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however, in a great measure prevented, by combining acids with the oxyds; because, in this case, there is a change effected in the elective attractions: the influence of this alteration will be evident to those who try the experiment with the different oxyds of mercury.

The reciprocal decomposition of metallic oxyds and ammoniac is so greatly accelerated by heat, that in some cases it takes place instantaneously with a violent detonation; as in the fulmination of the ammoniacal oxyds of gold and silver, either by fire, or by a flight degree of friction.

All these various phenomena depend on the attraction of the principles of the oxyds by those of ammoniac, and on that of acids by both these compounds. It is M. FOURCROY's intention more particularly to investigate these attractions with respect to each metallic oxyd; and, for this purpose, he has already performed a number of experiments on the decomposition of mercurial falts, which will be the subject of a future - memoir.

· Memoir on the Detonation of Salt of Glass, when thrown into Water while in fasion. By M. FOUGEROUX DE BONDAROY, .

* This substance is known among our workmen by the name of glass gall: if any of it happen to adhere to the ladle, when dipped in water, it will explode with great violence; and dreadsul accidents have sometimes resulted from not taking care to dry the ladle before it touches the metal. Tbe present academician observes, that this detonation never takes place, except when the flux has been prepared from such plants as contain fea-falt; of this kind is the Fucus maritimus vefic. hab. of Tournefort, which is much used for this purpose in the glasshoutes of Normandy and Bretagne. The salt of glass, made with soda of Alicant, contains only vitriolated tartar and magnefia, and never explodes.

Memoir on the Art of Eliquation, or feparating Silver from Copper by Means of Lead. By M. Duhamel,

We have here a very minute account of every part of this process, with a description of a new furnace invented by the author of the memoir. As it cannot easily be abridged, without tranfgrefling the limits to which we are confined, we must refer those who wish for information on this subject to the work itself.

Observations on the Process of making Alum by an immediate Combination of its confiituent Principles. By M. CHAPTAL.

This memoir is the ufual annual contribution of the Royal Academy of Sciences of Montpellier, and contains some useful bints. It is well known that the process in question consists in exposing the alumine to the action of the sulphuric acid: but as this acid is only a combination of water with the vapour arising from the combustion of sulphur, and is much more active in its elastic, than in its condenred state, M. CHAPTAL has found that much expence may be saved by exposing the calcined alumine to this vapour, instead of the concentrated acid. The lead, with which the apartment, or, as the workmen call it, the house, is lined, in which the process is carried on, is another expensive article, and this ingenious academician, after many trials, discovered a varnish which answers the purpose equally well: it is made of equal parts of piich, turpentine, and wax, melted together, and must be applied boiling bot. He describes the house, in his alum works, as 48 feet long, 44 feet broad, and 27 feet high ; to line this with lead would not cost less than 800,000 livres; whereas, by using the varnih, which has now stood above two years, the expence was not seven thousand. This varnish is impenetrable by water, and is not liable to crack; it is less viscous than tar, makes a smoother surface, and may be thickened, when necessary, by the addition of brick duft.

Memoir on the Combination of Metallic Oxyds with Alcalies and Lime. By M. BERTHOLLET.

It was formerly supposed that all those bodies which, by combining with acids, form a new substance, were of an alcaline nature : but M. BERTHOLLET has here Thewn, by a variety of experiments, that metals, combined with oxygen, form compounds which will easily unite with alcaline subé stances, and, with these, constitute falts; so that those metals, which are soluble in acids, and, in this combination, have acquired in some measure the nature and action of alcalies, become, when oxygenated, a species of acids, and, as such, contribute to the formation of saline substances.

NATURAL HISTORY.
Memoir concerning the Nutmeg Tree, or Myristica.

By M. De La MARCK.

We have already given an account of some microscopical observations on the flowers of the nutmeg, by which they were found to be hermaphrodites *: but M. DE LA MARCK, on the authority of M. Céré, director of the King's gardens in the Isle of France, describes thein as belonging to the class of disecia, and has given separate plates of the male and female flowers; which have a monopetalous trifid calix, without any * See vol, iii. of the New Series of the Monthly Review, p. 502.

corolla,

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corolla. No less than eight species are here described ; and we are informed that the myristica aromatica is cultivated with great fuccess in the Inands of France and Bourbon, and produces fruit not inferior to the nutmegs of the Moluccas.

Observations on the Species of Fucus that grows on the coast of Normandy. By M. Le Gentil.

This gentleman found that the stem of the Fucus Palmatus has generally an elliptic cavity, about five or fix lines deep, near the root, which is the abode of a kind of petella of an olive colour, like that of the plant.

Inquiry concerning the Shrub known among the Ancients by the Name of the Lotos of Lybia. By M. DesFONTAINES.

It is here maintained that this vegetable, which is very different from the lotos of Egypt, is that species of jujube which Linné calls the ramnus lotus: its fruit resembles that of the common jujube, but is larger, and of a more agreeable Alavour.

ASTRONOMY AND GEOGRAPHY. Concerning the Solar Eclipse, June 15th, 1787. By M. MonNIER.

