It might be objected to this view of the final causes, that, although the larger or true fishes, and the insects of the sea, are provided with organs of vision, a very large part of the maritime creation has none, and could not therefore profit by the light. Assuredly there is no appearance of eyes, nor indeed of organs of any sense at all, in numerous genera ; and, in particular, of those commonly called worms or vermes, whether these are naked or the inhabi tants of shells. Nor have we any doubt that there are ma ny animals in the sea which have no use for light nor any concern with it. Yet, that some of these imperfect ani mals have the means of seeing or feeling light, if we may choose to term it so, without appearing to be furnished with any special provision for that purpose, seems fully proved by the experiments of the observer above mentioned. He convinced himself by many trials, that some of the Beroes and the Medusx, when confined in a glass at night, were at tracted by the light of a candle. In one large Beroe this was so remarkable, that the animal could be conducted by the light in a circular direction round the glass for any length of time, while its motions could be reversed by changing that of the candle. In this case it always presented the anterior extremity, yet there is no organ of any kind situ ated there, any more than in the Medusa. In fact, this genus, like the Medusa, seems to possess no organs of any kind but the stomach and the swimming machinery. It was impossible to try this experiment on the smaller tribes with any chance of success, so that these trials were necessarily limited to a few species. Yet it is highly pro bable that a similar sense is widely diffused among the ana logous animals, since all have the same habits and wants, and that they all affect the light of day, is most evident from their invariably swimming near the surface, except when atmospheric changes drive them below. In a phy siological view, we need have no objections to the exist ence of this power. The eye is an optical machine, in tended to produce an image ; but light alone may be per ceived by an arrangement of nerves, similar to that of the retina, so that the perception of light, which is all that is here contended for, may as well belong to the Medusa and Beroes as to any other animals provided with a ner vous system.
Phosnhorescnce of Vegetables.
We know not of any authentic instance of a luminous appearance arising from living vegetables which can be referred to phosphorescence. It is true that some au thors have seen, or imagined, that the tuberose, and one or two other flowers, give out a light, under peculiar cir cumstances, at the moment of their expansion, which some have referred to this cause, and which others have attri buted to electricity. But the instances of this occurrence are as yet so rare, that, although we have no reason to dis trust the accuracy of the reporters, we are in no condition to reason on this phenomenon ; if, indeed, it belongs to the division of luminous appearance under view.
In wood, under certain states of decay, however, this phenomenon is known to every schoolboy. Yet neither the peculiar circumstances requisite for its production, nor the cause of the light, have been satisfactorily ascer tained. Neither is it well known to how maw kinds of wood it is limited, or whether, if the same hind of decay can be produced, it may not occur in 5..;1. In the soft
woods, such as willow, hazel, and birch, it appears, at any rate, to be most frequent. It has been observed in the sugarcane. When wood is them luminous on decay, it is spongy and somewhat moist, being also very tender, of a white colour, and often 9,ained with green and blue tints, that seem to be the result of some process of fermentation sin tilar to that, which, in so many vegetables, produces in digo. This effect is, however, transitory, and it appears n '7 to be limited to some very particular stage of the progress of decay, as it seldom lasts above two or three days. M. Dessaignes considers that humidity and the contact of air are both necessary, and that the effect does not take place, unless the temperature is 8° or 10° of the centigrade ther mometer. The light is extremely pale and gentle, with a slight bluish tinge, and is not very unlike to that which is given out by the dead fish in their luminous stage. It is accompanied by no smell, or any heat, and the cause has as yet eluded the investigations of chemists. Yet the same author thinks that a chemical combination is going on, analogous to that by which lime unites to water, in which light is, in the same manner, generated.
As analogous to this, we must consider the light that is sometimes yielded by peat, which we have observed in the Highlands of Scotland, but which has not been notic ed by authors, except by Dr. Macculloch, in his account of the Western Islands. This also appears to be a transi tory light ; and, from that cause, as well as from its mi nuteness in size, and its feebleness, it may easily escape obseri ation. - We have only found it in that kind of fine and smooth naked peat so common in wet mountains, which occupies these deep channels and cuts, well known to sportsmen as well as mountaineers, for the impedi ments they produce in wandering over such regions. It is not even visible at the ordinary distance of the eye from the ground, but may be seen by close inspection. We have never found it otherwise than in small spots, not ex ceeding the head of a pin in size, and of a dark blue co lour, resembling that of burning sulphur. At first we had imagined these lights were produced by some minute lu minous animal, and were only convinced of our error by a careful microscopic examination. Respecting the cause we have no conjectures to offer.
These cases, according to M. Dessaignes' theory, must both equally proceed from a species of combustion, in which water and carbonic acid are formed. Wood loses half its weight during the process ; and, according to him, though not at first extinguished in airs that contain no oxygen, it at length ceases. It is also destroyed by boil ing water, and ceases at the freezing temperature.
Miscellaneous Sources of Phosphoresence.
We have been obliged to adopt this division for the pur pose of including some luminous appearances that do not well fall under any of the other heads, but which, for want of more knowledge, have been classed under this sweeping term. In all, the causes are as obscure as in any of the in stances already pointed out, and more inexplicable they need not be.