solutions of Epsom and other salts, and found that in slight solu. tions it shone brighter: but that in strong solutions it became apparently extinguished, though it again revived by mixing more water, and reducing the solution to its proper debility; and thus by alternately adding fresh salt, and new supplies of water, he has sometimes revived the same light after ten extinctions. Great cold and heat are also found to extinguish it; yet a moderate heat ren. ders it more brilliant: it begins to be extinguished at 96°; and when the thermometer is raised to 100 it can be no more revived. It is however capable of being revived, after being frozen by frigorific mixtures.

It is therefore an anomalous fact, that the light of dead glowworms continues to augment in heated water, increased to 114 degrees.

Luminous appearance of the Sea.

FROM what has already been observed, this beautiful and bril liant phenomenon is not difficult to be accounted for in most cases: for the vast mass of the ocean contains in itself whatever has the greatest tendency to the production of such a phenomenon. It is the natural province of the greater number of those animals that secrete light from peculiar organs with which they are endowed for this purpose, of phloades, nereids, medusas, and luminous can. cers; it holds in its immense bosom, at all times, an enormous quantity of that kind of animal matter, (marine fishes) which is most disposed to throw forth its latent light, in an aggregate and visible form, during its first progress of decomposition; and unites the different circumstances which chiefly favour such an evolution; such, for instance, as a fluid menstruum, temperate warmth, and a solution of muriat of soda or common salt.

If then we see occasionally, in vegetable matter undergoing a slow decomposition, as in rotten wood, a certain portion of light poured forth in a visible form; if we see it issuing in a still greater degree from bones and shells that have undergone the process of calcination; if we see it still more freely at times, and under circumstances, thrown forth from the animal exuvia of church. yards, and adhering to the surface of the spot from which it issues, in like manner as the light scraped off from the scales of pieces of putrescent fishes, immersed in salt water, adheres to the knife or the fingers that are employed for this purpose; how much more easily may we expect to see it thrown forth, and in how much

larger quantities, from different parts of the ocean, under circum. stances that may favour its escape; often adhering to the sides of vessels, or of their oars as they are alternately raised from the water, and producing a long line, or an extended sheet, of wonderful brilliancy, not unfrequently variegated by every playfulness of colour.

It appears obvious, moreover, that it is not to one cause only, but to many, that such phænomena are to be ascribed, at different periods, and in different parts of the world. Linnæus inclined to confine it chiefly to vast flocks of the nereis tribe: but we have already observed, that even at sea, and among living animals, medusas, sapias, pennatulas, pyrosomas, and phloades equally concur while, on other occasions, the waves appear brilliantly illuminated, and through a very extensive range, without a trace of any living substance whatever, possessed of a luminous power; and can only acquire their light from the decomposition of dead animal matter. [Pantologia.

CHAP. IX.

SPONTANEOUS COMBUSTION.

In the preceding chapter we have confined our remarks to sub

stances which spontaneously emit light with little or no increase of sensible heat. In the present we shall have to notice other substances that spontaneously emit heat, and burn, either in conjunc tion with light, or, as very frequently happens, without any light whatever in the course of which we shall have to glance at some very remarkable and interesting effects, which to this hour have never been satisfactorily explained.

Spontaneous combustion, as a general fact, is well known; and the more common causes are too obvious to be enlarged upon; we need only refer to friction and its effects, to the heat produced by the slacking of lime when in contact with combustible matter, to the fermentation of hay, of dunghills, and of similar materials similarly disposed.

But besides these more common causes, experience has shown

that many vegetable substances, highly dried and heaped together, will heat, scorch, and at last burn into flame. Of these the most remarkable is a mixture of the expressed oil of the farinaceous seeds, as rape or linseed oil, with almost any other dry vegetable fibre, such as hemp, cotton, matting, &c. and still more, if also united with lamp-black, or any carbonaceous substance. These mixtures if kept for a time undisturbed, in close bundles, and in a warm temperature, even in small quantities, will often heat, and burn with a mouldering fire for some hours; and if air be admitted freely, will then burst into flame. To this without doubt may be attributed several accidental conflagrations in storehouses, and places where quantities of these substances are kept, as has been proved by direct experiments. The most important of these expe riments were made by Mr. George, and a committee of the Royal Academy at Petersburgh, in the year 1781, in consequence of the destruction, by fire, of a frigate in the harbour of Cronstadt; the conflagration of a large hemp magazine, in the same place, in the same year; and a slight fire on board another frigate, in the same port, in the following year.

