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The explication which this ingenious Academician gives of the effects of this celebrated inftrument, is recommendable for its fimplicity; his defcription of fome new dropburi, conftructed upon the principles which have been here ascertained by the most accurate experiments, is very curious, though fuccinct; but it would be difficult to render it perfpicuous to the Reader without the affiftance of the plates.
Concerning the Nature of the Earth, which is the Bats of the vegetable and animal Creation. By M. ACHARD. When any portion of animal or vegetable matter is fubjected to the combined action of air and fire, there remains, after the intire difperfion and evaporation of the volatile parts, a fixed rendue of a grey colour, which, by a calcination, continued for fome time longer, becomes intirely white. This refidue is a mixture of fixed alkali (united fometimes with other falts), and of the earth, from which the part of the vegetable or animal, that was burned, derived its folidity. In order to obtain this earth alone and feparated from all other matter, nothing more is necefiary than to Îixiviate the refidue with diftilled water. By this process all the faline particles are removed, and the earth, that formed the bafis of the calcined vegetable or animal matter, remains alone in its moft perfect ftate of purity. This is the method that has been followed by our ingenious Academician. He gives us accordingly a circumftantial account of thirteen experiments, which be made in order to discover the earth that conftitutes the bafis of vegetables—but of there we can only specify the refults. Ift, the earth, already mentioned, diffolves, with effervefcence, in all acids:―adly, it forms, with the marine and nitrous acids, falts per deliquium, that are not fufceptible of cryftallization:3dly, the marine acid adheres to closely to the earth of vegetables, that the action of fire, alone, is not fufcient to feparate them: -4thly, the marine falt, of which this earth is the bafis, is fufceptible of decompofition by the vitriolic acid, and all the faline alkalis, except the cauftic volatile alkali ;-the cafe is the fame with the nitrous falt which has vegetable earth for its bafis:— 5thly, heat alone is fufficient to carry off the nitrous acid that is united to the earth of vegetables:-6thly, this earth, faturated with the nitrous acid, acquires, by calcination, the property of fining in the dark, provided it be previously exposed to the light 7thly, the vitriolic acid, in conjunction with this vegetable earth, forms a falt, which fhoots into fmall cryftals, and requires a large quantity of water to diffolve it:-8thly, the action of fire alone is not fufficient to separate from the vitriolic falt (whole bafis is vegetable earth) the acid, that is neceffary to the prefervation of its faline properties:-9thly, the vegetable carto decompounds cinnabar, by uniting itself with its fulphur, and difengaging the mercury, with which it was mineralized :—
11thly, the fame earth decompounds fal ammoniac, and difengages from it the volatile alkali:-12thly, it alfo becomes at leaft, in part, by the means of calcination, diffolvable in water:-13thly, fixed air, if it be joined with calcined vegetable earth diffolved in water, will immediately occafion its precipitation. Now as all the properties of the vegetable earth, that we have here enumerated, are precisely the fame with those which characterise calcareous earth, and distinguish it from all other earths yet known, it is not without reafon that M. ACHARD confiders the vegetable and calcareous as one and the fame earth.
From this our Academician proceeds to an account of seventeen experiments, which he made on animal earths; we fay earths, for it appears from thefe experiments that there are two kinds of animal earth, one which has all the properties of calcareous earth, another an alkaline earth, different from all those hitherto known. He examines the opinions of Meffrs. Buffon, Baumé, and Poerner, relative to animal and vegetable earths, refutes them with modefty and evidence, and concludes this memoir by the relation of an interesting experiment, that renders his refutation victorious and unanfwerable.
A Memoir concerning the Force with which folid Bodies adhere to Fluids, determining the Laws, by which that Force is directed, conformably both to the Nature of the Fluid and the Solid. By M. ACHARD. This piece is not fufceptible of any abridgment that would be intelligible without the twelve tables in which the ingenious Academician has placed, in order, the refult of his experiments.
