(Table continued.) Substances submitted to Desiccation at the Tem perature of Boiling Water, their original Weight Coal of Loebejun, in the circle of the Saale in Prussia, with pulverulent coke, Piciform coal of Planitz, kingdom of Saxony, with con- Coal of Pottschapel, near Dresden, with intumesced coke, Glance coal of Lischwitz, near Jena, in Saxony, Coal of the country of Waldenburg, Lower Silesia, with Weight retain ed after Desiccation. 99. 94.3 94.4 98.3 95.95 94.8 94.9 95.5 97.8 Another variety of the same, with pulverulent coke, 97.1 Coal of the country of Waldenburg, passing from coal with 98.5 97.1 Coal of the country of Waldenburg, with pulverulent coke, 96.4 Coal of Upper Silesia, with conglutinated coke, 95.9 Coal of the neighbourhood of Beuthen, Upper Silesia, with Coal of the country of Saarbruck, with intumesced coke, Coal of Eschweiler, country of Aix-la-Chapelle, with intumesced coke, Coal of Eschweiler, another bed, with intumesced coke, Coal of Wellesweiler, country of Saarbruck, with intumesced coke, 99.1 97.85 Coal of the country of Waldenburg, Lower Silesia, with The loss of weight indicated by this table, whatever differences it may present, does not appear to have any relation to the properties of the varieties of coal, and in general of the matters subjected to experiment. The greatest loss was experienced by the fossil wood and by the coal with conglutinated coke having but a small proportion of charcoal. The former substance losses 19.8, and the latter 6 per cent. The more the quantity of charcoal increases, the smaller does the loss of weight become. M. Karsten, however, was surprised to see that a coal analogous to anthracite, and anthracite itself, experienced a considerable loss (from 5 to 6 per cent.), which would not have been presumed from their hardness and semimetallic lustre. In general, the lightness, that is to say the porous and loose state of a body, does not appear to have any influence upon this loss of weight, or at least it does not always exert an influence upon it; for if it did so, mineral charcoal, which, of all the substances submitted to trial, is the lightest and loosest, perhaps, without excepting even wood charcoal, would have experienced the greatest loss. The charcoal of mineral wood, however, does not lose more than 1, while the hard and shining anthracite of Rhode Island loses upwards of 5 per cent. On the other hand, graphite, rendered very loose by bruising and pulverization, preserves its weight unaltered. Are the loss of weight which charcoals experience, and their subsequent increase on exposure to the atmosphere, owing to the emission and absorption of atmospheric air and humidity, or of humidity only? The author has not entered upon this inquiry; but he thinks, that, with the view of elucidating the cause of the differences which are observed in the manner in which mineral combustibles comport themselves, it would be interesting to try them thus at the moment of their being taken from the mine, and particularly those which in the open air increase consider. ably in weight. With regard to such coals as experience a very considerable diminution of weight, on being dried at the temperature of boiling water, their produce in coke by carbonization ought to be very small, and not to agree with the results of chemical analysis, if, as is commonly done, coals dried in the air be employed in the carbonization, and in the chemical analysis, coals dried at the temperature of boiling water. (To be continued.) 297) Considerations regarding the shining of the Eyes of the Cat, and several other Animals. By M. BENEDICT PREVOST. EVERY body knows that the eyes of the cat shine in the dark. Our domestic cats afford us so frequent opportunities of observing this phenomenon, that it seems peculiar to them; but there are several other animals which equally present it, and I have seen it in the dog, the sheep, the cow, the horse, the polecat, and even in several serpents, and in some insects, among others in the species of sphynx commonly known by the name of the Death's-head Moth. Buffon says that "the eyes of the cat shine in the dark somewhat like diamonds, which throw out, during the night, the light with which they were in a manner impregnated during the day." Valmont de Bomare says, that "the pupil of the cat is during the night still deeply imbued with the light of the day," and some lines lower he adds, " the eyes of the cat are during the night so imbued with light, that they then appear very shining and luminous." Spallanzani says that "the eyes of cats, polecats, and several other animals, shine in the dark like two small tapers, and that this light is phosphoric." M. Dessaignes, in his memoir on phosphorescence, which was crowned by the Institute on the 5th April 1809, says that "the eyes of certain animals have the faculty of inflaming, and of appearing like a fire in the dark. Thus the most eminent naturalists and philosophers are of one mind with the vulgar in regard to this fact, that the eyes of cats and some other animals shine in the dark with a light which is peculiar to them, or with which they have been impregnated during the day. I myself, also, was long in the habit of acquiescing in this opinion, taking the matter partly upon the authority of others, and partly observing the phenomenon for myself in the vague way in which every person sometimes observes things, and men of science as well as others; which would not, however, be productive of great inconveniences, were not more importance attached to the citing such observations than to the making them. Every body," says Montaigne," is subject to say foolish things; the misfortune is to say them curiously." 