for extruding the air will answer to about a quarter of a pound avoirdupois upon each fquare inch of furface, which is not more than an eighth part of the preffure in the regulating belly of the blowing machines at our great foundries. I think the quantity of one cubic inch per fecond is quite as much and probably more than iffues out of the blow-pipe in any course of experiment. A pair of bellows capable of extruding fomewhat more than two cubic inches at a ftroke, would confequently supply as much air as the pipe would deliver, provided the ftrokes fucceeded each other about once in two feconds, which appears to be a convenient rate of working, and by no means too quick. In very fmall bellows the internal contents may be estimated at one third of the contents of a parallelopipedon, or fquare box capable of circumfcribing the bellows when open. As a full allowance, let us fuppofe the contents of this imaginary box to be eight cubic inches, and its depth two inches. Its upper furface muft then be equal to four fuperficial inches. That is to fay, a pair of bellows fully fufficient to supply the blow-pipe will not require larger dimensions than three inches in length, one inch and a half in width, with a lift of one inch and a half for each ftroke. The fame effect may be produced by a fyringe one inch in diameter, and two inches and a half long.

The refervoir for the air may either be another pair of bellows rather larger, and difpofed to fhut by a weight or a fpring; or it may be fimply a veffel of fufficient capacity to receive the air from the bellows, and emit it in a conftant stream by virtue of its fpring under condenfation, in the fame manner as water is emitted from the air veffel of a fireengine. The emiffion of air from fuch a veffel may, in a loose way, be taken to be at half the velocity of its introduction; and, confequently, at the end of every ftroke the veffel will contain half as much more air, than the medium state of condensation, as amounts to the whole contents of the bellows; and at the beginning of every stroke, the vessel will contain half as much lefs than that quantity. From these confiderations, it appears thatthe steady stream from a fire-engine could not be produced but by two pumps alternately acting, and that the air answers scarcely any other purpose in the small air-veffels of those engines, than that of rendering the intrusion of the non-elastic water less sudden and violent. It will alfo appear from calculation, (as it does from practice, in the regulating bellies of blowing engines, on which the re-action is afforded by a variable force fomewhat refembling the fpring of the air) that a very large veffel is required to give a practical uniformity to the emitted ftream, when the action of intrufion is not conftant. Hence it appears, that an air veffel cannot be ufed to advantage, unless the bellows to our small apparatus be made double by two fixed outer boards, with valves opening inwards, and a moveable diaphragm alternating between them, and forcing the air through valves opening into one common nozle-or unlefs the fyringe, if ufed, be made to act both ways, namely, by the returning as well as by the direct ftroke. A very neat and compact apparatus for the blow-pipe might be made in this way; but it is probable that the confiderations and their advantages may be more particularly applicable to the large engines at the fmeltingworks.

XI. A fhort

A foort Account of the Life of PELLETIER. Read at the Public Sitting of the National Inflitute of France, the 15th Vendemiaire, in the Year VI. By CITIZEN LASSUS, Secretary to the Clafs of Natural Philofophy and Mathematics.

IN the courfe of the last trimestre we have had the misfortune to lofe one of our col

leagues, Bertrand Pelletier, born at Bayonne in 1761. His life was confined to the short fpace of 36 years; but his actions have left an impreffion on the minds of men which time fhall not efface.

It frequently happens that young men, fincerely defirous of instruction, have no means or place where they can be affifted in the development of their natural talents, no mafter who may point out the direct road to science, and that order and method without which the efforts of the individual too often lead him from the object of his pursuit, instead of bringing him nearer to it. This was not the case with young Pelletier. He found every advantage in his father's houfe, where he received the first elements of the art of which he was afterwards the ornament; and his fubfequent progress was made under our colleague Darcet, who having remarked in him that fagacity which may be called the inflinct of science, admitted him among the pupils attached to the chemical laboratory of the college of France. Five years of conftant application and study under fuch a master, who was himself formed by nature, perfected by experience, and affectionately disposed towards his pupil, afforded this young man a stock of knowledge very unusual at his age. He foon gave a convincing proof of this, by publishing, at the age of 21, a fet of very excellent observations on the arsenical acid. Macquer, by mixing nitre with the oxyde of arsenic, had discovered in the refidue of this operation a falt foluble in water, fufceptible of cryftallization in tetrahedral prifms, which he denominated the neutral arfenical falt. It is the arfeniate of potash. He was of opinion that no acid could decompofe it; but Pelletier showed that the fulphuric acid distilled from it does difengage the acid of arfenic. He showed the true caufe why the neutral arsenical falt is not decompofable in closed veffels, and particularly the order of affinity by which the falt itfelf is formed in the diftillation of the nitrate of potash, and the white oxyde of arfenic. He explains in what refpects this falt differs from what Macquer called the liver of arfenic. Pelletier had been anticipated in this work by Scheele, by Bergmann, by the academicians of Dijon, and by our colleague. Berthollet; but he poffeffed at least the merit, in the firft effay of his powers, of having clearly developed all the phenomena of this operation, by retaining and even determining the quantity of gas it was capable of affording. After the fame principles it was that he decompofed the arfenico-ammoniacal falt, by fhowing how, in the decompofition of this laft, the pure arfenical acid is obtained in the form of a deliquefcent glafs. In this work we may obferve the fagacity with which he was enabled to develope all the phenomena of thefe compofitions and decompofitions, by tracing those delicate threads of fcientific connection which connect the series of facts, and are imperceptible to ordinary minds.

