120 On North American Spiders. 



rise or fall, or distil their rains, agreeably to electric changes, so does 

 the gossamer spider effect its ascent or descend to the earth." 



" How does it happen that the ascent of the bird spider is slow at 

 one time, and rapid as an electric flash at another? vertical at one 

 period, and afterwards horizontal, or in variously inclined planes? on 

 one day requiring the propulsion of numerous threads, and the next 

 a solitary one affording buoyancy enough ? ascending at any period of 

 the day in one case, and on the following day incapable of effecting 

 an ascent at all, whether at morn, noon, or night, even with multiplied 

 threads, and when calorific emanations are assumed to be operative? 

 In fact, that a single upright thread should carry up the spider in the 

 vertical plane, on any such principle, seems to us utterly incompre- 

 hensible." 



" A spider's thread is an electric, and any such thread projected 

 through the air must necessarily become, by such resistance as is 

 occasioned by the atmosphere and consequent friction, imbued with 

 electricity. A thread of glass is electrified under such circumstan- 

 ces, and indeed Mr. W. Ritchie has proposed threads of glass as 

 pendants in his new balance of Torsion. The current of air, or the 

 sunbeam, is the primary exciting cause ; and the electric character 

 and condition of the thread are continued and preserved by the con- 

 tinuous action of the electricity of the solar ray. A cloud skreens 

 the disc of the sun ', and the exciting solar ray being thus intercept- 

 ed, the buoyant cause is withdrawn, and the spider descends, at least 

 when the entire electric energy is expended, though by the propul- 

 sion of other threads ; and the temporary buoyancy thus obtained 

 from a partial evolution of electricity, the consequence of atmospheric 

 friction, its threads of attachment will then become a complete para- 

 chute, and the rapid fall of the insect prevented. We have made 

 experiments and observations recently to ascertain this point, and find 

 that a thread detached from the insect will receive electricity from the 

 solar ray, and ascend in the atmosphere in the sunbeam, when with- 

 out the sphere of attracting substances, while a similar thread in the 

 shade will not ascend at all ; and we also find very light flocculi will 

 also, having absorbed electricity, ascend ; and if such should enter 

 the shade, they as immediately descend ; and we have seen such in 

 their descent brought by some casual circumstance into the sunshine 

 again, and as immediately afterwards effect a rapid ascent. Some- 

 times the phenomenon of ascent is accompanied by one or two di- 

 vergent fasciculi," '' ' Four or five, often six or eight, extremely fine 



