270 ON AERONAUTIC SPIDERS. 
with the same success. Placed under bell-glasses, or 
in any situation where the air remained tranquil, they 
in vain attempted to make their escape from the twigs 
to which they were confined, notwithstanding their 
best endeavours to quit them were persisted in perti- 
naciously ; but in the disturbed atmosphere of an in- 
habited room most of them readily accomplished their 
object. I am confident, therefore, in affirming that 
the lines produced by spiders are not propelled from 
the spinners by any physical power possessed by 
those animals, but that they are invariably drawn 
from them by the mechanical action of external 
forces. 
Spiders, though placed on excellent conductors of 
electricity, such as metallic rods insulated by water, 
if exposed to a current of air, let out their lines with 
facility, and invariably in the direction of the breeze. 
The act is perfectly voluntary, and the lines, immedi- 
ately after they are emitted, nay, at the very time they 
are issuing from the spinners, if blown upon from 
any other quarter, instantly obey the new impulse 
thus imparted to them. I have tried this experiment 
on numerous occasions without once perceiving the 
slightest deviation from these results, which I, there- 
fore, regard as completely established. 
All spiders possessing an apparatus for spinning do 
not appear to be endowed with the instinct to let out 
their lines when placed on a twig insulated by water 
and exposed to a current of air; and as this is the 
