Corresponding appearances took place when the ani mal was heated to similar temperatures in sand, or when ever moisture was not present ; except that in these cases the phosphorescence ceased at lower temperatures, as invariably happens whenever the luminous matter be comes dry. The same results were obtained from dead glow-worms, provided they had neither been dried up nor exposed to a greater heat than 45° or 50°. The rays of the sun, concentrated by a lens, produce the same effect as heat, and excite the phosphorescence immediately. If, on the other hand, a glow-worm is exposed to cold when in a luminous state, the light diminishes, and is extin guished as soon as the temperature has fallen below 10°. At 0° the insect dies ; but even then a heat of 25° will make the light re-appear. If it is killed by cutting off the head, or if the luminous part is cut off, the light ceases in about five minutes ; but after a short time it begins again to recover, and the light may then be main tained or re-produced for two or three days by the appli cation of heat. The insect that dies a natural death pre serves, in the same manner, a feeble phosphorescence for two or three days.
It had been remarked by former observers, that when a glow-worm, in the act of shining, was plunged into water, he phosphorescence ceased in a few minutes if it was alive, and in a hour or two if dead. M. Macaire con siders this to be a mere case of temperature, similar to these above mentioned. But if it is placed in alcohol, it is extinguished in two minutes,and the light cannot again be restored by heat. In the same way it is extinguished by the mineral acids, and that in proportion to their strength.
When this insect was placed in a receiver, and the air exhausted, it died, and of course swelled, so as sometimes to burst. No light could then be excited by the applica tion of heat, but, on letting in air, it immediately appear ed ; while these results were invariable in a great num ber of experiments. If the insect was introduced while in a luminous state, and the air exhausted gradually, the light was diminished in proportion, until it was totally ex tinguished. On letting the air again in it is restored ; and this experiment may be repeated with the same results many times in succession on the same insect.
Both in oxygen and in azote, the light appeared to be in• creased ; but the insect seemed to suffer inconvenience, and it was soon extinguished. In chlorine it died imme diately, with the loss of its light ; but on applying heat the light re-appeared, not however as before, but of a red colour, which also soon ceases. Hydrogen, carbonic acid, nitrous gas, with carburetted and sulphuretted hydrogen, extinguish the light quickly, and it is not in any of these cases restored by heat. It will be seen how these expe riments stand when compared with those of former ob servers ; and, as far as we can judge, from the manner in which this communication is drawn up, we should feel no hesitation in giving superior credence on all disputed points to M. Macaire's experiments.
No effects were produced by electricity, in whatever mode it was applied. But the effect of galvanism was to
excite the luminous action in the living animal, while it also ceased when the circuit was interrupted. The same effects were produced on the dead insect, and even on the luminous part of the body when separated ; and that hap pened even where no effect was produced by ordinary electricity. But in the vacuum, galvanism was ineffectual, and the light could not be renewed by it.
M. Macaire found that the luminous matter itself, when separated, was translucent and yellowish, that it became dark on drying, and appeared to consist of grains having an organic structure. Its specific gravity was somewhat greater than that of water. Exposed to the effects of dry ness and moisture, it gave the same results as in for mer experiments, and was also excited by heating as far i as 42° of Reaumur, when it was extinguished. It also to shine in vacuo, and is re-excited by the ad mission of air ; in other respects being affected by the different gases as it is when in the animal. When heated before the fire it ceases to shine, and when it is burnt, gives the smell of burnt horn, with a slight trace of ammonia. The mineral acids dissolve it when warm, and it commu nicates a bluish-green colour to the sulphuric ; but on saturating the acid with an alkali, no light is re-produced. It is not soluble in oils, either hot or cold; but ceases to shine, and, as is supposed, from the exclusion of air. Ether and alcohol render it white and opakc, and destroy the phosphorescence. Pure potash dissolves it, and acquires a light orange colour ; and saturation with an acid does not restore it. It is also destroyed by corrosive suhlimate, and other metallic salts. So far from being soluble in boiling water, it appears to acquire from it a greater de gree of consistence.
M. Maeairc concludes, strangely enough, as it appears to us, by determining that this luminous matter is chiefly composed of albumen, With respect to the use or design of this provision, it seems fully as obscure as the cause. It has been sup posed, indeed, (and the poets have made use of the thought,) that the female glow-worm made the signal to the other sex. But the male is also provided with it, and in the other luminous flies both sexes have the property alike. It has been thought a mode of defence ; but surely it is much more likely to be the reverse. So at least thought the author of the well known fable of the nightingale and the glow-worm. That it should assist the animal in pur suing its prey, or in avoiding injuries, is very possible ; but we fear that we must still confess our ignorance of the real designs of this, as well as of the ten thousand va rities in the forms and properties of the animal creation, which almost seem to us as if they were meant to show the exhaustless resources of nature, the wantonness, we might almost say, which she displays in the means of pro curing happiness to myriads of different animals, when, for aught we can conjecture to the contrary, a very few would have served the same purposes.