182 Mr. J. Black wall's Examination of 



in the air appears to have been mistaken by Mr. Virey for a 

 statement of their length. This is the more surprising, as I 

 have plainly indicated that they rarely exceed a. few feet in 

 longitudinal extent. 



I forbear to offer any comments on the inaccuracy and con- 

 fusion so conspicuous in M. Virey's survey of my opinions 

 concerning the insufficiency of winds, evaporation, and elec- 

 ti'icity to occasion extensive and simultaneous ascents of gossa- 

 mer-webs and spiders, and shall dismiss his review of my 

 memoir with a few strictures upon the following passage, 

 which clearly proves that not even my most careful exposi- 

 tions of the inferences I have deduced from exact experiments 

 have escaped perversion. "Cesanimaux" (spiders) " peu- 

 vent s'elever avec leurs tissus, et tantot retomber selon le 

 degre de gravite qui domine et les fait alors precipiter sur la 

 terre. D'ailleurs, certaines particules d'air rarefie ne peuvent- 

 elles pas se trouver comme renfermees dans le tissu gazeux de 

 ces araignees et prendre k la maniere des ballons un mouve- 

 ment ascendant? L'auteur s'attache a developper I'idee de 

 cette possibilite ; il montre que des araignees peuvent expulser 

 des fils a une certaine distance et les attacher par la matiere 

 gommo-visqueuse dont ils sont formes, a un lieu plus ou 

 moins eloigne." In experimenting with a view to demonstrate 

 the fact, tiiat spiders do not raise themselves into the atmo- 

 sphere by the exercise of any physical power with which they 

 are endowed, I repeatedly separated fiom the spinners of in- 

 dividuals, when they were ascending, the fine lines which con- 

 tributed to give them buoyancy. The result was conclusive. 

 The animals were quickly precipitated to the ground, and the 

 detached lines rose with increased velocity in consequence of 

 beincr acted upon by a diminished gravitating force. How 

 completely the true nature and object of this investigation 

 have been misunderstood by M. Virey appears from the first 

 sentence of the extract just given from his paper, upon which 

 it would be superfluous to offer any comment. After inquir- 

 ing, in the next place, whether the upward direction taken by 

 gossamer-webs may not be ascribed to the rarefied air in- 

 closed in them, M. Virey adds, that I have endeavoured to 

 develop this idea ; a piece of information which perplexes me 

 not a little, as I am wholly unconscious of having made any such 

 attempt. But the most remarkable circumstance remains to be 

 considered. It is assumed by M. Virey, in opposition to the fact 

 which I have uniformly and strenuously maintained, — a fact, 

 let it be remembered, confirmed by direct experiments care- 

 fully conducted and accurately detailed,— that I have rendered 

 it manifest that some spiders are capable of propelling their 



lines 



