Thefe Dialogues were followed by the Mechanics of Galilei, in which the usefulness of that fcience, and the inftruments it employs is particularly confidered, and which is followed by a fragment on percuffion. In this work the eminent Author, by an happy application of the law of Equilibrium, reduces all the theory of machines to the following fundamental principle, that in them the force, properly speaking, does not increafe, but that its operation is determined for a long space of time. In another work (intitled, Mathematical Difcourfes and Demonftrations concerning two new fciences, that are relative to mechanics and local motions, with an appendix on the center of gravity of certain folds) he applies the laws of mechanics to the theory of the refiftance made by hard bodies, when an attempt is made to divide them; and from this theory he deduces feveral confequences, of a philofophical kind.

There is ftill exifting in the library of Milan a manufcript treatife of Galilei concerning military architecture, where he has given, in 23 chapters, an explication of all the rules, that Marchi propofed with fo much obfcurity for improving the me thod of fortifying places.

Among the other fciences which owed much of their im provement to the genius and labours of this eminent philofopher, we may reckon accuflicks or the doctrine and theory of founds, as he was the firft who determined, with any confiderable degree of accuracy, the proportion of the length, thickness, and tenfion of the ftrings or chords of a mufical inftrument with the flats and fharps, or with grave and acute founds. The whitish colour of the moon, and the force of percuffion were the laft objects of his philofophical researches.

The ardour and affiduity with which he carried on his aftronomical obfervations, the conftant ufe of the telescope, and the coldness and moiflure of the nocturnal air, weakened, by degrees, his fight, and ended in total blindness, accompanied with other bodily infirmities, which he bore with the patience and refignation of a chriftian philofopher. After he had loft his fight, he endeavoured to fupply that defect by conftant meditation; but he gradually declined, and at length died at Arcetri, near Florence, in 1642, and in the 78th year of his age; the fame year that gave birth to Sir Ifaac Newton, who took up from Galilei the thread of aftronomical fcience, and carried it from world to world, through regions as yet unexplored and

unknown.

The funeral of Galilei was as obfcure as his education. The Florentines defigued to bury him in the church of Santa Crofa, near the tomb of Michael Angelo Buonarota; but fenfible that more splendid marks of honour, than the times would admit of, were due to his memory, they left his corps in a private place,

unul

until they could inter it in a proper and fuitable manner; but that time is not yet arrived, and this circumftance reflects little honour on the city of Florence.

There are many amiable features in the character of Galilei, fuch as fimplicity, cheerfulness, affability, opennefs, and mildnefs; and all these were agreeably feafoned with a propensity to mirth and pleafantry. Precifion and perfpicuity diftinguished him as a writer. Many of his works were unfortunately loft by the fuperftitious devotion of his wife, who facrificed them to the bigotry of her Confeffor.

AR T. VII.

Hiftoire de l'Academie Royale, &c.-The Hiftory and Memoirs of the Royal Academy of Sciences at Paris, for the Year 1772. Part 1.

4to. 1775

ΤΗ

HE great number and bulk of the papers read before the Royal Academy, during the courfe of the year 1772, have obliged the Society to divide the volume for that year into two

parts.

GENERAL PHYSICS. MEMOIR I. On the Flux and Reflux of the Sea; and particularly on the Equinoctial Tides. By M. de la Lande.

It is now agreed on all hands that the tides are one of the many effects produced by the univerfal gravitation of matter; and that the immenfe body of water with which a great part of the earth is covered, affumes the figure of an oval, or an elliptic fpheroid, the greater axis of which is pointed toward the moon, in confequence of the attractive power of that planet upon it. The action, however, of this general cause is variously modified by different circumftances; and the abfolute height of the tides in particular, M. de la Lande obferves, depends principally on the fituation of the coafts. In the middle of the Pacific Ocean it does not exceed a foot, according to the obfervations communicated to the Author by Mr. Banks and Dr. Solander. It rifes to three feet in the middle of the North and Indian feas, according to M. Gentil; and to five feet at the Ifle Rodrigues: whereas the tide rifes 46 feet at St. Malo's; which is the greatest height that it has been obferved to reach in any part of the earth.

The principal intention of the Author, in this Memoir, is to thew that the common obfervation refpecting the greater height of the tides at the equinoxes-an obfervation which appears not to be conformable to the theory of attraction-does not nevertheless furnish any reasonable objections to the truth of that theory for the phenomenon, he obferves, is very far from being conftant; and the winds, and the direction of the coafts,

003

are fufficient to furnish us with an explanation of it. At Peterfburgh, where there are no tides, the fea is raifed no lefs than five feet by a weft or fouth-west wind. On the whole, M. de la Lande concludes that the high weft winds which blow on the coafts in April and October, or at the equinox, increase the height of the tides at these times; that these high tides are not the effects of the increased attraction of the fun and moon at these seafons; and that they do not contradict the general theory, or, in other words, are by no means contrary to the fyftem of gravitation.

MEMOIR II. Obfervations on the Management of Sheep, &c. By M. Daubenton.

In this Memoir M. Daubenton relates the refults of the experiments which he has made, in oppofition to the common practice, in France of houfing sheep during the winter; and endeavours to fhew the advantages derived from the keeping them abroad during the whole year, according to the practice fol lowed in our own country and in Spain. MEMOIR III. On an Electrical Machine of a new Kind. By M. Le Roi.

This machine is no other than that which confifts of a flat circular plate of glass, invented, we believe, by Mr. Ramsden; but which M. le Roi has improved by infulating the cushions. By this means it is made capable of producing either positive or negative electricity, at the will of the operator.