Encouraged by the success of these first works, which he presented with the fenfibility of grateful attachment to his inftructor, he communicated his obfervations on the cryftallization of fulphur, cinnabar, and the deliquefcent falts; the examination of zeolites, particu larly the falfe zeolite of Fribourg in Brifgaw, which he found to be merely an ore of zinc; obfervations

2

observations on the dephlogisticated or oxygenated muriatic acid, relative to the absorption of oxygene; on the formation of ethers, particularly the muriatic and the acetous; and feveral memoirs on the operation of phofphorus made in the large way, its converfion into phofphoric acid, and its combination with fulphur and most metallic fubftances.

It was by his operations on that most astonishing production of chemistry, phosphorus, that he burned himself so dangerously as nearly to have loft his life. After the cure of his wound, which confined him to his bed for fix months, he immediately began the analysis of the various plumbagos of France, England, Germany, Spain, and America, and found means to give novelty and intereft to his work even after the publication of Scheele on the fame object. The analysis of the carbonate of barytes led him to make experiments on animals, which prove that this earth is a true poifon, whether it be administered in the form of the native carbonate of barytes, or whether it be taken from the decompofition of the fulphate, even though again combined with another acid.

Chemists have given the name of Strontian to a newly-discovered earth, from the name of the place where it was first found. Pelletier analysed it, and discovered it in the fulphate of barytes. He likewise analysed the verditer of England, of which painters and paper-hangers make fo much ufe. He difcovered a process for preparing it in the large way, by treating with lime the precipitate obtained from the decompofition of nitrate of copper by lime. By his process, verditer is afforded equal in beauty to that which comes from England. He was likewise one of the first chemifts who showed the poffibility of refining bell metal, and feparating the tin. His first experiments were made at Paris; after which he repaired to the foundry at Romilly to verify them in the large way. The following year he was received a member of the Academy of Sciences at Paris, and shortly afterwards went to La Fere, with our colleague Borda and General Daboville, to assist in experiments upon a new gunpowder. Being obliged, in order to render his experiments more decifive, to pass great part of the day in the open air during a cold and humid feason, his health, which was naturally delicate, became confiderably impaired. He began to recover his health, when he again became the victim of his zeal for the science he fo fuccessfully cultivated. He had nearly perished by refpiring the oxygenated muriatic acid gas. A violent attack of convulfive afthma, which returned during feveral days, was the first confequence of this unhappy accident. The diforder then feemed to abate, but it was incurable. The affiftance of art was infufficient to fave him, and he died of a pulmonary confumption in the flower of his age.

Such was the man whose premature lofs we now lament. His attachment for the fcience to which he had devoted himself, remained during the whole of his existence, and in the last moments of his life it formed an interesting object of his conversation. He poffeffed that activity of mind fo neceffary to the research of truths which are inacceffible to men of cold and languid sentiments. As a man of science, his reputation is bright and unblemished. As a citizen, his private virtues, his probity and good conduct will long continue objects of regret.

XII. Extracts

Figure, Rotation, and Projection of the Earth.

XII.

Extracts from the Systême du Monde of M. LA PLACE*.

39

THIS work of La Place explains the leading points of the fyftem of the world. It is

as it were an abstract of a large work, in which this profound geometer propofes to treat the fame objects by the principles of the moft fublime geometry, and which he promises foon to publish., I fhall copy fome of the results of this author.

"The degree meafured at the Cape of Good Hope in 37° fouth latitude †, is found to be 307999,8 feet, which is very nearly the fame as the degree of France, under the parallel of 50°, and greater than that which was measured in Pennsylvania, at the latitude of 43° 56, of which the length is no more than 307195,2 feet. The degree of the Cape is also greater than the degree measured in Italy in the latitude of 47° So, which was found to be 307680,6 feet. Nevertheless it ought to be smaller than every one of thefe degrees, if the earth were a regular folid formed by the revolution of a meridian perfectly alike on each side of the equator. Every fact leads us to conclude that this is not the cafe." Vol. I. page 105.

He concludes, that the terreftrial meridian is a line of double curvature.

