THREADS OF SPIDERS. 
371 
sign of coming rain ; that is, the spider feels the electrical 
changes of the atmosphere, which indisposed it for working. 
The most curious and intricate part of this subject has 
never been as yet discussed by naturalists. It is the con- 
sideration of the process by which it is possible for a spider 
to dart out a thread so long, and in a straight line. It is 
easy to comprehend how threads can be drawn out to a 
state of extreme exility, considering the glutinous substance 
of which they are composed ; but I consider it impossible 
for a spider to emit a thread of five or six feet long in a 
perfectly straight line, and with such rapidity that it is ac- 
complished in a few seconds ; without admitting that it 
has the power of ejecting also at the same time, either some 
gaseous matter, or some fluid resembling the electric ; and 
this, from what I have remarked, I am inclined to think is 
the fact. No mechanical force arising from the contraction 
of the muscles of the abdomen of the insect, could produce 
this phenomenon, without the assistance of some such fluid. 
For if a line of such tenuity were lighter than the atmo- 
spheric air, the end first thrown out would rise and cease to 
go forward ; if heavier than the air, it would fall ; if of the 
same weight with the air, still the part first ejected would be 
opposed by the density of the atmosphere, which would be 
quite sufficient to stop the progress of a body so light. 
I have sometimes observed spiders minutely, when the 
sun was shining clear, in the act of throwing out their lines, 
emit fourteen or fifteen filaments at once, and whilst these 
were flying so as to diverge considerably from each other, 
they evidently sent a stream of some fluid along the fila- 
ments, which both coalesced them into one line, and rendered 
that line straight. I have also remarked, that occasionally 
the geometric spider has thrown out half the length of the 
line it intended to strike upon some object, and after rest- 
ing a little, by another effort has lengthened it and sent it 
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