This Article is followed by fome Inquiries into the horizontal Variation of the Needle, by M. le Monnier; and by the usual Botanicometeorological Obfervations, annually prefented by M. Du Hamel, Among the fhorter phyfical obfervations annexed to this clafs, we shall only notice the following:

Some artificial magnets have been fhewn to the Academy, made by the Abbé Le Noble, which greatly exceed in power any magnetical bars that have hitherto been prepared. One of thefe weighing less than two pounds, lifted a weight of 40 pounds. Another weighing only nine pounds two ounces fupported, in the prefence of the Academy, a weight of 105 pounds; and a third, made in the form of a horse-fhoe, which weighed about two ounces, lifted a weight of four pounds fix ounces. The great power of thefe magnets does not appear to be owing to any particular novelty in the process; but to the attention which the Abbé has given to the quality and tem pering of the fteel, and to the conftruction of the armature; which is found to be a very effential article, and which had not yet been reduced to any precife rules,

CHEMISTRY

CHEMISTRY.

MEMOIR I. On Zine; or, the Analogy between Zinc and Phofphorus eftablished and developed by a Series of Experiments. By M. de la Laffone. Firft Memoir.

Zinc was a favourite subject with Van Helmont and the alchemists; and its various and fingular properties have been pretty largely difcuffed by the modern chemifts; particularly by Geoffroy, Hellot, Pott, Malouin, and Margraaf. In the prefent Memoir M. de la Laffone prefents this femi-metal under a new and curious point of view; and endeavours to establish a striking resemblance between it and the phosphorus of urine; two fubftances apparently very diffimilar.

He commences the parallel by taking notice of the extraor dinary light afforded by zinc, on expofing it, without addition, to a confiderable degree of heat. This light is of fuch a dazzling brightness that the eye can scarce fupport the splendor of it. Zinc likewife, during this deflagration, exhales an odour resembling that of garlic: phosphorus exhales the fame alliaceous vapour. This fulguration of zinc does not take place, nor will it continue, unless there be a free access of air: which is likewise true of phosphorus.-When the Author exposed zinc to a violent fire, in veffels clofely luted, the whole of it was volatilised the greatest part escaping through the luting, and deflagrating among the coals; while the remainder was found adhering to the infide of the cover of the crucible, in a metallic ftate, or under the form of innumerable particles refembling mercurial globules.

The Author next proceeds to fhew the great refemblance between the phenomena produced by the mere action of the air on these two fubftances, in altering or rather decompounding them. In phosphorus, the phosphoric acid, greatly concentrated, and united with phlogifton, greedily attracts the aqueous vapours floating in the atmosphere, with which it unites ; producing an inteftine motion, or effervefcence, vifible through a magnifier. A proportional quantity of the phlogiston is left difengaged; so that nothing is wanting to produce a deflagration, but an increase of this inteftine motion, either by means of warmth immediately communicated to the mass, or by fric tion:

In a fimilar manner zinc is acted upon by the air, or rather the aqueous vapours in the atmosphere; which, according to the Author, effect a real decompofition, though in a flower, more difficult, and lefs complete manner, on account of its metallic nature and other circumftances. The furface expofed to it is tarnished, lofes its phlogifton, and is covered with a true çalx. This calx, however, or earthy substance, says M. de la Laffone, appears to contain the phosphoric acid; fince, on 004 restoring

reftoring phlogifton to it, it is rendered capable of producing a deflagration perfectly fimilar to that of phofphorus. He fuppofes that every fubftance fufceptible of fuch a deflagration, contains the phofphoric acid combined with phlogifton; at the fame time very properly acknowledging that this new theory, with refpect to the existence of the phofphoric acid in zine, confidered as one of its conftituent principles-though founded on numerous facts contained in the prefent Memoir, as well as on others which will be related in a fubfequent paper-is only offered by him as an hypothefis, or a probable conjecture.

The Author confirms the refemblance between the two fubftances by various other obfervations. He mentions the very fingular corrofion of an iron spoon, on ftirring zinc in fufion with it; and its corroding and spoiling files ufed in rasping it. Thefe effects he afcribes to the fulminating phlogiston, or the acid of the phofphoric matter, contained in the zinc, let loofe and brought into action, in the one cafe, by the heat; and, in the other, by the violent friction produced by the file. In the latter cafe he has even perceived the alliaceous or phosphoric odour; and in the dark thought he faw fome appearances of phofphoric light.

Phenomena, in many refpects fimilar, likewife attend zinc and phofphorus, when expofed to the action of water. Phofphorus evidently fuffers a fuperficial decompofition, when long kept immerged in that fluid: its furface becomes covered with a kind of powdery efflorefcence: a part of its phlogifton is feparated, and efcapes; and a part of the phofphoric acid is hereby disengaged, in a quantity fufficient to render the water fenfibly acidulous. The Author fhews that zinc, under fimilar circumftances, undergoes a fimilar decompofition: and though the change is not fo great, or fo quickly effected, yet he affirms that the water becomes milky, and at length imprelles upon the tongue a fomewhat acerb and metallic favour, precifely that of the phofphoric acid weakened or diluted.'

We omit many other points of refemblance mentioned by the Author, as well as other curious obfervations, from which be concludes that the concentrated phofphoric acid is contained even in the calx or flowers of zinc; that is, after it has loft the greatest part of its phlogifton, in the deflagration *. We apprehend

* Some curious experiments formerly made by M. Margraaf feem to confirm the Author's hypothefis. That ingenious chemist, on mixing the fal microcrcfmicus, or the fufible falt of urine, which is known to be the bafis of phofphorus, with lead and with tin, and fubjecting the mixture in clofe veffels to a violent heat, found both the metals confiderably changed; and the latter in particular con