66 I am quite certain, that neither Buffon, nor Spallanzani, nor M. Dessaignes, ever observed on purpose the shining of the eyes of the cat, and that they never saw this phenomenon otherwise than cursorily, as one sees when he does not attend to a thing, or when one only partially attends to it; otherwise, they would immediately have perceived that the eyes of cats never shine in intense darkness, and that it is sufficient for them to shine, that too great a light does not prevent the pupil of the animal from dilating much; that, in reality, the phenomenon is only sensible to the observer, when his eye receives little light from surrounding objects. The case, then, is the same with the eye which shines, as with the light which the pictures of a panorama reflect, and which appears to have all the intensity of that of the objects which they represent, although much inferior to it. The less light the eye of the observer receives, the more is it sensible to that which the eye of the cat projects, and the less need has the latter of receiving any; it must receive more to produce an equal effect, if the former be situated in a lighter place. These are the conditions of the phenomenon. They appear to me to reduce this pretended phosphorescence to light reflected by a shining object. I shall give two examples, which I select from among the best adapted to render me understood. 1st, In a long and narrow passage, closed on all sides excepting the entrance, from which, during a very dark night, there could come but little light, I saw the eyes of a cat shine. They projected strongly upon the dark ground of a sort of deep nich, which made them appear like burning coals. The light which the eyes of the cat then received, and that which they sent back to me, was without doubt very weak; but to balance this, mine not being affected by any other light, would necessarily be very sensible to it. It was from a similar reason, that I once thought I saw from my bed something which shone like a star of second or third magnitude. It was nothing, however, but the back of a chair not very well smoothed, which reflected some rays of the moon; but having at the time my head almost entirely enveloped in my covering, and my eyes receiving no other light, these rays produced so much the more effect upon my retina, that they arrived the more isolated at it. 2d, In the other example which I have to adduce, the circumstances were in some measure the reverse. It was in a room where the sun shone, but the head of the cat was turned toward one of the corners, and I looked at it myself in such a manner as not to receive either the direct rays of the sun, or the light directly reflected. Here the eye of the animal received much more light than in the other example, and transmitted more to me, but my eyes receiving more light from another direction, and being on this account less sensible to it, the eyes of the cat did not appear so shining. Valmont de Bomare, in the article Chat of his Dictionary, (the edition in 15 vols.), says, after what we have already quoted, "it seems that the lustre, the splendour, which is observed in the day time in the eyes of the cat, comes from the shining part of the retina, at the place where it surrounds the optic nerve." This does not agree very well with what precedes; for in full day-light the retina of the cat is not visible, and if he means to speak of the lustre that is visible in a weak light, it is certainly of the same nature as that which is observed in darkness, and which Valmont de Bomare attributes to the imbibing-of the light of day. Nor does this author speak here from his own observation: what he says of the eyes of the cat is taken almost word for word from Buffon's works, and from the first edition of the Encyclopedie. We also find in the Geneva edition of 39 vols. 4to, article Chat, the following words: "It appears that the lustre, the shining, the splendour, which are observed in the eyes of the cat, come from a sort of velvet, which lines the bottom of the eye, or from the shining of the retina at the place where it surrounds the optic nerve." The phenomenon can be bè imitated with all its peculiarities, by placing bits of tinsel under suitable circumstances, or by other similar means. It is not therefore necessary to have recourse to phosphorescence for an explanation of it. It is certain enough, that a great number of substances become luminous in the dark, after having been exposed some moments to the light of the sun, or only to the ordinary day-light, or to the light of a lamp, or of the moon. But it is not probable that the eyes of the cat are of this class; for, like those of other animals, they are filled with various humours; and there results from M. |