how Spiders effect their aerial 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 aftordin^' 

 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 aerial 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 phœnomenon, Avhich well 

 deserves the attention of meteorologists, aflbrds them the only 

 available means of accomplishing their object; and that the 

 hypotheses previously adverted to are quite 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 1st of October, for 

 example, in England, Wales, and Ireland. 



If a 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- 

 ticiency of these powers considered as agents, experiments show 

 that the spiders do not select those periods for making an ascent 



when 



