192 
NATURAL I STORY 
lighter than air. But why thefe apterous infedis fhoiild that day 
take fuch a wonderful aerial excurfino, and why their webs fliould 
at once become fo grofs and material as to be confiderably more 
weighty than air, and to defcend with precipitation, is a matter 
beyond my fkill. If I might be allowed to hazard a fuppofition, 
I fliould imagine that thofe filmy threads, when firft Ihot, might be 
entangled in the rihng dew, and fo drawn up, fpiders and all, by a 
brifk evaporation into the regions where clouds are formed : and 
if the fpiders have a power of coiling and thickening their 
webs in the air, as Dr. Lijier fays they have, [fee his Letters to 
Mr. Ray] then, when they were become heavier than the air, 
they muft fall. 
Every day in fine weather, in autumn chiefly, do I fee thofe 
fpiders fliooting out their webs and mounting aloft : they will go 
olF from your finger if you will take them into your hand. Laft 
fummer one alighted on my book as I was reading in the parlour; 
and, running to the top of the page, and (hooting out a web, took 
it's departure from thence. But what I moft wondered at was, 
that it went off with confiderable velocity in a place where no air 
was ftirring ; and I am fure that I did not aflift it with my breath. 
So that thefe little crawlers feem to have, while mounting, fome 
loco-motive power without the ufe of wings, and to move in the 
air fafter than the air itfelf. 
LETTER 
