quence of which, any exertion may be beft carried on by a given elafticity, quite to the middle of the nail. The hoof of the fore-foot of a horfe is of the fame conftruction; which produces an elasticity continued from the quarters to the point of the toe. That point is the fulcrum of the fpring when molt violently exerted, as when a horfe is gallopping in full fpeed, or when drawing the greatest weight. The toe of the fore-foot is naturally therefore the hardest part; that it may be best enabled to refift the violent concuffions to which it is continually subject, from encountering hard and uneven fubftances. The fides of the wall are thinner towards the heels, to give room for the free motion of the flexor tendon, when that part of it which unites itfelf to the foot-bone is forced downwards, by the violent preffure of the toe against the ground; at which time the flexor tendon of the foot-bone is preffed down by the coronary bone and nut bone. The nut bone is interpofed between the flexor tendon and the other bones, to remove the infertion of the tendon further from the centre of motion, having a polished furface both towards the bones and towards the tendon. When the hoof is in fuch a flate as not to impede the action of the tendon upon the bones, it is the eafy play of thefe parts which produces that fpring to the foot, fo neceflary to the exertions of the horfe, and to the entertainment of the rider, when the horfe is required" aut molles glomerare gradus, aut feciere gyros." P. 3. There are feveral judicious obfervations on the modes of preferving the hoof, and on the treatment of its difeafes. "In refpect to hoof-bound horfes, I have frequently found that the wall on the infide of the foot is by no means fo ftrong as that on the outfide. The preffure on the inner fide is alfo in general the greateft, as appears from the more rapid wear of the inner fide of each hoe. Where horfes have the wall on the outfide very ftrong by nature, the infide quarter yields the moft to the preffure, which occafions the foot to have a tendency to turn out. To remedy this, I have ufually cut the bottom of the outfide wall more than the other, and raped the outfide quarter only, and have, in general, found this to be the best method. "I was however completely foiled in one inftance, which was the only time I have been tempted to try a different kind of fhoe from that which I fhall here recommend: having generally found that fhoes made in any particular way, for the fake of favouring this weak part, have been of little or no avail. The inftance in which I was difappointed is, that of a horfe kept entirely for the riding-houfe, and which is confequently almoft daily under my own infpection. This horfe has very strong feet, one of which was fmaller than the other, with the toe turning out, and the frog almost wafted. The bars of this foot, before he was laft turned out, were fcarcely visible, but upon examining them after he had been out about three months, they were found to have increafed furprisingly. Notwithstanding this, they were not firong enough to counteract the preffure of the quarters, and the foot itfelt appeared to be rather decreased, which is contrary to what is ufual, for after having been turned out for a certain time, they in general become larger. So particular a cafe led me to turn my mind to a particular a particular method of cure. This I should hardly have found out, if chance had not at that time put into my hands Lieutenant Moor's narrative of Captain Little's detachment. In page 93 of this book is the following paffage: "The bigotry with which all fects of Hindoos adhere to their own cuftoms, is well known: ftill, when these customs are frikingly injudicious, and totally abftracted from religious prejudices, perfeverance degenerates into obftinacy, and fimplieity into ignorance. So it is with the Mahrattas, in abiding by their prefent practice of cutting the hoof and fhoeing horfes, they cut away the hinder part of the hoof in fuch a manner, that the pastern almoft touches the ground, and the frog is fuffered to grow fo, that the hoof is nearly a circle, in which form the fhoes are made, the hinder parts almoft touching, and fo thin, that a perfon of ordinary ftrength can eafily twist them. Inftead of making the back part of the hoe the thickeft, they hammer it quite thin, making the fore part thickelt, and the fhoe, gradually becoming thinner, ends in an edge." "This mode of fhoeing, in a country where-from the nature of the climate the horfe's feet are probably very strong, did not ftrike me to be quite fo injudicious as the author above-mentioned represents it. I determined, therefore, to try on this particular horte a fhoe, in fome refpects fimilar to thofe above defcribed, that I might fee whether it would alter the fhape of his foot: fince it is faid to make " the frog grow fo, that the hoof is nearly