1817.) from one Point to another. 309 
that in aroom, where the air is quite still, they should be able to 
make their threads fly straight out or upwards with such rapidity. 
We would be apt to imagine that in a substance so very light, the 
part which was sent out last would move quicker than the part 
which was before it, and consequently get into curves or knots. It 
makes it, therefore, more probable, that these spiders must have 
the power of throwing out some stream of air, or some subtle fluid, 
as the line keeps moving as straight out as a fishing-rod, as long as 
the spider pleases, and never is inclined to fall down, but always 
rises.* While one was guiding its thread which it had sent out to 
some length, being suspended as usual by a short line from the top 
of the straw, I observed that when I blew upon the thread that was 
flying, it raised the spider up a little. By catching hold of the 
flying thread with my finger, I tried to draw the spider upwards ; 
and | drew it several feet from the place where it hung, it having 
let out a line behind it to that length. I conceived that in this 
way, with the help of other circumstances, they might be carried 
through the air, by a thread of some length, to a great distance. 
Nor was this conjecture wrong; for having kept a geometrical 
spider running for some time upon my hand, which was stretched 
out a little, it dropped down about six inches from the point of my 
finger by its thread, and immediately emitted a pretty long line at 
a right angle with the one by which it was sespended. The thread 
which was flying outwards quickly rose upwards, and carried the 
spider along with it. When the spider had ascended as far above 
my finger as it was before beneath it, it let out the thread which 
was attached to my finger, and continued flying smoothly upwards 
till it nearly reached the roof of the room, when it veered about to 
the side, and alighted on the wall. When it flew its motion was 
smoother and quicker than when a spider runs along the thread. If 
they are able to fly so easily in a room, they will evidently fly with 
much more facility in the open air. These spiders generally drop 
down from the place on which they rest some inches by their thread 
before they shoot out their flying line ; that by hanging in the air 
they may be enabled to feel more sensitively whether the line they 
have let out may be buoyant enough to carry them up, or whether 
it fixes on any object while they pull it in. They may fly in this 
way to any length, or to any height; for as the line lengthens be- 
hind them, the tendency to rise increases. 
_ I found also that another species of spider, with a bright yellow 
body, and very short legs, had the power of shooting out threads, 
but not to the same extent as the geometric spider. 
I tried several other kinds of spiders, but none of them seemed 
to have the power of making their escape, remaining eight or ten 
days on the straw. They were as lively after being without food 
* If the torpedo has the power of throwing out electricity, may net the spider 
have the same power to a certain extent, though exercised in a different way? 
6 
