ng entire within. At other times wood thus incrusted is eroded by the matter which covers it, baving something acrimonious in its substance. We may add to these, clusters of the twigs of shrubs, and small wood, which we find flakes of, incrusted with sparry or calcareous matter, in many places; parts of which are totally changed into that matter, whilst others are only enveloped with it. Bones of Animals-We see by daily experience, that the human skeleton moulders to dust in a very few years, when buried in mould: so it does even in vaults, where the coffins are kept dry. In the first case, the moisture and salts of the earth divide and dissolve the texture of the bones; in the latter, those of the air, which gradually insinuate themselves into them, and at length destroy them. How long a skeleton whose bones are well dried and prepared, being totally deprived of its medullary substance, will last, as they are now ordered for anatomical purposes, is unknown; but it may be reasonably conjectured, that they will undergo the fate of the softer kinds of wood, such as beech, which grows rotten in no great number of years; because their internal substance is spongy and cellular, and their crust very thin, except about the middle of the bones of the arms and thigh. The same destruction would happen if bodies were deposited in a sandy soil; because water finds its way either by dripping downwards, or by springs underneath. But human skeletons have been found entire within a rock, where neither moisture nor air could get at them. Mr. Minors, an eminent surgeon and anatomist of the Middlesex hospital, when he was in the army at Gibraltar, saw an entire skeleton, standing upright, in a dry rock, part of which had been blown up with gunpowder, in carrying on some works in the fortifications, which left the skeleton quite exposed. Indeed, the bones of elephants have been found in Shepey island, but much destroyed; their size and substance being so considerable, as to resist for a long time that decay which those of the human could not withstand. To these may be added the horns of large animals, as the elk, and others, which have been found in bogs, preserved as the bog-oak, &c. above-mentioned. Teeth and Palates of Fishes and other Animals.-These are of so hard and firm a texture, as to suffer no great change, wherever found; for no erosion appears in them, their enamel and its polish being entirely preserved; yet sometimes their roots will be found changed, especially in the yellow ones, having no enamel to guard them in their roots. Parts of Vegetables.-The leaves of plants, whose fibres are firm and dry, will endure for a long time; but those of a succulent nature never can, as they putrify very soon. We see the leaves of ferns of several kinds, polypodium, trichomanes, and other capillary plants, with nodules of stone formed about them; flags, reeds, rushes, equisetum, and many such, of a firm texture, are found in slate and stone; and even the iuli of trees are said to have been found fossil as their leaves. Seeds and Fruits.-All seeds and the stones of fruits, having a firm texture, are also capable of being strongly impregnated with stony and pyritical matter; and doubtless the smaller seeds, if carefully looked for, might be found fossil, as well as these now produced, viz. such as have a firmness in the covering; but being small, and mixed with the dirt, sand, &c. probably is the reason of their being overlooked. Fruits of various kinds are found petrified; but this is only in their green state, when they are hard enough to endure till they are impregnated with stony or mineral particles. The rudiments of fruits, when once well formed, and a little advanced, are firm and acid: and the more remote they are from maturity, the more secure from putrefaction; and their acid juice is no small help to their preservation from growing soon rotten. But when the fruit advances in growth, the texture becomes gradually more lax; the acid juices are now beginning to be replaced by saccharine or others more soft; the fibres are driven farther asunder, and they now arrive at their most ripe state: and the utmost maturity of fruits is the next step to putrefaction. Hence they are destroyed before stony or other particles can have time enough to impregnate them : and this is exactly the case with the flesh of animals of every kind. The husks and hard calyces of fruits, as well as their stones, are also susceptible of petrifaction. If these fruits, now produced, are antediluvian, one would be apt to imagine they in some measure point out, with Dr. Woodward, the time of year in which the deluge began; which he thinks was in May: and yet this very opinion is liable to some objections; because though fruits capable of being petrified, from their green state, may be pretty well formed in May here, as well as in the same latitude elsewhere, in favour of this opinion; yet the stones of fruits are found fossil so perfect, as to make one imagine they were very ripe when deposited in the places