ON AERONAUTIC SPIDERS. 263 
circumstance or local peculiarity ; the ascent of gossa- 
mer, 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, 1826, for exam- 
ple, 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 eva- 
poration or electricity ; for, not to insist upon the 
probable, I had almost said absolute, insufficiency of 
these powers, considered as agents, experiments show 
that spiders do not select those periods for making 
an ascent when the evaporating force is unusually 
great or the electricity of the atmosphere is re- 
markable for its intensity*. I find, likewise, that 
when gossamer-webs and the larger species of Aéro- 
nautic Spiders are raised into the air with facility, 
the downy feathers of birds and seeds of plants are 
also carried upwards, whatever may be their electri- 
cal condition as induced by artificial means—a con- 
vincing proof that the buoyancy of these several 
objects does not depend upon the influence of elec- 
* The evaporating force may be determined by the atmo- 
meter, or from the temperature at which the aqueous vapour in 
the atmosphere begins to be condensed into water, and the tem- 
perature of the air (see the ‘ Memoirs of the Literary and Phi- 
losophical Society of Manchester,’ Ist series, vol. v. part 11, 
p. 588). The electrical state of the atmosphere is shown by 
Bennet’s gold-leaf electrometer. 