From his observation of this eclipse, which, in Paris, commenced at 4" 27" 25" true time, on the western limb of the fun's disk, about five degrees below its horizontal diameter, M. MONNIER infers that, in the lunar tables used by the Board of Longitude in London, the moon's place is stated as too forward by 42".

Comparative Observations of the Solftitial Altitudes of the Sun. By the fame.

In the year 1738, M. Monnier observed, by means of a gnomon which he had constructed in the church of St. Sulpice in Paris, the difference of the sun's altitudes in the summer and winter solstice: from similar observations made in 1788, he concludes that the obliquity of the ecliptic is now ten seconds less than it was half a century ago.

Extract from the Astronomical and Physical Observations, made at the Royal Observatory, during the Pear 1788. By Messrs. CASSINI, Nouet, DE VILLENEUve, and RUELLE.

This memoir consists of astronomical and meteorological tables, to which we must refer our astronomical readers.

On the Inferior Conjunction of Venus, August 7th, 1788. By M. DE LA LANDE.

From the observations made by the Duke of Marlborough, Dr. Hornsby, and Dr. Maskelyne, M. DE LA LANDE, who

was

was at that time in England, computes the place of the aphelion of Venus to be io signs 8° 261.

Fourth Memoir on the Parallax of the Moon. By M. DE LA LANDE.

On the apparent Diameter of the Moon. By the same.

The former memoirs on the moon's parallax were published in the transactions of the academy for the years 1752, 1753, and 1756. M. De La Lande had then adopted M. Bouguer's hypothesis relative to the figure of the earth, and hence calculated the constant parallax for Paris to be 57' 3": but being convinced, by a number of experiments and obfervations made since, that the spheroidism of the earth is not more than Footh, he computes the constant parallax to be 56' 58", 3 for the latitude of Paris; 57' 5" under the equator; 56' 53", 2 at the pole, and, taking the mean radius of the earth, he reckons it 57' 1". Hence the moon's diameter is 32' 47",3, when the parallax at Paris is 60'.

Concerning the Diameter and Light of the Fourth Satellite of Jupiter. By the fame.

As objects become imperceptible when their diameters are viewed under too small an angle, it is obvious that the apparent will be greater than the real duration of eclipses of Jupiter's satellites : this difference is variable, and depends on the distances of Jupiter from the sun and earth, on the brightness of the planet arifing not only from its aspect, but also from its elevation above the horizon, and on the aperture of the telescope through which it is viewed. M. De Fouchy propoled a very ingenious method of ascertaining this difference, by applying diaphragms to the telescopes. M. Bailly put this idea into practice with respect to the three first satellites, and pub. blished a memoir on the subject in the history of the academy for the year 1771. M. De La LANDE has here applied the same principles to the fourth satellite, and has given formula by which the instant of immersion, the diameter of the satellite, and the proportion of its invisible segment to the whole disk, may always be found. In the sixty-third volume of the Philo. sophical Íransactions, is a letter from M. Bailly to Dr. Markelyne, communicating the particulars of M. De Fouchy's invention *.

On the Satellites of Saturn. By the same.

This memoir contains the observations and elements from which its ingenious author calculated the new tables of these

* See Monthly Review, vol. 1. p. 353, and vol. lii. p. 628.

satellites,

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satellites, published in the Connoisance des Temps for the years 1791 and 1792. · Memoir on Solar Eclipses and Occultations of Stars observed in the Years 1787 and 1768. By M. DE LA LANDE.

Memoir on the Eclipse of the Sun, August 16th, 1765, obferved in Rome. By the same.

The design of these two memoirs is to ascertain the longitude of the several places where the observations were made. The following are the principal results: Paris and Verona,

34' 42"
Gotha,

33' 331
Bagdad,
Leuenthal,
Leyden,
Perinaldo,

21'
Warsaw,

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St. Peter's, Rome,
Gothaab, on the west coast of ?
Greenland, in 64° 10 N.L.)

36 36' 26" Memoir concerning the Variation of Light in the Star Algol. By the fame.

M. DE LA LANDE, in consequence of comparing his own observations of this phenomenon with those of M. Goodrick and of M. Wurms of Nurtingen, determines its period of variation to be 2d 201 49'2".

Theory of the Satellites of Yupiter. By M. De La Place.

This memoir contains a complete theory of the several perturbations of Jupiter's moons, with the analytical calculations necessary for correcting the tables of their motions.

Observations on several Monuments of ancient Gothic Architecture in Paris, on which are carved the Signs of the Zodiac, together with some Egyptian Hieroglyphics relative to the Worship of Isis. By M. LE GENTIL.

Description of the Signs of the Zodiac in the Benediktine Abbey at Saint Denys. By the same.

Observations on a Differtation written by M. De la Lande, inserted in the Journal des sçavans for July 1788. By the same.

M. LE GENTIL observes, that the ligns of the zodiac here described have a great resemblance to those which have been discovered in India: hence, and from the similarity between the ancient Gothic and the Indian style of architecture, he con

jectures

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