how Spiders effect their aérial Excursions. 453 
change their quarters, to a feeling of insecurity occasioned by 
their proximity to one another ;—the prodigious numbers which 
in favourable seasons are usually congregated together affording 
the more powerful individuals an opportunity, seldom neglected 
by these voracious creatures, of making an easy prey of the 
weaker: and this opinion is strengthened, if not confirmed, by 
the fact, that they are chiefly animals which have not arrived at 
maturity that undertake these migrations. 
I have asserted, that when the spiders which produce gossamer 
perform their aérial journeys, they are borne upward by an 
ascending current of rarefied air acting on the slender lines 
which proceed from their spinners. I shall now endeavour to 
prove that this curious atmospherical phænomenon, which well 
deserves the attention of meteorologists, affords them the only 
available means of accomplishing their object; and that the 
hypotheses previously adverted to are quie. irreconcileable with 
facts, and consequently must be erroneous. | 
It has been already stated, that gossamer is never seen floating 
in the air except in calm sunny weather ; its buoyancy, therefore, 
evidently does not depend upon the agency of winds, usually so 
called : indeed it is probable that winds never do take an upward 
direction, unless influenced by some extraordinary circumstance 
or local peculiarity ; the ascent of gossamer, on the contrary, is 
frequently observed to take place over a great extent of country 
on the same day. It was noticed on the Ist of October, for 
example, in England, Wales, and Ireland. — 
Ifa satisfactory explanation of this interesting fact cannot be 
derived from the operation of winds, it is still less likely to be 
deduced from the action of evaporation or electricity ; for, not 
to insist upon the probable, I had almost said absolute, insuf- 
ficiency of these powers considered as agents, experiments show 
that the spiders do not select those periods for making an ascent 
when 