A Supplement to the Memoir concerning the Topaz of Saxony. By M. MARGRAFF. This Academician had promised to give a fuller account of the gelatinous matter, which he found in his operations on the Topaz of Saxony by the means either of falt of tartar or spirit of vitriol, and he relates here the different experiments he had made with this view. From these experiments it appears, that the gelatinous matter derives its origin from falt of tartar calcined, digefted with the vitriolic acid, and that it perhaps is united with a part of the calcined Topaz.
Concerning the Changeable Stone (otherwife called the Oculus Mundi). By M. GERHARD. The firft naturalift, who spoke with precision of this fingular stone, and pointed out its diftinctive property of opacity in the air and transparence in water, was the celebrated Boyle. The greateft part of the German writers on Natural History have done little more than copy him; and one of them (Ihie) has given to this ftone the name of Hydrophanus, from the property already mentioned. These authors had only feen detached fragments of the stone in queftion, without knowing any thing of its natal bed; and this circumftance
_circumstance rendered it so rare, that one, about the fize of a pea, was fold in London for two hundred pounds. It is now known, that the caulus mundi is to be found in the mines of Hartz, and (as our Academician obferves) in fome places in Silefia. Baron Veltheim vice-captain, of the mines of Hartz, fent a fragment of it to M. Gerhard, which occafioned the experiments mentioned in this memoir, of which is will not be amifs to prefent to the lovers of Natural Hiltory the following fummary:
The cuius mundi is folid and compact, and yet there are neither filaments, grains, nor any fort of foliation difcernible in it: When broken it refembles potter's earth, trong y baked, or fine China ware; when ftrack against steel, it does not give fire, fo that it is inferior in hardnefs to quartz, flat, and jafper; it rather approaches in its qualities to the ophie and the jade and its parts may be feparated with the knife. Though foft, it is fufceptible of a fine polish; thofe are so more especially whofe colour refembles ivory, and which are diftinguithed by fpots of a milky white: feveral of thefe ftones are of a greenish hue, variegated with white ftreaks, others between green and yellow, with ftraw-coloured fpots, others, again, brown; it is not yet known, with certainty, whether thefe colours are the effect of a metallic principle; our Author thinks it probable, from his having difcovered ferrugineous particles in the brownish Silefian Oculus Mundi. Its specific gravity is to that of water as two to one, or thereabouts, and it does not, when rubbed, become electric; nay, it acquires but a small degree of electricity, even by communication.
As to the natal bed and the manner of finding this ftone, Baron de Veltheim obferved to our Author, that it envelopes, in an opaque covering, the opal and the calcedonius of Iceland and the Ifles of Ferroe, and alfo the opals of Bavaria and Saxony, especially that kind which is diftinguished by the denomination of lapis piceus. In this form, its external afpect is grofs and porous, but its inner parts, which are contiguous to the opal or calcedonius which it covers, are more compact and of a finer grain. Sometimes alfo it is found in beds, among beds of the calcedonius, so that the former appear milkwhite, and the latter greenifh or black. Besides the places already mentioned, the oculus mundi is found at Kosemutz, in the duchy of Nimpfch, and, in a still greater abundance,, at Grache in the duchy of Munsterburg; it is in this latter diftrict
Our Academician, we apprehend, is mistaken, when he fuppofes a refemblance between this ftone and the jade, for the jade is much harder than the jasper.
that it appears in the form of an envelope to the green, yellow, and white chryfophrafus.
M. GERHARD, made fixteen physical experiments on this fingular ftone, and fome chymical ones. The refults of the former are as follows: 1. The oculus mundi or hydrophanus imbibes fluids like a fpunge, as appears from the increase of its weight, when it has been fometime, in water, and other experiments.2. The fluids that diffolve fat or unctuous fubftances accelerate the transparence of this ftone; which fhews that it contains particles of this kind.-3. The inconfiderable fpecific gravity of the oculus mundi fhews that it is very fpungy and porous.-4. The pores, however, of this ftone must be very fmall, fince they admit no particle of the folid substances that have been diffolved in fluids.-5. The oculus mundi becomes tranfparent by the affiftance of fluids, exactly as paper and other fimilar bodies, when they have abforbed a fluid. The rays of light are attracted by the fluid, which has entered in a large quantity; and the pores of the ftone, being thus widened, give the rays a paffage in right lines, and thus produce transparence.
