Mr. Murray had previously told us, that "when a stick of excited
sealing-wax is brought near the thread of suspension, it is evidently
repelled; consequently, the electricity of the thread is of a negative
character," while "an excited glass tube brought near, seemed to
attract the thread, and with it the aëronautic spider."[FC] His friend,
Mr. Bowman, further describes the aërial spider as "shooting out four
or five, often six or eight, extremely fine webs several yards long,
which waved in the breeze, diverging from each other like a pencil of
rays." One of them "had two distinct and widely-diverging fasciculi of
webs," and "a line uniting them would have been at right angles to the
direction of the breeze."[FD]
Such is the chief evidence in support of the electrical theory; but
though we have tried these experiments, we have not succeeded in
verifying any one of them. The following statements of Mr. Blackwall
come nearer our own observations.
5. "Having procured a small branched twig," says Mr. Blackwall, "I
fixed it upright in an earthen vessel containing water, its base being
immersed in the liquid, and upon it I placed several of the spiders
which produce gossamer. Whenever the insects thus circumstanced were
exposed to a current of air, either naturally or artificially produced,
they directly turned the thorax towards the quarter whence it came,
even when it was so slight as scarcely to be perceptible, and elevating
the abdomen, they emitted from their spinners a small portion of
glutinous matter, which was instantly carried out in a line, consisting
of four finer ones, with a velocity equal, or nearly so, to that with
which the air moved, as was apparent from observations made on the
motion of detached lines similarly exposed. The spiders, in the next
place, carefully ascertained whether their lines had become firmly
attached to any object or not, by pulling at them with the first pair
of legs; and if the result was satisfactory, after tightening them
sufficiently, they made them pass to the twig; then discharging from
their spinners, which they applied to the spot where they stood, a
little more of their liquid gum, and committing themselves to these
bridges of their own constructing, they passed over them in safety,
drawing a second line after them, as a security in case the first gave
way, and so effected their escape.
"Such was invariably the result when spiders were placed where the air
was liable to be sensibly agitated: I resolved, therefore, to put a
bell-glass over them; and in this situation they remained seventeen
days, evidently unable to produce a single line by which they could
quit the branch they occupied, without encountering the water at its
base; though, on the removal of the glass, they regained their liberty
with as much celerity as in the instances already recorded.
Public-domain text, read in full here on John Shaqi.
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