a circle," which was the very effect that, in this cafe, I wished to produce. I therefore ordered my fmith to make a fhce at my own forge, in the form I generally ufe, (which will be hereafter defcribed) with the following exceptions: the web of it was almoft to cover the fole, room being given to admit a picker; and, as it proceeded to the heels, the web on each fide was to be continued as far as the cleft which feparates the bars from the frog. He was to make the "fore part the thicket, and to hammer it fo thin at the heels, as for it to end in an edge," by which “a perfon of ordinary ftrength could eafily twit it." P. 56. Mr. Freeman confequently tried the experiment, which he minutely relates, and found it anfwer to the utmost extent. The last part of the work confiders the best mode of shoeing, fo as to defend the foot, without interfering with the motions of its different parts, on which the fpring depends. The particular mode recommended is as follows: "A fhoe for a good footed horfe cannot be made too flat, it should be rather narrower at the heels than at the toe, and of fufficient fubftance, in proportion to its fize, to prevent the iron from bending. A fuller is perhaps of fervice to protect the heads of the nails, and fhould be made nearer or further off from the edges of the fhoe, in proportion to the thickness of the wall, but it has its difadvantages. For where the fuller muft be very near the edge, as in the cafe of a thinfooted horfe, it contributes to wear out the fhoe more rapidly at the toe. It may alfo, as the Earl of Pembroke obferves, " caufe a partial yielding." "When a groove is made round the edges of a fhoe, an even pur chafe of the wall must be taken throughout, whereas, in a bad foot, a greater greater hold might have been taken on fome parts of the wall to fave the others. "Smiths, in general, are apt not to put the fuiler coarse enough, in order, as they fay, to make their work look neater. The nearer the fuller is put to the edges of the fhoe, the higher the nails are obliged to be driven, to take their hold, and confequently the more liable they are to injure the foot. If the fuller be put more coarfely (that is, not to near the outward edges of the fhoe) the nails must be driven more flaming, and not fo high, they confequently take more hold of that part of the hoof where the cruft is the thickett, and are not fo liable to fall out. No nation, I believe, except the English, and thofe who imitate the Englifh, make a fuller to the fhoe: but inftead of making the holes upon an even line, they put them more or lefs on the outfide of the fhoc for a bad-footed horfe, in proportion to the hold they can venture to take. This they call percer gras, on percer maigre. Thefe holes thould be made at twice, firft by punching (or, as the fmiths term it, counter-fiaking) a large hole, not quite through, for the head of the nail to lodge in, and then by piercing a fmaller hole with a different inftrument, for the reit of the nail to go through. The heads of the nails will, by this method, be better protected, and kept in much stronger than when a fuller is made for them." P. go. The mode of fhoeing here recommended, is fuch as is fitted for horfes that carry light weights, and are not hard worked, which is the cafe with hunters, horfes kept in the riding-houfe, and those used for pleasure. The principle laid down is alfo to be kept in view, when fhoes are made for horses used in more fevere employments, but when applied to them, confiderable deviations will be neceffary for the defence of the hoof. We cannot allow ourfelves to go more at large into an article of this nature, judicious as we may think the execution of it; but recommend it to the perufal of thofe gentlemen who are defirous of gaining information, which to many perfons is important, refpecting the mechanifm and management of horfes feet. ART. III. A Differtation upon the Philofophy of Light, Heat, and Fire, in feven Parts. By James Hutton, M. D. and F. R. S. E. 8vo. 326 pp. 6s. Cadell and Davies. 1794. THE HE publication now before us forms a kind of fupplement to two great philofophical works by the fame author, the first of which was published in 1792, and entitled "Diletations on different Subjects of Natural Philofophy;" the other was noticed in the third and fourth numbers of our fixth vo lume, lume, and was called "an Investigation of the Principles of Knowledge," &c. in three volumes 4to. As the great extent of the latter work prevented us from following the author's fteps completely through it, we contented ourselves with fhowing, by fome examples, how ill-founded, and fometimes contrary to found logic, thofe pofitions were which he advanced ast principles; and, on the whole, concluded our account by warning our readers against the fophiftry of a theory, which promifed only to give them Deifm for their religion, and scepticifi