244 



ROUND THE YEAR 



they stood, a little more of their liquid gum, and com- 

 mitting themselves to these bridges of their own 

 constructing, they passed over them in safety, drawing 

 a second line after them as a security in case the first 

 gave way, and so effected their escape. Such was in- 

 variably the result when the Spiders were placed 

 where the air was liable to be sensibly agitated : I 

 resolved therefore to put a bell-glass over them ; and 

 in this situation they remained seventeen days.evidently 

 unable to produce a single line by which they could 

 quit the branch they occupied, without encountering 

 the water at its base ; though on the removal of the 

 glass they regained their liberty with as much celerity 

 as in the instances already recorded. This experi- 

 ment, which, from a want of due precaution in its 

 management has misled so many distinguished 

 naturalists, I have tried with several of the Geometric 

 Spiders, and always with the same success. Placed 

 under the bell-glass, or in any close vessel, they in 

 vain endeavoured to make their escape from the 

 branch to which they were confined ; but in the 

 disturbed air of an inhabited room, they readily 

 accomplished their object." 



The rising of gossamer has been attributed to the 

 low specific gravity of the Spider and to imaginary 

 causes which will bear no investigation. Since 

 Blackwall's researches it has been agreed that light 

 currents of air are sufficient to explain the rise of fine 

 filaments. It is not a question of buoyancy, but of 

 surface in proportion to weight. The webs rise for 

 the same reason that fine dust rises in moving air, and 

 fine sediment in moving water. It is for the same 