The chymical experiments made on this ftone by M. GERHARD fhew, that it is compofed of earth of alum, of vitrificable earth and an unctuous matter, in fuch proportions, that the first of thefe, conftituent parts makes two-thirds of the whole-from hence it appears, that the oculus mundi cannot belong either to the genus of quartz, or to thofe of flint, agate, onyx, jafper, or any other vitrificable ftone, but that it muft be placed in the claís of unctuous, aluminous ftones, formerly called argillaceous and apyri. Thefe confiderations have led our Academician to confider the oculus mundi as a kind of fmectite, in which cafe its defcription would be smettis porofus, in aere opacus, in aqua pellucidus. There are many acute obfervations in this piece, which we muft pafs over in filence, but which render it peculiarly worthy of the attention of Naturalifts.
An Extract of the Meteorological Obfervations made at Berlin in 1776. By M. BEGUELIN.
Concerning the Alteration of the mean Motions of the Planets. By M. de la GRANGE.
Solutions of fome Problems in Spherical Aftronomy, by the Means of Seriefes. By the fame.
Concerning the Ufe of continued Fractions in the integral Calculus. By the fame.
Concerning a Problem in plane Geometry, which is looked upon as difficult. By M. de CASTILLON. Nine plates, with figures, are given to illuftrate the folution of this problem.
Concerning a new Property of Conic Sections. By the fame. A Memoir, containing, 1. Obfervations of the Occultations and Re-appearances of the Anfa of Saturn's Ring, in the Years 1773 and 1774.-2. Obfervations of feveral luminous Points frequently feen on the Anfe of the Ring, which justify a Conjecture that the Ring is an Earth, which has Inequalities.-3. Obfervations of the three Oppofitions of Saturn in 1773, 1774, and 1775, in order to afcertain the Place of that Planet.-4. A Chart of the apparent Courfe of Saturn, which represents the four Obfervations of the Occultations and Apparitions of the Anfæ. By M. MESSIER. Extract of a Letter from M. Euler to M. Beguelin, dated in May 1778. This letter relates to firft numbers.
Extract of a Letter, written from Petersburg, by M. Fufs to M. Beguelin. June 1778. Relates to M. Euler's method of examining great numbers, in order to find whether or not they are firft numbers.
Concerning the Immortality of the Soul, on the Principles of Natural Philofophy. By M. SULZER. Memoir III. Peace to the foul, and veneration to the memory of this excellent Philofopher, who being now got out of the region of doubt and conjecture, is gone to verify his fpeculations on immortality, and -videt quanta fub nocte jaceret noftra dies.-As for us, who regret his removal, and are yet to remain fome moments behind him, let us attend to the views that opened upon him, while he was paffing through this twilight of humanity. We gave an account * of his two former memoirs on this momentous subject: this third memoir, is indeed, a production that comes from the dusky region of conjectures. In the two former, the Author produced inconteftible facts to prove that the foul is a substance, different from the animal body, and that it continues to exist entire, after the deftruction of the body to which it had been united for fome time; but when he pushes his inquiries farther, he finds himself in the clouds. I am obliged, says he, to defcend into the night of the tomb, and to grope in the darkness. To comfort, however, both himself and his Readers, he defcants for a while on the innocence, pleasure, and utility of conjectures, and fhews, that the true philofopher ought not to reject these flender tapers in the unknown regions of truth, provided, in his dubious walk, he follows a route in which he cannot go totally aftray. I commend, fays he, the fage and modeft timidity of Locke, who never ventured to quit the thread of experience, to afcertain the folidity of the first principles of human knowledge: but I do not, on the other hand, blame the bolder fpirit of Leibnitz, who dared to foar higher. The
See Vol. Iviii. of the Monthly Review, p. 521.