NATURAL HISTORY OF SELBORNE. 197 



webs from their tails so as to render themselves buoyant, and 

 lighter than air. But why these apterous insects should that day 

 take such a wonderful aerial excursion, and why their webs should 

 at once become so gross and material as to be considerably more 

 weighty than air, and to descend with precipitation, is a matter 

 beyond my skill. If I might be allowed to hazard a supposition, 

 I should imagine that those filmy threads, when first shot, might 

 be entangled in the rising dew, and so drawn up, spiders and all, 

 by a brisk evaporation, into the regions where clouds are formed : 

 and if the spiders have a power of coiling and thickening their 

 webs in the air, as Dr. Lister says they have [see his Letters to 

 Mr. Ray], then, when they were become heavier than the air, they 

 must fall. 



Every day in fine weather, in autumn chiefly, do I see those 

 spiders shooting out their webs and mounting aloft : they will go 

 off from your finger if you will take them into your hand. Last 

 summer one alighted on my book as I was reading in the parlour; 

 and, running to the top of the page, and shooting out a web, took 

 its departure from thence. But what I most wondered at was, 

 that it went off with considerable velocity in a place where no air 

 was stirring ; and I am sure that I did not assist it with my 

 breath. So that these little crawlers seem to have, while mounting, 

 some locomotive power without the use of wings, and to move in 

 the air faster than the air itself. 1 



NOTE TO LETTER XXIII. 



1 The appearance of the gossamer-covered fields will be familiar to all who live 

 in the country. It seems clear that the " locomotive power " of the tiny spiders 

 is due solely to the movement of the atmosphere. On the quietest days, if you 

 will wet your finger and hold it up, you will find it grow sensibly cooler on one 

 side than the other, and on that side is there a faint wind blowing. If you 

 will then watch the spiders, you will see them shoot out long silvery threads, 

 which will incline to leeward, and presently the spiders will let go their hold 

 of the grass, and launch themselves into the air, floating away on the slightest 

 movement of it. 



