We have been particular in our account of thefe memoirs; both as the experiments related in them feem decifively to determine this long agitated question, and as they prefent us with a fingular phenomenon ;-the folubility of glas in water, under particular circumftances. We fhall only further obferve that it is fomewhat surprising that M. Lavoifier does not on this occafion take notice of an observation of M. Cadet, a Brother Academician, which renders his folution of the prefent problem more plaufible than it may appear to be at first fight. In the Memoirs of this Academy for the year 1767, that gentleman mentions a procefs by which he declares that he has diffolved glafs in water, by means of each of the three mineral acids.A fhort account of this process has been given in our Appendix above referred to f.

MEMOIR III. On the Variation of the Magnetic Needle, at Paris. By M. Le Monnier.

In this Memoir M. Le Monnier has collected the observations that have been made of the magnetical variation at Paris; from which it appears, that from the year 1666, when the needle pointed precifely to the north, its annual variation to the weft has increased till a certain period; and that the velocity of this change was greatest about the year 1684;-that the needle afterwards moved more flowly to the weftward; and that there are reasons to conjecture that the time is not very distant when it will become stationary.

MEMOIRS IV. and V. On the Petroleum of Parma, and on the inflammable Vapours that arife from the Earth in fome Parts of Italy. By M. Fougeroux de Bondaroy.

The first of thefe Memoirs contains many particulars relating to the manner in which the light mineral oil, called Petroleum, is collected in wells dug for that purpose, at the distance of a few leagues from Parma. In the fecond, M F. describes the phenomena attending a vapour which rifes from the furface of the earth in fome parts of Italy, and which catches fire on applying a lighted candle to it. The flame however is fo weak that, though it will speedily confume pieces of paper, or other light inflammable fubftances thrown into it, it will not kindle them. From many circumstances, and particularly from the fmell of the earth from which this vapour proceeds, the Author attributes the phenomenon to the Petroleum with which he suppoles it to be impregnated.. He confirms this folution by an experiment made with fome of the earth taken out of one of the PetroAcum wells near Parma, which exhibited the fame phenomena in miniature.

+ See Appendix, vol. 45, page 522.

MEMOIR VI. On the Metallic Rods defigned to preferve Building's from the Effects of Lightning; and on the Method of conflrulling them, &c. By M. Le Roi.

Not a fingle Conductor, as we learn from this Memoir, has yet been erected in France. This difinclination in our neighbours to adopt a beneficial improvement, may, we apprehend, in a great measure be attributed to the late Abbé Nollet; who ftrenuously and repeatedly reafoned and declaimed against the practical application of Dr. Franklin's discovery to the securing édifices from the dangers of lightning. In this Memoir M. Le Roi firft takes pains to clear up the doubts which, it feems, fome of his countrymen even yet entertain, of the identity of lightning and artificial electricity, and confequently of the identity of their effects. He then defcribes the most proper method of conftructing Conductors; and terminates the Memoir by anfwering two objections which may and have been made to the adoption of them. Some have objected that they are useless or inefficacious; and others, that they are dangerous. The first of thefe objections does not deserve an answer. And further, the fixing of a metallic Conductor to a house is a matter attended with fo little difficulty, and with fo fmall an expence, when compared with the value of the building, that it is not an object of confideration. Viewing even the erection of a Conductor as a mere work of fupererogation, on account of the comparatively fmall number of houfes that are injured by lightning; the expence cannot be ill beftowed upon a building, if it even an fwered no other purpofe than that of quieting the apprehenfions of its inhabitants.

As to the danger to be apprehended from an apparatus of this kind, on a fuppofition that it may attract the lightning, M. Le Roi justly observes that if it does attract it, it is undoubtedly qualified to tranfmit it to the carth, if the Conductor be of a fufficient thickness; and if it does not attract it, it can at least do no harm.-But it is needless to dwell any longer on this subject, in this country, where the utility and fafety of metallic Conductors, and the beft method of conftructing thefe preler vatives are fo well understood.

MEMOIR VII. Reflections on Hydrometers. By M. Le Roi. Without repeating what we have formerly faid on this fubject, in our account of M. de Montigny's Memoir on the Hydrometer (in the Appendix to our 46th volume, page 687) we fhall only observe that M. Le Roi's principal object in this Memoir is to propofe fuch a conftruction of thefe inftruments, as may give them the advantage of being comparable with each other; fo that a workman, after having conftructed one after his principles, may make others all fimilar to each other, and

which fhall indicate the fame degree on the fcale, on being immerfed in the fame liquor, fuppofing its temperature to remain the fame.

Of the three remaining Memoirs of this clafs, one contains fome miscellaneous obfervations on the fulphureous waters in fome parts of Italy, by M. Fougeroux. In the next, the true nature of jet feems to be afcertained, by the difcovery of a piece of foffil wood that was found at a confiderable depth in the body of a mountain near St. Germain en Laye, and which in all its fenfible qualities appeared to resemble that substance. The last contains the ufual botanical and meteorological obfervations annually prefented to the Academy by M. Du Hamel.

ANATOM Y.

The first paper in this class contains fome obfervations on the female organs of generation, by M. Portal: In the fecond, the fame gentleman prefents the Academy with fome remarks on the ftru&ure of the thoracic duct, and receptaculum chyli: and in a third Memoir he communicates fome miscellaneous obfervations on various points of anatomy.

The fourth and laft article of this clafs contains fome obfervations collected by M. Morand, on that particular fpecies of monitrous conformation, to which M. Maupertuis, we believe, first gave the name of Sexdigitifm; the firft inftance of which on record occurs in facred writ, where [2 Samuel, chap. xxi. v. 20.] we read And there was yet a battle in Gath, where was a man of great flature, that had on every hand fix fingers, and on every foot fix toes, four-and-twenty in number.'

