466 MOTIONS OF INSECTS. 
Thomson’s Annals of Philosophy, under the signature of Carolan, has 
given some curious observations on the mode in which some geometric 
spiders shoot and direct their threads, and fly upon them; by which it 
appears that as they dart them out they guide them as if by magic, emitting 
at the same time a stream of air, as he supposes, or possibly some subtile 
electric fluid. One, which was running upon his hand, dropped by its 
thread about six inches from the point of his finger, when it immediately 
emitted a pretty long line at a right angle with that by which it was sus- 
pended, This thread, though at first horizontal, quickly rose upwards, 
carrying the spider along with it. When it had ascended as far above his 
finger as it had dropped before below it, it let out the thread by which it 
had been attached to it, and continued flying smoothly upwards till it 
nearly reached the roof of the room, when it veered on one side and 
alighted on the wall. In flying, its motion was smoother and quicker than 
when a spider runs along its thread. He observes, that as the line lengthens 
behind them, the tendency of spiders to rise increases. I have myself 
more than once observed these creatures take their flight, and find the 
following memorandum with respect to their mode of proceeding : —“ The 
spider first extends its thighs, shanks, and feet into a right line, and then 
elevating its abdomen till it becomes vertical, shoots its thread into the 
air, and flies off from its station.’”’ It is not often, however, that an ob- 
server can be gratified with this interesting sight, since these animals are 
soon alarmed. I have frequently noticed them —for at the times when 
these webs are floating in the air they are very numerous—on the vertical 
angle of a post or pale, or one of the uprights of a gate, with the end of their 
abdomen pointing upwards, as if to shoot their thread previously to flying 
off ; when, upon my approaching to take a nearer view, they have lowered 
it again, and persisted in disappointing my wish to see them mount aloft. 
The rapidity with which the spider vanishes from the sight upon this oc- 
casion, and darts into the air, is a problem of no easy solution. » Can the 
length of web that they dart forth counterpoise the weight of their bodies; 
or have they any organ analogous to the natatory vesicles of fishes ?, which 
contributes at their will to render them buoyant in the air? Or do they 
rapidly ascend their threads in their usual way, and gather them up, till 
having collected them into a mass of sufficient magnitude, they give them 
selves to the air, and are carried here and there in these chariots? I must 
here give you Mr, White’s very curious account of a shower of these webs 
that he witnessed. On the 2ist of September, 1741, intent upon field 
diversions, he rose before daybreak ; but on going out he found the whole 
face of the: country covered with a thick coat'of cobweb, drenched with 
dew, as if two or three setting-nets had been drawn one over the other. 
When his dogs attempted to hunt, their eyes were so blinded and hood- 
winked that they were obliged to lie down and scrape themselves. ‘This 
appearance was followed by a most lovely day. About nine. m.a showet 
of these webs (formed not of single floating threads, but of perfect flakes, 
some near an inch broad, and five or six long) was observed falling from 
very elevated regions, which continued without interruption during the 
whole of the day; and they fell with a yelocity which showed that they 
were considerably heavier than the atmosphere, When the most elevated 
station in the country where this was obseryed was ascended, the webs 
1 No. lii, 306, 9 Cuvier, Anat, Comp. i. 504, 