where they are discovered; which would induce us to think the deluge happened nearer autumn, unless we could think them the productions of more southern latitudes, where perhaps their fruits are brought to perfection before ours are well formed. The following observation of Dr. Mason, Woodwardian professor, is well worth notice. It regards the impressions of fishes upon slate. Now there are several kinds of slate, which have such impressions on them: in some there remains only the bare impression, without any part of the fish; in others the scales only, but retaining the entire form of the animal; and in others no part adheres to the slate but the skeleton, or part of it, most commonly the spine. He says that he always observed, that the bones are never seen but on the grey or blue slate, or their impressions; and that the scales or skin are to be found only on the black stone or slate; which makes him conjecture, that something erosive in the grey slate destroys every part but the bony system; but that the black, being of a more soft and unctuous nature, preserves the scales, and often the very skin. The catalogue of these fossil-fruits, &c. is as follows. Fig. 1, 3, pl. 6, seem to be figs, petrified when hard and green.-Fig. 2 appears to be a myrobalan, distinguished from the other species of that name by its round figure; and is called the emblica myrobalan. It is nearly destroyed by the pyritical matter, and will not long remain whole.-Fig. 4 seems to be a species of phaseolus, one of those especially distinguished by the fruits. Fructibus splendentibus nigris.-Fig. 5, another phaseolus.-Fig. 7, another. See fig. 4.-Fig. 8, semen cucurbitæ, a large species of American gourd.-Fig. 9, coffee-berries.-Fig. 10, 11, two species of beans, very apparent,-Fig. 12, unknown. This however appears to be a fruit, with the calyx running up, and embracing it, in its hard green state; being somewhat compressed on the upper part, as it lay confined in the earth.-Fig. 13, perhaps a species of staphylodendron.-Fig. 14, a compressed pod of the Arachidna, or underground-pea.-Fig. 15 is evidently an acorn. We have of this species here, and in America also.-Fig. 16, an exotic fruit, like a small melon; but uncertain. Fig. 17 seems to be a fungoides of a very pretty kind.-Fig. 18, probably a seed of a species of water melon. -Fig. 19, seems a small plumb-stone.-Fig. 20, unknown. The calyx seems to run up and embrace this fruit towards the apex.-Fig. 21, unknown. This resembles an American seed, which he had.-Fig. 22, a lachryma Jobi?-Fig. 23, a cherry-stone. Fig. 24. If this be an euonymus, it is not so far advanced as to form the seeds; and is therefore to be considered only in its progress from the flower towards seeding.-Fig. 25, a berry of the sapindus, or soap-tree, of America, being not at all deformed, only having a little lump of pyrites on it: but there is another quite free.-Fig. 26, huræ germen. This is undoubtedly the young sand-box, or fruit of the hura, so well known for its beautiful form to the curious, who collect specimens of natural history; and seems to show the time of the deluge.-Fig. 27, is certainly the stone of an eastern mango; such as comes over to us pickled, and the stone being opened on one side, is generally stuffed with spices.-Fig. 28, is a large species of euonymus, perhaps of Clusius.-Fig. 29 seems to be a milleped, or woodlouse.-Fig. 30, a small long bean, like our horse-bean; but longer than any we have in England.-Fig. 31, unknown.-Fig. 32, a species of horse-chestnut from America.— Fig. 33, the external husk of the fruit of the sapindus, or soap-tree.-Fig. 34, either an olive, or the yellow myrobalan; but probably the latter.-Fig. 35, seems a small palma-coco.-Fig. 36, 37, 38, 39, unknown. The reason of the four last being not to be distinguished is, that they seem to be the buds of their several species, before they were perfectly formed. So that while some of the antediJuvian productions are mature, others appear to be premature; and consequently one would be inclined to think them the inhabitants of places of different latitudes.-Fig. 40, a species of foreign walnut, injured and compressed.-Fig. 41, a plumb-stone.-Fig. 42, the claw of an American crab; which, being on the opposite side of the mass containing the body, could not come in view with it at the same tiine.—Fig. 43, the body of the crab, with other parts, appearing through the stony matter that invelopes it, which appears to be an induration of yellow clay.-Fig. 44 seems a long American phaseclus. Part of the petrified husk is upon it.-Fig. 45, an American echinite of the flat kind, ⚫ much resembling that species which Rumphius calls echinus sulcatus primus.-Fig. 46, has all the characteristics of an ear of corn, or some species of grass, of which there are many. Fig. a, a manifest species of pediculus marinus crumped up.