ART. III. On the Aerial Spider. By JOHN MURRAY, Esq. F.S.A. F.L.S. F.H.S. &c.

Sir,

I FEEL gratified by the favourable review of my Experimental Researches in Natural History (published by George B. Whittaker, Ave Maria Lane), in your Second Number. As far as I know, I have not ventured beyond the pale of sound and sober reasoning, in the true spirit of inductive science.

I have not presumed any thing in the shape of an opinion on the origin of light. It issues from a cloud which conceals its source. I have not attempted to penetrate its depth and labyrinth. I may, however, be permitted to add that Canton's phosphorus is merely composed of calcined shells, which a high temperature illuminates. There is a considerable brilliance excited, when the electric discharge is passed through this substance, and I have found the following a very pretty experiment: - Having strewn Canton's phosphorus (as it is called) over the surface of mercury contained in a shallow basin, Í immerse into the fluid metal one of the wires of an extensive galvanic battery, and bring the other polar wire in contact with its surface; at this moment the calcined particles become beautifully luminous, and continue to glow for some time after the positive and negative wires have been withdrawn. The nature of the subject treated of in my little volume, necessarily precluded a more full view of the nature and laws of light, and its multifarious sources, and what I have introduced can be only considered a very partial and superficial glance, as prefatory to the topic treated of, namely the light and luminous matter of the glowworm."

The object of this communication must, however, be chiefly confined to the ascent and flight of the aërial spider.

Mr. Blackwall's observations (Lin. Trans., vol. xv. part ii. p. 449. et seq.) on this curious question are cited, in opposition to my numerous and varied experiments; but I cannot admit that they possess much consequence or force. It does not appear that this author had seen an account of my experimental researches on the ascent of the little aëronaut; otherwise, he might have hesitated in committing himself to the Linnean Society, in the view he has endeavoured to sustain, but which, however, I believe is not new.

. M. Gay Lussac having found that soap bubbles would not ascend in a room, though their ascent is rapid in the open air, unhesitatingly ascribes their ascent to warm currents emanating from the surface of the ground; rooted in this opinion,

Mr. Blackwall concludes that the flight of the spider originates in a similar cause.

Contrary to the assertion, that "spiders have no power of propelling their webs without assistance from the wind," I fearlessly maintain that they can do so in an atmosphere in which the very leaf of the aspen remains motionless; and although their char volant obeys the direction of the breeze, this simple fact proves nothing in favour of the opinion advanced by Mr. Blackwall. The aeronautic spider can propel its threads both horizontally and vertically, and at all relative angles, in motionless air, and in an atmosphere agitated by winds; nay more, the aërial traveller can even dart its thread, to use a nautical phrase, in the "wind's eye." My opinion and observations are based on many hundreds of experiments; on favourable occasions I am constantly extending their amount; and as often do I find my deductions supported, namely, that the entire phenomena are electrical. My inferences, therefore, have not been hastily drawn.

When a thread is propelled in the vertical plane, it remains perpendicular to the horizontal plane, always upright, and when others are projected at angles more or less inclined, their direction is invariably preserved; the threads never intermingle, 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 except on electrical principles.

The specific gravity of the insect, with its web, are very superior to that of the atmosphere, and without some exotic power imparted to them, their rise in the atmosphere would be impracticable; and though a film inflated with heated, and of course, rarefied air, would certainly ascend, it is more difficult to undersand how a solitary thread, so fine, could be thus acted upon by any current of air, whether heated or not, so as to determine its buoyancy and ascent. And so far from the unattached cobwebs, which are occasionally seen to float in the atmosphere, having been" raised from the surface of the ground, by the action of air highly rarefied by a cloudless sun," such threads will be seen to fall in the warmest weather, and in all the unclouded radiance of the sunbeam. But this phenomenon presages rain, and is its precursor. The electrical character of the atmosphere has changed from positive to negative.

These interesting aeronauts sometimes rise with the rapidity of an arrow in the zenith of the observer; at other times, they are seen to float parallel with the plane of the horizon; and again, at variously inclined angles. Sometimes the ascent is extremely slow. An ascending current of warm air, it is conceivable, might effect a vertical movement; but how it could push VOL. I. No. 4.

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the insect along in the horizontal plane, is an enigma of more difficult solution.

I do not understand what Mr. Blackwall means, in what be says about the electricity of the atmosphere. I take it for granted, that it is seldom or never in a neutral state, with respect to electricity, being either positively or negatively electrical; in which view I am warranted, not merely by my own experiments, but of those conversant with atmospherical electricity. 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 summer or winter; I have often seen this in winter, during an intense frost, a circumstance which renders the action of warm currents of air, as accessory to its flight, something more than questionable. Our aeronaut may be met with in its descent over the Mer de Glace, as well as over the Lake of Geneva; and it will take flight as readily from a point over the Frozen Sea, as from the heated surface soil of the Valley of Chamouny. I am not yet convinced that there are calorific emanations from the Glacier de Bois.

