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PART II.

REVIEWS.

ART. I. Experimental Researches in Natural History. By John Murray, F.S.A. F.L.S. &c. London. 12mo, pp. 177. 6s. Reviewed by M.

THE author of this little work has chosen some of the most remarkable phenomena in nature for description and illustration. His first two subjects are on the light of the glow-worm and the luminosity of the sea. Both are treated with much practical knowledge, gained, it would appear, from extensive and patient investigation. He first speaks of the nature of light, and declares himself a follower of Newton, in the opinion that it is "material, and consisting of particles, exceedingly minute, cast off from the luminous surface," and rejects the idea of Descartes and others, that light is only a "mere quality."

The author next adverts to the origin of light, but which is the least luminous part of his essay. Descending to his mundane object, he considers, in his way, reflected, phosphoric, electric, and spontaneous light emitted by various minerals, animals, vegetables, and their combinations.

The luminosity of the sea, afterwards fully treated of, he says is caused by the presence of luminous insects, as the Cancer fúlgens, shining crab, &c.; and many instances of spontaneous light are evolved by chemical processes and combinations, under the action of heat, as the Chlorophane (chloros, green, phainō, to shine; gives out a beautiful applegreen light when placed on a heated iron; petalite (petalon, a thin plate; laminar fracture) rubelite (rubellus, reddish; colour), tungstate of lime, anatase, &c.

Many substances, according to Mr. Skrimshire, emit light on being brought within the circuit of an electric current, as alum, sugar, chalk, &c.

Some diamonds emit light in the dark, and especially, according to Boyle, if slightly heated, rubbed, or compressed. "Canton's phosphorus," not described by the author, "and the Bolognian stone, are phosphorescent when heated." Of this last curious substance, it has been said by naturalists, that

it retains the light of the sun for several hours after being exposed to it; but Mr. Murray takes no notice of this property, only that it becomes luminous, like many other substances, on being heated, independent of light. He also points. out the potato, decayed wood, several fish, as mackerel, whiting, &c., as emitting light; and of plants, the Tremélla meteórica, the Indian cress, and the subterranean Rhizamórpha (rhiza, root, morphe, form; resemblance) also evolve light in certain temperatures.

Percussion and friction are common sources of light, and many instances of luminous exhibitions occur in chemical practice, as well as in nature, which lead to the conclusion, that "the light in luminous animals is a consequence of, and has its being in, a peculiar organisation."

The luminous spherulæ of the glow-worm is a transparent sac or capsule, through which, as through a window, the light shines: it is quite distinct from chemical combustion and solar light. Of the latter the author gives a concise description, which may be best detailed in his own words.

"When a beam of solar light is intercepted by a prism, it unfolds a very beautiful and interesting spectacle. Seven colours are presented; and the bow of promise in the storm' affords a magnificent illustration of its phenomena. The colours thus unveiled are violet, indigo, blue, green, yellow, orange, and red; and they are refrangible in this order, the violet being the most easily refracted or bent, and the red with difficulty refracted. Agreeably to the doctrine of chromatics, taught us by Sir Isaac Newton, when all the colours are absorbed the object is black. Black, therefore, is the absence of all colour. On the other hand, when all the colours are returned or reflected, the object is white; when a particular colour is reflected, while the others are absorbed, the body appears of that particular tint." It is added, "that colour is the gift of light, numerous phenomena concur to assure us;" but he also avers that "there remain many circumstances extremely difficult to be accounted for; so that colours are to be considered accidental rather than essential properties of bodies." This part of his observations on light would, perhaps, have been clearer had he said that colours are the gift of form and position.

After some further disquisition on light and colours, in which a considerable share of sound philosophical knowledge is elicited, he comes to the examination of the light of the glow-worm.

Of luminous insects in this country, the Lampyris (lampō, to shine, pyr, fire) noctilùca (noctiluca, a candle) (fig. 58.),

or glow-worm, and the Scolopéndra eléctrica, are the most conspicuous and common. The Scolopendra is found in Huntingdonshire, and the Lampyris spléndida in the vicinity of Oswestry. The male glowworm yields light as well as the female, but much fainter. The eggs are also, in some degree, luminous. Their light, which they have power to extinguish at pleasure, proceeds from brilliant spots on the three last rings of the body, under the

tail; the luminous matter is a yellow substance, contained in vesicles; and when these vesicles are removed entire, they shine for some time afterwards; but if lacerated, they are extinguished. The shining substance, the author thinks, is not phosphoric, but monochromatic, and is a gummo-albuminous substance. He thinks, the only use of this insect's lamp is, either as a guide to its food, or as a sign to nightingales where to find their prey. No notice is taken of the old and most rational conjecture, that the light of the apterous female is only a signal to the coleopterous male. The propensity of the males flying towards light, in such numbers as sometimes to cover a table round the lighted candle, in an open room, is a presumptive proof of this last conjecture. Naturalists differ in opinion respecting the existence of the ignis fatuus; and those that admit its existence, differ as to its character; some insisting, as our author does, that it appears "as a glow of lambent flame," while others assert that it is only a luminous fly. It is probable that both phenomena have been seen.