for their philofophy." Severe as this opinion may appear, we have found no reason to relinquish it, and fhall take the occafion of the prefent work, fo intimately connected with the former, to explain more fully its foundations. One of the agents in the metaphyfico-phyfical machine into which Dr. Hutton would transform the univerfe, is the folar fubftance, or the matter of Light in general, to which he attributes abfolute levity, making it a principle opposed to gravity. For this purpose it is, that his two great works are filled with perpetual difcullions on the abstract ideas of extenfion, magnitude, form, motion, inertia, hardness, expansion, and the like; on which fubjects he attacks all received ideas, without fubftituting one on which the mind can reft. Thus it is that he leaves thofe readers in total fcepticism, whofe knowledge is but fuperficial, or who depend on him for information. It is on the phænomena of light, heat, and combuflion, that Dr. H. endeavours to found the whole fabric of his metaphyfics. On which fubje& we must here caution our readers, that it is only the latter of thefe which the Dr. calls fire: that is, what the philofophers, who retain the old name of fire to fignify the fluid which produces heat, expansion, &c. call by the name culinary fire, &c. in a word, combuftibles in a state of combustion. The difcuffions, generalizations, and deductions of Dr. Hutton on these three points, in his two great works, are fo long and diffufe, that we could not eafily purfue them without falling into the fame prolixity: it is therefore fortunate that, thinking he has found his fyftem confirmed by fome new facts, he has given us the opportunity of feeing him go over the 'whole within a narrow compafs. Some very interefting experiments of M. de Sauffure and M. Pictet, which he is defirous of applying to his theory, are the fubject of this recapitulation: in which we fhall find copious examples of the attention he gives to the important circumftances of phænomena, of the manner in which he reprefents the opinions he has occafion to attack, and of the courfe he takes to connect his Phyfics with his Metaphyfics. 3 The The first of the experiments in queftion, made by M. de Sauffure, (a naturalift, on whom Dr. H. beftows very just commendations) is defcribed in the fecond volume of that author's Voyages dans les Alpes, p. 353. It is this. It was already known, that if two metallic concave mirrors are placed oppofite to each other, at some distance, and in the focus of one of them be placed a burning coal, then any very combustible subftance, placed in the other focus, will take fire. On the general phænomenon, to which this fact belongs, M. Lambert had made various experiments, which led M. de Sauffure to fufpect that if, for the burning coal, there were fubftituted a body merely hotter than the general temperature of the place, it would raife a thermometer fituated in the other focus. For this new experiment he employed two mirrors of pewter, of a foot in diameter, and four inches and a half focus, which he placed at the diftance of twelve feet from each other. He put at one of the focuses a ball of iron, two inches in diameter, which, after having been red hot, had been kept in the dark, till it was no longer vifible. The confequence was, that it raised the thermometer, at the other focus, eighteen degrees of Fahrenheit's fcale. M. Pictet, to make it yet more certain that the heated body gave out no light, repeated the experiment, fubftituting, for the ball of heated iron, a fmall matrafs, into which he poured boiling water. In this inftance the thermometer rofe 3° Fahr. Before he defcribed thefe experiments, M. de Sauffure had fpoken of thofe of Lambert, who calls that heat luminous heat, which proceeds from the burning coals, and that obfcure heat, which is given out by bodies fimply hot. Thefe expreffions he employs only in thofe experiments; for in fpeaking of heat in general, he confiders it uniformly as the effect of a particular fluid, which he calls fire; and Dr. H. himfelf (p. 15) cites a paffage from this naturalift, where he precifely explains his meaning on this fubject. M. de Sauffure therefore, following for a moment the fame figurative expreffion, which Lambert had employed in the fame experiments, fays at first," that if it has the fuccefs which he expects, it will afford a proof that obfcure heat, as well as light, may be reflected, and condenfed in a focus." 46 This paffage is the fubject of perpetual cenfure to Dr. Hutton throughout his whole work. Heat," he fays, " as an external thing, is only a quality of bodies, it cannot therefore be the thing which is qualified; this would be lofing the diftinction of agent and patient, the thing heat as a caufe, and the confequence of that thing as an effect. The more then we fhould reafon upon fuch a mistaken principle, the more we fhould |