarter.'

The zodiacal light can hardly fail of having been observed by
astronomers in the past ages of the world; but the earliest known
mention of it occurs in the _Britannia Baconica_, published by
Childrey in 1661. The writer says: 'There is another thing which I
recommend to the observation of mathematical men--which is, that in
February, and for a little before and a little after that month--as I
have observed for several years together--about six in the evening,
when the twilight hath almost deserted the horizon, you shall see a
plainly dis