( 47 ) 



which till then had not been vifible, and on the 2.5th of January they 

 began to fpin webs in the fame manner as full grown fpiders. 



I iiad hitherto been at a lofs to conceive how this 2:reat number of 

 young Spiders could be fupplied with n jurifliment, confidering that 

 the natural food of this creature is the fubflance of other infe6ls ; but 

 I now perceived that they had fed on the barren eggs which had been 

 left in the glafs, and they afterwards devoured one another till they 

 were reduced to a very few in number. 



I have often compared the fize of the thread fpun by full grown 

 Spiders with a hair of my beard. For this purpofe I placed the 

 thickell part of the hair before the microfcope, and from the moft 

 accurate judgment I could form, more than an hundred of fuch 

 threads placed fide by fide could not equal the diameter of one fuch 

 hair. If then we fuppofe fuch an liair to be of a round form, it 

 follows that ten thoufand of the threads fpun by the full grown 

 Spiders when taken together, will not be equal in fubftance to the 

 fize of a fingle hair.* 



To this if we add that fourf- hundred young Spiders at the time 



* This is found by multiplying the number of Spiders' threads, conftituting the diameter 

 of the hair (which the Author computes to be one hundred) into itfelf, the contents of 

 cylinders (which round threads may be called), being in the fame proportion as the fquares 

 of their diameters — 



therefore 100 diameters of the thread 



multiplied by the fsme number 100 



the fquare will be 10,000 the proportionate fize of the hair, 

 and this being multiplied by 400 the fuppofcd bulk of a young Spider com= 



4,000,000 

 pared wiih an old one, gives four millions, the proportion afligned by the Author to the 

 young Spiders' threads. 



The Author's manner of computing thefe very minute dimenfions, is fully explained in 

 the Introduilion, 



f The difference in the fize of garden Spiders in Spring and Autumn, muft have been 

 noticed by almoft every one, and the Author in his computation, confiders them as fpheri- 