-b, a seed-vessel, given him by Mr. Da Costa, found in a clay-pit in Staffordshire. c, Cocculus Indicus. LII. Observations on the Comet that appeared in Sept. and Oct. 1757, made at the Royal Observatory by Ja. Bradley, D.D., F.R. S. p. 408. When Dr. B. first discovered this comet, it appeared to the naked eye like a dull star of the 5th or 6th magnitude; but viewing it through a 7-foot telescope, he could perceive a small nucleus, surrounded as usual with a nebulous atmosphere, and a short tail extended in a direction opposite to the sun. By comparing its situation with some near stars, Dr. B. collected, that the comet's right ascension was 89° 29′ 10", and its declination 35° 0′ 20′′ north. In like manner he collected the places of the comet on a great many following days, till the 19th of October, on the morning of which day it appeared so faint, that he could not observe its place. Its elongation from the sun was then but about 20 degrees; and from that day it became always less; which is the principal reason why it was invisible at the time when in its perihelion. The elongation will indeed soon become greater, and yet it is probable that we shall not be able to see the comet again; because its real distance from the sun will be greater than it was when he first saw it, and it will be also 4 times further from us than it was at that time. The comet kept nearly at the same distance from the earth for ten or 12 days together after he first saw it; but its brightness gradually increased then, because it was going nearer to the sun. Afterwards, when its distance from the earth increased, though it continued to approach the sun, yet its lustre never much exceeded that of stars of the 2d magnitude, and the tail was scarcely to be discerned by the naked eye. Supposing the trajectory of this comet to be parabolic, Dr. B. collected from the foregoing observations, that its motion round the sun is direct, and that it was in its perihelion October the 21st, at 7h 55m mean or equated time at Greenwich. That the inclination of the plane of its trajectory to the ecliptic is 12° 50′ 20′′; the place of the descending node 8 4° 12′ 50"; the place of the perihelion 2° 58′ 0"; the distance of the perihelion from the descending node 88° 45' 10"; the logarithm of the perihelion distance 9.528328; the logarithm of the diurnal motion 0.667636. From these elements, which are adapted to Dr. Halley's general Table for the Motion of Comets in parabolic Orbits, Dr. B. computed the places of this comet for the respective times of the foregoing observations, as in the following table, which contains likewise the longitudes and latitudes deduced from the observed right ascensions and declinations, and also the differences between the computed and observed places. These differences, (no where exceeding 40′′) show, that the elements here set down will be sufficient to enable future astronomers to distinguish this comet on another return; but as they do not correspond with the elements of the orbit of any other comet hitherto taken notice of, we cannot determine at present its period. -22 -40 A LIII. The Resolution of a General Proposition for Determining the Horary Alteration of the Position of the Terrestrial Equator, from the Attraction of the Sun and Moon: with some Remarks on the Solutions given by Other Authors to that Difficult and Important Problem. By Mr. Tho. Simpson, F.R. S. p. 416. Since the time that Dr. Bradley published his observations and discoveries concerning the inequalities of the precession of the equinox, and of the obliquity of the ecliptic, depending on the position of the lunar nodes, mathematicians in different parts of Europe have set themselves diligently to compute, from physical principles, the effects produced by the sun and moon, in the position of the terrestrial equator; and to examine whether these effects do really correspond with the observations. Two papers on this subject have already appeared in the Phil. Trans.; in which the authors have shown evident marks of skill and penetration. There is nevertheless one part of the subject that seems to have been passed over without a due degree of attention, as well by both those gentlemen, as by Sir Isaac Newton himself. This part, which on account of physical difficulties, is indeed somewhat slippery and perplexing, is the principal subject of this essay. GENERAL PROP. Supposing a homogeneous sphere OABCD (fig. 1) revolving miformly about its centre, to be acted on at the extremity A of the radius oa, in a direction AL perpendicular to the plane of the equator ABCD, and parallel to the axis of rotation pp, by a given force, tending to generate a new motion of rotation at right angles to the former: it is proposed to determine the change that will arise in the direction of the rotation, in consequence of the said force. Let F denote the given force, by which the motion about the axis pp is disturbed, supposingƒto represent the centrifugal force of a small particle of matter in the circumference of the equator, arising from the sphere's rotation; and let the whole number of such particles, or the content of the sphere, be denoted by c: let also the momentum of NM |
