quick and amazing progrefs, by the affiftance of the fcience of nature. Without the knowledge of the true caufes and their connections, it is impoffible either to obviate or to remove all the obftacles arifing from chance or accidental circumstances. From what has been faid in a few words, it must evidently appear, that chemistry, in a peculiar maner, throws a great light on all mechanical trades, concerned with corporeal fubftances; how ever the property of the subject itself feems to prefcribe limits to this fcience. The quality of our fenfes, even when affifted and improved by art, will not let us penetrate father than to a certain point. The fubtlenefs of our inftruments is infufficient, and the best become at laft ufelefs. All thefe difficulties are ftill more increased, from the most fubtle particles which cannot well fall under the examination of our bare fenfes, having not only the greateft adhesion, and confequently exereifing the greateft refiftance to the attempts of dividing them, but alfo affording the most effectual and active means for this end. How imperfect therefore, must be our most perfect knowledge of the myfteries of nature? This is all perfectly right; and the pretenfion is fupremely filly, to be able at a future period to inveftigare the firft powers, which the Creator has eftablifhed at the creation and for the prefervation of the material world. Such a science is too abftrufe, and reaches beyond our attainment; it is referved for the power of the Creator, and not for that of a creature. But it by no means fol lows, that chemistry should not be able to difclofe to our eyes many a scene of wonders. Could we only discover with certainty, the elementary principles of bodies (principia proxima) together with their connections and pro. portions, chemistry would be able to do great things. From the most early periods, certain fubftances were thought to be fo fimple, that art gave up all hopes of analyfing them any further, and thefe were therefore confidered as the ftamina prima. Such are more especially the four Ariftotelic elements, earth, water, air, and fire: to difcover the compofition of which is the bufiness of higher and more refined chemistry. Let us therefore examine, whether all hopes are entirely loft of difcovering any thing here.Earth is the fixed principle, which remains after the fire has exerted its deftroying power against a body, and which is not foluble in water in the common way. This is the coarseft of all the four common elements, and makes but a fmall part of the bodies. Whatever analyfis has hitherto been able to establish with certainty, may be reduced to this; that earth (which after all proves to be of different fubftances) is by no means the fame matter, nor homogeneous, but a compound of feveral; and is found to be more or lefs of a faline nature, at least it is fo on the furface of our globe, in its moft pure ftate. There have been found fix different fpecies; having all quite different properties, and which hitherto have neither been decompounded into more fimple, nor been chang ed into another: viz. 1. The earth of of the ponderous Spar; 2. calca reous earth; 3. magn fia; 4. clay; 5. filiceous earth; and 6. earth of gems. I have in another place mentioned the characteristics of them. Whether thefe, which till a further investigation may be called primitive earths, are really different, or only varieties of the fame, I cannot tell; the laft opinion feems to be the moft fimple. I have however before obferved the dangerous error of limiting the order of nature to our confined ideas. The conclufion ought not to be formed before the premises are afcertained by experiments. Patience and affiduous application may perhaps in future times make difcoveries; fince we have at leaft fome confiderable number of notions about their properties, by which a great deal is already gained. But fince the acid of fluor and water, meeting one another in the form of vapours, coagulate into filiceous earth; and acid of arfenic with phlogifton coagulate into folid white arfenic; there is fome indication that ter. reous fubftances, as well as metallic calces, may be confidered in their firft principles as acids; which in the firft cafe are become fixed by water, and in the laft by phlogifton. Thus much at least is certain, that nature has indicated itself to be poffeffed of an abundance and variety of acids; and that it particularly employs them in its various operations. Water is ftill more fubtle, and with more difficulty decompounded. Upon more accurate examination we find, that the experiments according to which it was imagined, that water could be changed into earth, do by no means prove that which in the beginning had been fufpected of them. It is generally known, that heat caufes peculiar changes in water. The particles of water ftrongly attract the particles of heat; and after they have been charged with, or enveloped by a certain quantity of them, this compounded matter becomes fo eafily moveable, that its fu face endeavours conftantly to form a horizontal line; it has a great fimilarity with a fubtle earth melted by fire. If you diminish the heat, by which operation the furface of the particles either come in contact, and by their friction hinder this reciprocal motion, or the elafticity and power of repulfion is fufficiently diminished by the feparation of one of thefe elementary principles, then the mafs becomes indurated and ice is formed. It is not yet determin. ed, which of these causes is here prevalent. if ice is to be melted, a quantity of the employed heat is loft, amounting to very near 72° of our thermometers, and forms a kind of faturation; fo that its effect is concealed by its union with the ice, almost in the fame manner as if an acid were hindered from exercifing its characteristic properties by a faturation with alkalies. The fame takes place with quicklime it: contains heat, which is inactive till a ftronger elective attraction fets free and expels it. By the abforption