SPIDERS. 301 



mingle, and when a pencil of threads is propelled, it ever 

 presents the appearance of a divergent brush. These are 

 electrical phenomena, and cannot be explained but on 

 electrical principles." 



"In clear, fine weather, the air is invariably positive; 

 and it is precisely in such weather that the aeronautic 

 spider makes its ascent most easily and rapidly, whether 

 it be in summer or in winter." " When the air is weakly 

 positive, the ascent of the spider will be difficult, and its 

 altitude extremely limited, and the threads propelled will 

 be but little elevated above the horizontal plane. When 

 negative electricity prevails, as in cloudy weather, or on 

 the approach of rain, and the index of De Saussure's hygro- 

 meter rapidly advancing towards humidity, the spider is 

 unable to ascend."* 



Mr. Murray had previously told us, that " when a stick 

 of excited sealing-wax is brought near the thread of sus- 

 pension, it is evidently repelled ; consequently, the electri- 

 city of the thread is of a negative character," while " an 

 excited glass tube brought near, seemed to attract the 

 thread, and with it the aeronautic spider."t His friend, 

 Mr. Bowman, further describes the aerial spider as " shoot- 

 ing out four or five, often six or eight, extremely fine webs 

 several yards long, which waved in the breeze, diverging 

 from each other like a pencil of rays." One of them " had 

 two distinct and widely-diverging fasciculi of webs," and 

 " a line uniting them would have been at right angles to 

 the direction of the breeze.":]: 



Such is the chief evidence in support of the electrical 

 theory ; but though we have tried these experiments, we 

 have not succeeded in verifying any one of them. The fol- 

 lowing statements of Mr. Blackwall come nearer our own 

 observations. 



5. " Having procured a small branched twig," says 

 Mr. Blackwall, " I fixed it upright in an earthen vessel 

 containing water, its base being immersed in the liquid, 



* Loudon's Mag. of Nat. Hist., vol. i. p. 322. 

 t Experim. Eesearclies in Nat. Hist., p. 130. 

 t Mag. Nat. Hist, vol, i. p. 324. 