"Terreftrial bodies fituated under the equator describe, by virtue of the rotation in each fecond of time, an arc of 40" 1395 of the circumference of the terrestrial equator. The radii of this equator being 19634778 feet very nearly, the verfed fine of this arc is 0,0389704 feet. Gravitation causes bodies to fall at the equator through a space of 11,23585 feet in one fecond. The central force neceflary to retain bodies at the surface of the earth, and confequently the centrifugal force arifing from its rotatory motion, is to gravity at the equator in the proportion of 1 to 288,3. The centrifugal force diminishes the weight, and bodies do not fall at the equator but by virtue of the difference of the true force. If we therefore ufe the word gravity to denote the total weight which would take place, exclusively of the diminution it undergoes, the centrifugal force at the equator is extremely nearth part of gravity. If the rotation of the earth were 17 times more rapid, the arc described in a second at the equator would be 17 times greater, and its verfed fine would be 289 times more confiderable. The centrifugal force would then be equal to gravity, and bodies would cease to prefs or weigh towards the earth at the equator." Page 263.

"To explain the double motion of rotation and progreffion in the earth, it is fufficient that the fuppofition be admitted of the primitive impulfe having been given at a small distance from its centre of gravity; which distance, supposing the planet to be homogeneous, must have been nearly the th part of its radius." Page 299.

"The probability is infinitely fmall, that the original projection of the planets, fatellites, and comets, should have paffed through their centres of gravity. All these bodies muft therefore have a rotative motion. From a fimilar reason, the fun, which turns on its axis, must have received an impulse, which not having paffed through its centre of gravity, car

Expofition du Systême du Monde, par Pierre Simon La Place, de l'Inftitut National de France et du Bureau des Longitudes, 2 vol, in 8vo. A Paris de l'Imprimerie du Cercle Social, Rue du Théâtre François, No. 4.—I have not the work, but translate from Dr. Lametherie, in the Journal de Phyfique, August 1794

The author divides the circle into 400 parts.

ries

ries it through space with the planetary fyftem, unless this motion be fuppofed to have been destroyed by an impulfe in the oppofite direction; a circumftance by no means probable.

"The impulfe given to an homogeneous fphere, in a direction which does not pafs through its centre, will caufe it to revolve conftantly round the diameter, which is perpendi cular to a plane paffing through its centre, and the line of direction of the imprefied force. New forces acting on all its parts, and of which the refult paffes through its centre, will not change the parallelifm of its axis of rotation., Thus it is that the axis of the earth remains always nearly parallel to itself in its revolution round the fun, without its being necessary to suppose, with Copernicus, an annual motion of the poles of the earth round thofe of the ecliptic.

"If the body poffefs a certain figure, its axis of rotation may change every inftant. The determination of these changes, whatever may be the forces acting on the bodies, is one of the most interesting problems of mechanics refpecting hard bodies, on account of its connection with the preceflion of the equinoxes, and the libration of the moon. The solution of this problem has led to a curious and very useful result; namely, that in all bodies there exist three axes perpendicular to each other, round which the body may turn uniformly when not folicited by external forces. On this account these axes have been called principal axes of rotation.

"A body or system of bodies, poffeffing weight, and of any figure whatever, ofcillating round a fixed and horizontal axis, forms a compound pendulum. No other pendulum exifts in nature. The fimple pendulums fo frequently treated of are pure geometrical conceptions, proper to fimplify the objects of difcuffion. It is easy to refer to these such compound pendulums as have their parts immoveably fixed together. If the length of the fimple pendulum, whofe ofcillations are ifochronous with those of the compound pendulum, be multiplied by its total mafs, and by the distance of its centre of gravity from the axis of ofcillation, the product will be equal to the sum of the products of each particle of the compound pendulum, multiplied by the fquare of its diftance from the axis. It is by means of this rule, difcovered by Huyghens, that experiments with compound pendulums have been applied to fhew the length of the fimple pendulum, which beats feconds."

The author enters into a confiderable detail refpecting the atmospheres of the planets. "In all the changes to which the atmosphere is fubject (fays he, vol. ii. p. 128.) the fum of the products of the particles of the revolving body and its atmosphere, multiplied respectively by the areas they describe round the common centre of gravity, the radii being projected on the plane of the equator, remain the fame in equal times. Suppofing, therefore, that, by any cause whatever, the atmosphere fhould become contracted, or that part thereof should become condensed on the furface of the body, the rotatory motion of the body and its atmosphere would be accelerated: for, the radii vectores of the areas de fcribed by the particles of the original atmosphere becoming fmaller, the fum of the products of all the particles, by their corresponding areas, cannot remain the fame unless the velocity be augmented.

"The atmosphere is flattened towards the poles, and fwelled out at the equator. But this oblatenefs has its limits; and in the cafe where it is greateft, the ratio of the polar and equatorial diameter is as two to three.

"The