On JVorth American Spiders. 113 



air, and never descend except driven by a wind ; wherefore 'tis cer- 

 tain. And 'tis as certain, that what swims and ascends in the air is 

 lighter than the air, as that what ascends and swims in water is hght- 

 er than Water. So that if we should suppose any such time, where- 

 in the air is perfectly calm, this web is so easily dravvn out of the 

 spider's tail, that if the end of it be once out, barely the levity of it 

 is sufficient to draw it out to any length 5 wherefore if it don't hap- 

 pen that the end of this web, h c, catches by a tree or some other 

 body, 'till there is so long a web drawn out, that its levity shall be so 

 great as more than to counterbalance the gravity of the spider, or so 

 that the web and the spider, taken together, shall be lighter than such 

 a quantity of air as takes up equal space, then according to the uni- 

 versally acknowledged laws of nature, the web and the spider togeth- 

 er will ascend, and not descend, in the air : as when a man is at the 

 bottom of the v/ater, if he has hold of a piece of timber so great, 

 that the wood's tendency upwards is greater than the man's tendency 

 downwards, he together with the wood will ascend to the surface of 

 the water. And therefore, when the spider perceives that the web 

 be is long enough to bear him up by its ascending force, he lets go 

 his hold of the web a b, Fig. 3, and ascends in the air with the web 

 b c. If there be not web more than enough, just to counterbalance 

 the gravity of the spider, the spider together with the web will hang 

 in equilibrio, neither ascending nor descending, otherwise than as the 

 air moves. But if there is so much web, that its greater levity shall 

 more than equal the greater density of the spider, they will ascend 

 till the air is so thin, that the spider and web together are just of an 

 equal vii'eight with so much air. And in this way. Sir, I have multi- 

 tudes of times seen spiders mount away into the air, from a stick in 

 my hands, with a vast train of this silver web before them ; for, if 

 the spider be disturbed upon the stick by shaking of it, he will pres- 

 ently in this manner leave it. And their way of working may very 

 distinctly be seen, if they are held up in the sun, or against a dark 

 door, or any thing that is black. 



" Now, Sir, the only remaining difficulty is, how they first put out 

 the end of the web b c, Fig. 3, out of their tails. If once the web 

 is out, it is easy to conceive how the levity of it, together with the 

 motion of the air may draw it out to a great length. But how should 

 they first let out of their tails, the end of so fine and even a string ; 

 seeing that the web, while it is in the spider, is a ceitain cloudy li- 

 quor, with which that great bottle tail of theirs is lillcd ; which im- 



VoL. XXI-^No. 1. 15 



