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 circumstar- 
ces, and indeed Mr. W. Ritchie has proposed threads of glass a 
pendants in his new balance of Torsion. ‘The current of air, or the 
sunbeam, is the primary exciting cause; and the electric charactel 
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ed, the buoyant cause is withdrawn, and the spider descends, at least 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 propuk 
sion of other threads; and the temporary buoyancy thus obtained 
from a partial evolution of electricity, the consequence of atmospherl¢ 
friction, its threads of attachment will then become a complete pa 
chute, and the rapid fall of the msect prevented. We have made 
experiments and observations recently to ascertain this point, and find 
that athread detached from the insect will receive electricity from 
solar ray, and ascend in the atmosphere in the sunbeam, when wi 
out the sphere of attracting substances, while a similar thread 10 the 
shade will not ascend at all; and we also find very light flocculi 
also, having absorbed electricity, ascend; and if such should enter 
the shade, they as immediately descend; and we have seen such m 
their descent brought by some casual circumstance into the suns " 
again, and as immediately afterwards effect a rapid ascent. Some 
times the phenomenon of ascent is accompanied by one or two dr 
vergent fasciculi.” ‘‘ Four or five, often six or eight, extremely fin¢ 