of 72° of heat, ice, is made fluid; that which it receives beyond it is fuperfluous; which may be easily obferved, in the fame manner as in adding an acid to a neutral falt: the water expands, grows warmer, more fub G 3 tle, tle, more penetrating, moveable, and light. If the quantity of heat is accumulated till it becomes equal to 100°, it is diffolved into elaftic vapours; fome of which are already generated before the degree of heat is equal to 100; but fo much the lefs, the lefs the quantity of heat exceeds the abovementioned degree of faturation.In the very moment they are feparated from the mafs it cools; for all evaporation generates cold. Does this cold arife because the increased volume requires more to its faturation, and can in confequence of its effect, fix more heat than before? Or is the heat (which was united to the water and was increased to a certain degree) now enabled to confolidate itself clofer and in greater abundance, and to carry off in confequence that part of the water which is nearest at hand? -This is what experiments have taught us of the compofition of water; plainly demonftrating that it by no means ought to be confidered as a fimple fubftance. divide light (the infinitely fubtle light) into colours, has opened the way to many very curious myfteries of nature, though it was no more than a mechanical divifion. Mr Scheele difclofes a more fubtle, because a chemical analyfis; which inftructs us not only about light, but alfo about fire, whofe explication has hitherto been the crux philofophiæ. I have, with feveral alterations, repeated his principal experiments on which he grounds his doctrine on this fubject, and found them perfectly accurate. Though in fome less material circumstances a nearer confirmation might become neceffary; it does however no injury to the main fubject; which is grounded on feveral correfpond. ing experiments. Heat, fire, and light, are, in regard to the elementary principle, the fame with good air and phlogifton; but their proportion, and perhaps the manner of their compofition, caufe the great difference. Phlogifton seems to be a real elementary principle, which enters the chief part of fubftances, and adheres to them moft obftinately. There are feveral means to feparate it more or lefs perfectly: of those known fubftances, good air is most ac tive; for which reason, I put its fign at the very top of the column of phlogifton in my new table of attractions; what it cannot do fuddenly, is however done gra I have before mentioned fome thing about air, and proved, that the fubftance commonly called by that name, is by no means a finiple and homogeneous body. I need not likewife be prolix on this, and the thus called fourth element or fire; fince these two are the objects of the following performance; whofe author, Mr. Scheele, has great merit in che-dually by the intervention of famistry by feveral important dif- vourable circumftances. coveries; all his inquiries fhewing not only his reflection and reafoning, but also a peculiar fkill and perfeverance in inveftigating truth, both by analysis and by fynthefis. Newton's discovery to How interefting the more refined chemistry is, will not be ne ceffary to prove more circumftan tially on the prefent occafion. It requires a great deal of prejudice, or the greatest ignorance, to treat it with contempt under the fpecious pretence of unneceffary refinement and fubtleties. Earth, water, air, heat, light, and many more fuch fubtle fubftances are every where to be met with; and as long as their properties remain unknown, the effects both of nature and art, must remain involved in the most perfect ob fcurity. In chemistry, there are none of the veritates otiofe; the leaft phænomenon, when examined in all its caufes, is always connected with others of the greatest importance; in such a manner, that every thing is fhewn connected in the great economy of nature. G USEFUL USEFUL PROJECTS. Obfervations on the Dyfentery of the Weft Indies, by B. Mofeley, Surgeon at Kingston in Jamaica; with his new and fuccessful Manner of treating it. THE HE caufes of all difeafes, well understood and properly confidered, point to their -It is an obfervation of the great Sydenham, that "he never was at a lofs to prescribe for a difeafe, when he knew the cause of it," and that he always prefcribed with caution until he had found it. The diforder in question has been, I believe, more confidered from its effects, its remote, and concurrent caufes than from its immediate caufe: hence we may account for the inefficacy of the various attempts to cure it. The p-n of writers has done little more in the bloody flux, than record the times and places when and where it proved moft fatal; the appearance it put on; its tymptoms; its devaftation ; variety of modes of treatment that had no certain fuccefs: now and then a remarkable cafe, and the phenon.ena difcovered on diflecting the dead, The great author above men tioned, following nature as an unerring guide, never stopped at effects, but proceeded on to the caufes of difea es; and affifted the means employed by nature to remove them, or substitute a fafer and better me hod;-to which principle the world is indebted for that ineftimable work that can only perish with it; a work founded in nature, on a bafis applicable to all climes; that stands as the Palladium of phyfic against the fuperftitious errors of the middle ages, and the ingenious chimeras of later times ;-he difcovered the dyfentery to be, "a fever of the Jeafon, or of its own kind, turned inwards upon the inteftines ;" and yet his fucceffors have made but little father use of this excellent aphorifm, than quoting it, as their rules laid down for treating the disease fufficiently pove. In the courfe of twelve years experience in this island, and from every account i have been able to procure from all parts of the Weft Indies, I have invariably found the truth of Sydenham's opinion; and have remarked that as the flux diftinguishes, by the num ber |