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, with a falling barometer, and the index of De Saussure's hygrometer rapidly advancing towards humidité, the spider is unable to ascend. Towards evening the positive electricity of the air becomes feeble, and during night changes to negative; and at these periods the aeronauts descend from their skyey elevation to the earth. I have already clearly proved, experimentally, that the thread is imbued with negative electricity and such a thread, darted through the air with force and velocity, must of necessity become electrified, as a consequence of the friction it must suffer from the resisting medium it permeates. Such a thread, with its attachment, must ascend, until it is neutralised by its equivalent of positive electricity. These insects descend in vast numbers during the night to imbibe the dew, which condenses on the webs they weave among the grass; the attachment of globules of dew to the tips of the blades of grass, seems an electrical phenomenon, and as the thread must be considered a nonconductor of caloric, the fact of its being bedewed seems most easily referable to electricity.

I caught one of these aeronautic spiders a few days ago, the folding glass doors of the library room leading into the garden were open, and the insect being conveniently arranged, it

darted forth, from within the room, a lengthened thread diagonally upwards, and thus effected its ascent; a fact at complete antipodes with Mr. Blackwall's opinion.

The number of the aëronautic spiders occasionally suspended in the atmosphere, I believe to be almost incredible, could we ascertain their amount. I was walking with a friend on the 9th, and noticed that there were four of these insects on his hat, at the moment there were three on my own; and from the rapidity with which they covered its surface with their threads, I cannot doubt that they are chiefly concerned in the production of that tissue which intercepts the dew, and which, illuminated by the morning sun, "glitters with gold, and with rubies and sapphires." Indeed, I have noticed that, when the frequent descent of the aeronautic spider was determined, a newly rolled turnip field was, in a few hours, overspread by a carpet of their threads. It may be remarked that our little aeronaut is very greedy of moisture, though abstemious in other respects. Its food is perhaps peculiar, and only found in the superior regions of the sky. Like the rest of its tribe, it is doubtless carnivorous, and may subserve some highly important purpose in the economy of Providence; such, for instance, as the destruction of that truly formidable, though almost microscopically minute insect, the Fùria infernalis, whose wound is stated to be mortal. Its existence has been indeed questioned, but by no means disproved; that, and some others, injurious to man, or to the inferior creation, may be its destined prey, and thus our little aëronaut, unheeded by the common eye, may subserve an important good.

As connected with this question, I may mention that the electrical strata of the atmosphere, on Sunday the 6th inst., was singularly illustrated in the curious configurations of the dust on the pavement, being exhibited in a plumose form, resembling the figures described on a plate of rosin when touched by an electrified substance, and powdered rosin or sulphur, &c., is projected against them: an experiment we owe to Professor Lightenberg; while, I believe, the late Dr. Millar, of Edinburgh, was the first to notice these very interesting arborescent forms of dust, and refer the phenomenon to electricity. I noticed, also, on that day, that these configurations had their feathery image and impress in the sky, several of the clouds presenting that plumose form.

I now beg to quote an extract from a communication on the subject of the gossamer spider, made to me by my friend, J. E. Bowman, Esq. F.L.S.; and I shall at present content myself with it, not wishing to anticipate what may elsewhere appear on this subject. "We arrested several of these little

aëronauts in their flight, and placed them on the brass gnomon of the sundial, and had the gratification to see them prepare for, and recommence, their aërial voyage. Having crawled about for a short time, to reconnoitre, they turned their abdomens from the current of air, and elevated them almost perpendicularly, supporting themselves solely on the claws of their fore legs, at the same instant shooting 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, and strongly reflecting the sunbeams. After the insects had remained stationary in this apparently unnatural position for about half a minute, they sprang off from the stage with considerable agility, and launched themselves into the air. In a few seconds after they were seen sailing majestically along, without any apparent effort, their legs contracted together, and lying perfectly quiet on their backs, suspended from their silken parachutes, and presenting to the lover of nature a far more interesting spectacle than the balloon of the philosopher. One of these natural aëronauts I followed, which, sailing in the sunbeams, had two distinct and widely diverging fasciculi of webs, as in the annexed sketch (fig. 161.); and their position in the air

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was such, that a line uniting them would have been at right angles with the direction of the breeze."

In conclusion, permit me to mention, in reference to the glowworm, that I was quite aware of the opinion that had been entertained respecting the light of the glowworms, and reiterated by my reviewer; and the reason why I did not mention it was, that I held it to be unsatisfactory; my reasons are, that the insect, in its imperfect form of the larva, is gifted with light, as well as in its perfect and ultimate stage of metamorphosis. The winged male, as in the Lampyris itálica, carries its torch as well as the apterous female. Superadd to these, that the inference would not apply to the case of the crawling Scolopendra eléctrica on the one hand, or the winged Fúlgura lanternària on the other,

"That shoot like stars athwart the night."

July 16. 1828.

I have the honour to be, Sir, &c.

J. MURRAY.