how Spiders effect their aerial Excursions. 455 
comparatively still air of a room without fire, both the lines and 
webs descend slowly to the floor, the latter falling with the 
greater degree of velocity. 
Were these productions lighter than atmospheric air, or were 
the spiders capable of effecting an ascent without the help of 
adventitious aid, a calm though cloudy day might answer their 
purpose ; but as considerable warmth is required to produce an 
ascending current of rarefied air strong enough to bear them 
from the earth, a bright as well as still day is indispensable. 
Founded on results obtained from an experiment which has 
been frequently made, but never conducted with sufficient care, 
is the belief entertained by many eminent entomologists that 
spiders can forcibly propel or dart out threads from their papilla. 
Now as this process would, contrary to my own experience, im- 
ply the exercise of a physical power peculiar to these creatures ; 
and as attempts have been made to explain on this principle the 
fabrication of their webs in situations where their ordinary mode 
of proceeding could not be employed, I determined to repeat 
the experiment from which so strange a conclusion has been 
deduced. With this view, having procured a small branched 
twig, 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 mo- 
tion of detached lines similarly exposed. The spiders, in the 
VOL. XY. 3 N next 
