SPIDERS. 347 



matter, which was instantly carried out in a hne, 

 consisting of four finer ones, with a velocity equal, 

 or nearly so, to that with which the air moved, as 

 was apparent from observations made on the motion 

 of detached hnes similarly exposed. The spiders, 

 in the next place, carefully ascertained whether their 

 lines had become firmly attached to any object or 

 not, by pulling at them with the first pair of legs; 

 and if the result was satisfactory, after tightening 

 them sufficiently, they made them pass to the twig; 

 then discharging from their spinners, which they 

 applied to the spot where they stood, a little more of 

 their liquid gum, and committing themselves to these 

 bridges of their own constructing, they passed over 

 them in safety, drawing a second line afler them, as 

 a security in case the first gave way, and so effected 

 their escape. 



" Such was invariably the result when 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 Vvhich 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 experiment, which, from want of due pre- 

 caution has misled so many distinguished naturalists, 

 I have tried with several geometric spiders, and 

 always with the same success."* 



Mr Blackwall, from subsequent experiments, says 

 he is " confident in affirming, that in motionless air, 

 spiders have not the power of darting their threads 

 even through the space of half an inch."| The fol- 



* I. inn. Trans., vol. xv. p, 456. 

 + Mag. Nat IJist., vol. ii. p. 397. 



