The day was hot and apparently
quite calm; yet under such circumstances, the atmosphere can never
be so tranquil as not to affect a vane so delicate as the thread of
a spider's web. If during a warm day we look either at the shadow
of any object cast on a bank, or over a level plain at a distant
landmark, the effect of an ascending current of heated air is
almost always evident: such upward currents, it has been remarked,
are also shown by the ascent of soap-bubbles, which will not rise
in an indoors room. Hence I think there is not much difficulty in
understanding the ascent of the fine lines projected from a
spider's spinners, and afterwards of the spider itself; the
divergence of the lines has been attempted to be explained, I
believe by Mr. Murray, by their similar electrical condition. The
circumstance of spiders of the same species, but of different sexes
and ages, being found on several occasions at the distance of many
leagues from the land, attached in vast numbers to the lines,
renders it probable that the habit of sailing through the air is as
characteristic of this tribe, as that of diving is of the
Argyroneta. We may then reject Latreille's supposition, that the
gossamer owes its origin indifferently to the young of several
genera of spiders: although, as we have seen, the young of other
spiders do possess the power of performing aerial voyages.
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