On the Luminosity of the Sea. The light of the sea has been ascribed to various causes; by some to phosphorescence, the effect of animal decomposition; to the imbibition of solar light, analogous to the diamond, and to an electric effect induced by friction; while others have more plausibly assigned it to the presence of luminous animals, and of these the Medùsa pellucens, and hemisphérica, Límulus noctilùcus, &c. have been described." This phenomenon, so commonly seen every where, more especially in the Atlantic, under the bows of a ship, or in storms, has been settled long ago; and, no doubt, is caused by phosphorous mollusca floating on the surface of the water. The author claims the discovery, that this appearance on the sea is a presage of a storm; and, if future observations prove it to be so, it may be of the utmost

importance to mariners. On this point, his concluding paragraph deserves republication: "We dare scarcely speculate, touching the design of this singular distinction. This much we know, that Almighty Goodness has made nothing superfluous or in vain. The visitation of luminous animals seems connected with meteorological phenomena; and it would be interesting to ascertain, from different parts of the coast of Great Britain, what kind of luminous animals generally contribute to the effect."

On the Phenomenon of the Chameleon. This reptile is an inhabitant of intertropical climates; it belongs to the lizard family, and is particularly remarkable for the varying colours of its skin. Our author's experience of the nature of this animal has been directed to ascertain the cause of these changes, which, he says, "are depicted in such varying shades, that the magic of the necromancer's rod takes not the sense of vision more completely captive than do these ephemeral and sportive hues."

His convictions on this wonderful property are, that the changes are caused by the circulation of the blood of the reptile, and that increased temperature, either of the ambient air or of its own body, produces all the variations of the skin. And, as the passions of the human mind change the colour of the skin as well as the form of the features, and according to the rapidity of the flow of blood, so Mr. Murray thinks that the feelings of the chameleon may also, in some measure, produce analogous changes in the reflecting surface of the skin.

On the Ascent of the Spider into the Atmosphere.-Gossamer has been long noticed by both poets and naturalists. About the beginning of the last century, it was supposed to be condensed vapour. Geoffroy gave it as his opinion, that it was a web spun by the Acarus (tick) telàrius (tela, a web), on the north side of trees; and being from thence dispersed by the wind, covers the fields with those innumerable threads! It is now known to be produced by many different kinds of spiders, particularly the flying spiders. Our author has paid particular attention to the economy of these insects, and assures us that they have actually the power of projecting their threads to a considerable distance, and by such means transporting themselves from the ground to any elevation, or from the top of one elevation to another. But what is still more astonishing, he conceives that these threads are electric, or so actuated by that subtle element, that buoyancy is imparted, and the baseless shrouds of the aerial traveller are, with itself, projected aloft into the highest regions of the air!

There are but very few spiders, which, in crawling over uneven surfaces, do not leave behind them a thread, serving as a cable, or rather a line of suspension, lest they should fall, or be blown off from any eminence; consequently, the whole surface of the ground, throughout the summer months, is covered with their network; not only with webs of the ground spider, which may be called personal property, but from innumerable threads of vagabonds. This accumulation creates no wonder, because it is certain that these threads, however delicate, are at the same time durable. But that this tissue is constantly increasing, may be seen by following the plough for a short space: for no sooner has the team finished one land or ridge, but the fresh ground is quickly interlaced with threads, which glisten in the sunbeam. There is no accounting for this, except on the facts stated by the author, viz. that the air in fine weather is filled with the excursive threads of the impennous Arànea aeronaútica. The insect is often detected at the end of its thread, with its little arms extended, and balancing itself like a bird, and always proceeding before the wind. This direction of their flight always accounted for the connection between tree and tree, or hedge and hedge; moreover, the insect by its instinctive sagacity, in committing a coil of its thread to the wind, and taking its chance of a distant attachment, could then transport itself in safety. But the author has seen threads projected or propelled in a close room, where there could be no current of air to carry the same in any direct line; and so far the relation is most interesting.

Many curious experiments were made by the author, to prove that electricity, either positive or negative, was an agent in the movements of this spider, and the results far to estago blish his hypothesis. This opinion, however, is refuted by J. Blackwall, Esq. in Lin. Trans., vol. xv. part ii. p. 449. who proves that spiders have no power of propelling their webs, without assistance from the wind; and that the cobwebs seen floating in the air, are raised from the surface of the ground, by the action of air highly rarefied by a cloudless sun.

Mr. Murray also thinks that spiders are attracted by musical sounds; but it is more probable that they descend from ceilings, &c. towards an instrument from an impulse of fear, caused by the vibration of the air, than from any relish for melody. In this section of the book the writer has many pertinent remarks on the structure and economy of the insect creation: all showing how important it is to the other branches of animated nature, as affecting vegetation, and even man himself. Insects can, and actually do, change the features of the