At the reading of this Memoir, M. Morand fhewed the Academy the foot of a perfon which had eight toes: but the mott remarkable of the family of the Polydaclili was a man, a drawing of whofe skeleton is given in Kerkringius's Spicilegium, who had feven fingers to each hand, eight toes on the right foot, and nine on the left. These fupernumerary toes and fingers however coft their unfortunate proprietor his life; for he was drowned in the river Ya, near Amfterdam, in conformity to an ancient law againft monsters.

From the inftances collected by the Author it appears that Polydactilifm is frequently, though not conftantly, tranfmitted, both by the father and mother, to their immediate as well as more diftant pofterity. It appears like wife that this peculiarity of conformation has not fhewn itself in some of the children of a Sexdigitif, yet has re-appeared in the next generation. The moft whimsical of the freaks of Dame Nature, in the myfterious process of generation, fuppofing the mother to have been honeft, is that of a young girl lately hewn to the Academy, who had

fix fingers on her right hand, and foven on her left, while to ber after Nature had, penuriously, on one of her hands, bestowed only a thumb, without any fingers.

The fifth and laft Memoir contains only a few obfervations on the structure of fome parts of the fea-calf, by M. Portal. CHEMISTRY.

3.11

In the firft Memoir that occurs in this clafs, M. Jars gives the refult of his inquiries and large experience in the Metallurgic Art; and particularly defcribes a new and advantageous method of feparating filver from an, admixture of copper and litharge. On expofing thefe matters, mixed with powdered charcoal, to a moderate fire, the litharge is revived into lead, and as that metal flows with a heat much inferior to that requifite to melt. the copper, it runs into a bafon and carries with it the filver which it has feparated from the copper. The filver thus united only with the lead is cafily feparated from it by the ufual practice of cupellation. The copper however fill contains fome filver, though in a fmall quantity; but this may easily be feparated from it, on adding more lead, and repeating the preceding process; or ftill better, by adding a mixture of lead and martial pyrites. By this ingenious combination, which has been likewife practifed by the celebrated M. Cramer at the works at Blakenbourg, and which is founded on a scientific application of the doctrine of the chemical affinities of the fubjects employed, the product is increased, and the operation is greatly facilitated and rendered lefs expenfive.-But for the philofophical theory of this and other improvements in the docimaftic art, contained in this Memoir, we must neceffarily refer those who are interested in this branch of knowledge, to the article itself.

In a fecond Memoir, the fame ingenious Metallurgift, who feems to have vifited nearly all the mines in Europe, and who intended to have given a defcription of them, accompanied with remarks on the methods of working them, defcribes the Tin Mines in Cornwal: and in a third, he gives an account of the method ufed in the two great works in Derbyshire, of converting lead into minium. By the death of this active and zealous Academician the Public are deprived of a great number of valuable materials relating to Metallurgy, which he had collected in the courfe of his travels..

The laft Memoir of this Clafs contains fome obfervations made by M. Le Sage, on the hiftory and chemical analysis of the Lapis Calaminaris, found in the County of Somerset, and in Nottinghamshire.

GEOMETRY,

This Clafs contains only three Memoirs, on differential equations, by the Marquis de Condoreet.

ASTRONOMY.

ASTRONOMY.

MEMOIR I. On the true Diameter of the Sun. By M. De la Lande.

MEMOIR II. On the dark Protuberance obferved on the Disk of the Sun, during the Tranfits of Venus. By the fame.

Aftronomers have fufpected for fome time paft that the fun's diameter appears to be relatively diminished, in proportion as it is viewed through telescopes of a greater magnifying power. This appearance, it is fuppofed, proceeds from an augmentation of the apparent diameter of the fun, produced by a luminous circle or crown furrounding his real difk, and depending on the aberration of the folar rays; the effect of which aberration is neceflarily diminished in long telescopes, because in them the convexity of the object glass is lefs, and because the image is larger.

After an examination of the different obfervations of the late Tranfits of Venus, particularly of the internal contacts at the ingrefs and egrefs, M. de la Lande has been confirmed in the dea which he had entertained concerning the cause of this optical augmentation of the fun's difk; and upon the whole he concludes that the diameter of the fun, which he had determined, in his aftronomical tables, to be 31' 31" in the apogee, ought to be diminished about 6 feconds and; by which quantity therefore the duration of the Tranfits of Mercury and Venus over his furface ought to be diminished.

In the fecond Memoir M. de la Lande attempts to account, by means of this crown of aberration, for the appearance of the protuberance, or dark ligament, as it has been called, that was obferved about the times of the internal contacts, in the two late Tranfits of Venus in 1761 and 1769. It is difficult to give his explanation of this phenomenon, without the figure accompanying it. Perhaps however the following account of it may afford the Reader fome idea of his folution.

The crown or circle of aberration abovementioned is only an apparent extenfion of the real circumference of the folar difk; or, is only a luminous but unfubftantial ring, formed by rays fcattered on all fides from the real limb. When Venus actually touches the true limb of the fun, fhe intercepts from our eyes the rays which come from this border; as they are emanations proceeding from a part of the difk which is intercepted from our view. Thus the whole of this part of the luminous crown ought to appear dark, like the body of Venus; and this ligament or black protuberance ought to extend as far as the circumference of the adventitious luminous border. It ought to become smaller in proportion as the fegment of the fun's disk, concealed by the body of Venus, becomes lefs: and as foon as a fingle point of the fun's real circumference becomes vifible,

the