These accidents led to a very strict examination of the subject, by the Russian government; when it came out, that at the time of the second accident, several parcels of matting, tied with packthread, in which the soot of burnt fir-wood had been mixed with oil, for painting the ship, had been lying some time on the floor of the cabin, whence the fire broke out. In consequence of which, the following experiments were made: forty pounds of fir. wood soot were soaked with about thirty-five pounds of hemp oil var. nish, and the whole was wrapped up in a mat, and put in a close cabin. In about sixteen hours it was observed to give out a smoke, which rapidly increased, and when the door was opened, and the air freely admitted, the whole burst into a flame. Three pounds of fir-black were mixed with five pounds of hemp-oil varnish, and the whole bound up in linen, and shut up in a chest. In sixteen hours it emitted a very nauseous putrid smell and steam; and two hours afterwards it was actually on fire, and burnt to ashes. In another experiment, the same occurrences took place, but not till the end of forty-one hours after the mixture had been made; and in these and many similar experiments, they all succeeded better, and kindled sooner on bright, than on rainy days. Chimney soot used instead of lamp-black did not answer, nor was any effect

produced, when oil of turpentine was substituted for the hemp of rape-oil. In general it was found, that the accension took place more readily with the coarser and more unctuous fir-black, than with the finer sorts; but the proportions of the black to the oil did not appear to be of any great moment. Sometimes, in wet weather, these mixtures only become hot for some hours, and then cooled again, without actually taking fire.

In all these cases the soot or black was from wood, and not coal. The presence of lamp-black, or any other dry carbonaceous matter, is not necessary however; for a spontaneous inflammation will take place in hemp or cotton, simply soaked in any of these expressed oils, when in considerable quantity, or under circumstances favourable to this process, as in very hot weather, or closely shut up. An accident of this sort happened at Gainsborough, in Lincolnshire, in July, 1794, with a bale of yarn of 120lb., accidentally soaked in rape-oil; which, after remaining in a warehouse for several days, began to smoke, to emit a most nauseous smell, and finally to burst out in a most violent flame. A similar accident, with a very small quantity of the materials, happened at Bombay. A bottle of linseed oil had been left standing on a chest; this had been thrown down by accident in the night, the oil ran into a chest which contained some coarse cotton cloth, and in the morning the cloth was found scorching hot, and reduced nearly to tinder, and the wood of the chest charred on the inside. On subsequent trial, a piece of the same cloth was soaked in oil, shut up in a box, and in no longer time than three hours it was found scorching hot, and on opening the cloth it burst into fire. Similar to this is the spontaneous combustion of wool, or woollen yarn, which has occasionally happened when large quantities have been kept, heaped up in rooms little aired, and in hot weather. The oil with which wool is dressed, which is generally rape-oil, appears the chief agent in this combustion. Even high dried, oily, or farinaceous matter of any kind, will alone take fire, when placed in circumstances very favourable to this process. Rye flour roasted till half parched, and of the colour of coffee, and wrapped up in a linen cloth, has been found to heat violently, and to destroy the cloth. Wheat flour, when heated in large quantities, and highly dried, has been known to take fire in hot weather, causing accidents in granaries and bakers' shops. An accident of this kind is related by Count Morrozzo, in the Memoirs

of the Turin Academy, to have happened at a flour warehouse at Turin, containing about three hundred sacks of flour. It began by a violent explosion, on a lamp being brought into the ware. house, and the whole was soon after in flames. Charcoal alone also has been known to take fire in powder.mills, when quantities of it in powder have been kept for some time closely packed. Another, and totally different species of spontaneous combustion, is that which occurs during the oxygenation or vitriolization of pyrites, or sulphurets of iron, copper, &c.

A most curious, and, if not well authenticated, a scarcely credible species of spontaneous inflammation, is that in a few rare instances, known to occur in the human body. It is not quite certain indeed, whether the first inflammation has been quite spontaneous, or caused by the approach of a lighted substance; but in these melancholy accidents, the body of the unfortunate sufferers has been brought to a state of such high combustibility, that the flame once kindled, has gone on without other fuel, to the entire destruction of every part, (the bones and extremities excepted) and, as it appears, has been attended with actual flame, of a lam. bent faint light. This change is the more remarkable, as the human body, in all its usual states, both of health and disease, is scarcely at all of itself combustible, and cannot be reduced to ashes without the assistance of a very large pile of faggots, or other fuel; as universal experience, in the very ancient mode of sepul. ture, and the history of martyrdoms, abundantly shews. Cases of this human combustion on record, have occurred in different countries. Two of them, well authenticated, are recorded in the Philosophical Transactions, and occurred in England; and a few others in Italy, France, and elsewhere. In all but one, the sub. jects of them have been females rather advanced in life, of indolent habits, and apparently much addicted to spirituous liquors.

The accident has generally been detected by the penetrating fetid smell of burning and sooty films, which have spread to a great distance; and the sufferers have in every instance been discovered dead, and with the body more or less completely burnt up, leaving in the burnt parts only an oily, crumbly, sooty, and extremely fetid matter. Another circumstance in which these cases all agree, is the comparative weakness of the heat produced by this combus tion, notwithstanding the very complete disorganization of the body itself, so that the furniture of the room, wooden chairs, &c.