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candles at noon-day, while the country enjoys the brilliant light
of an unclouded sun.
It has been a matter of surprise to some, that a cloud should
seem to remain stationary upon the summit of a high mountain,
when the air was moving at a brisk rate. The warm air of a valley
being impelled up the inclined plane of a mountain side, into a
colder region, is not able to support the same quantity of
vapour; and a cloud is formed in consequence: and although the
individual particles of which it is composed, are continually
moving forward with the wind; yet by a perpetual accession of
vapour on one side, and dispersion on the other, the cloud may
continue to occupy the same place, and appear to a distant
observer as stationary; although its component parts are
successively changed: and in this manner may the materials of a
cloud be transported invisibly from the summit of one mountain to
that of another.
When a dense cloud settles upon a mountain, the wind frequently
blows from it on one side with an increased momentum, while on
the opposite side its motion is retarded; and a shower commencing
on the hills, is generally preceded in its course by a squall -
the air, displaced by the falling rain, making its escape along
the vallies where it meets with the least resistance.
By the unequal distribution of vapour in the atmosphere, the
visual rays passing through it suffer a variable degree of
refraction; on which account it
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