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has left few, if any, of his numerous manuscripts completely ready for the prefs.

One of the principal pieces which appeared in his lifetime fhared the prize propofed by the Academy of Dijon in 1758, on the cause of chemical affinities. He entitled it Effai de Chimie Mechanique, and endeavoured to explain the whole of chemical action on the principle of impulfe. He fuppofed the impelling fluid to be compofed of particles of two kinds, the one greater, and the other lefs; and he demonftrated, in virtue of that fingle fuppofition, that homogeneous bodies must attract one another more than heterogeneous. This, however, it must be confeffed,, comprehends but a small part of the phenomena of chemistry. It was connected with the work on gravity, which was the great bufinefs, and the favourite occupation of his life.

An effay, Sur les Forces Mortes,' which he fent to the Academy of Sciences at Paris, was never publifhed.

In the hiftory of the fame Academy for 1756, a remark is inferted from Le Sage, containing the detection of an error committed by Euclid, in the 11th book of his Elements, on the subject of folid angles. It is remarkable, that nearly about the fame time, Dr Simfon of Glafgow made a fimilar detection, with respect to the manner in which equal folids are treated by the Greek geometer.

The tract, entitled, Lucrece Neutonien' was published in the Berlin Memoirs for 1782.

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Befides thefe, he published a few other occafional pieces, and feems to have kept up a pretty extensive correfpondence with feveral of the first philofophers of the age. His manufcripts are, a large treatife, Sur les Corpufcules Ultramondains; fubordinate to which is Hiftoire Critique de la Pefanteur. contains much learning, and treats of all the notions that have been entertained on the fubject of gravity, and all the theories contrived for explaining it. A treatife on Cohefion, intended to fhow that it cannot be explained by the Newtonian attraction, is recommended by M. Prevoft as a work of great merit, written during the full activity and vigour of the author's mind.

To these must be added the following;-on Elaftic Fluids, on General Phyfics, on Logic, on Moral Philofophy, and on Final Caufes; alfo, Melanges Dystactiques, &c. Among the latter was an Effay on Punctuation, concerning which he had a fyitem of his own; to this fyftem he adhered rigidly; and it is faid to be very philosophical; but, perhaps for that very reason, it has never come into use.

It may be thought extraordinary, that fo much fhould have been done, and yet fo little completed. The habit of continually 3

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amaffing materials, without reducing them into form, had grown on Le Sage to an exceffive degree; and he used to apologize for it by faying, that as long as he could find any thing new to put on paper, he grudged the time that must be employed in polishing old materials, or cafting them over again.'

The ingenuity of his mind, and the original turn of his thoughts, added to a character of great probity and worth, procured him efteem and respect wherever he was known. M. Prevoft has given extracts from a number of very interefting letters, which paffed between him and feveral of the moft diftinguished perfons of the age: Among these are Madame Necker, the Ducheffe d'Enville, Earl Stanhope, the Duke de Rochefoucault, M. M. d'Alembert, Euler, Turgot, Bofcovich, Lambert, &c.

Though his conftitution was originally weak, and his health always infirm, he reached the age of eighty, and died in 1803. His biographer has given a fketch of his intellectual character, from which we shall extract a few paffages.

It is impoffible not to recognize, in the works of Le Sage, and his manner of thinking, a strong character of originality; and, if a cautious and regulated invention be characteristic of genius, this philofopher must be numbered with thofe whom nature has particularly diftinguished. All who knew him, were at the fame time fenfible of his peculiarties, which he himself did not indeed attempt to conceal, but endeavoured to explain. He acknowledged that two of his faculties were weak,-attention and memory. He was unable to fix the former on one objec

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any confiderable length of time; and, as he could not attend, without great difficulty, to more than one thing at the fame moment, he was very easily interrupted. "I fupply," faid he, "the want of extent in my attention by great order and regularity; and its want of continuance, by frequently returning to the fame fubject. From this methodical proceeding it arofe, that few men were ever more perfevering than Le Sage in directing their refearches to the fame objects.

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His memory was unmanageable and capricious in a high degree. He had no power over it; and, in order to direct it, was obliged to have recourfe to all forts of artifices. He feized, with avidity, the moments when his ideas were cleareft, and his faculties moft active. "I have," fays he, "extreme difficulty in connecting my thoughts, fo as to make an affemblage at all fupportable; and am like a painter who would work in the night, without any other illumination than what was derived from fudden and unexpected flashes of lightning.

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• His method and order, in fome refpects, fupplied fo well the weakness of his memory, that, in converfation, no defect of that faculty was at all difcernible. It was, accordingly, one of his conЯtant fources of complaint, that he could not convince his friends of the, badness of his memory. They who converfed with him, heard him perpetually relate, with precifion, the dates, and even the moft minute circumftances,

circumstances, of very inconfiderable events. They believed his memory to be tenacious; whereas, the truth was, that he kept notes of every thing, and was every now and then confulting his repertories.

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Such being the weakness of his intellectual organization, he often asked himself, how he had ever been able to do any thing at all? To this queftion, his own manfucripts afford many anfwers; one of the best of which is in a note, entitled, " Clef de Mon Tour-d'Esprit. I have been born with four difpofitions well adapted for making progrefs in science, but with two great defects in the faculties neceffary for that purpofe. 1. An ardent defire to know the truth. 2. Great activity of mind. 3. An uncommon (jufteffe) foundness of understanding. 4. A ftrong defire for precifion and diftin&tnefs of ideas. 5. An exceffive weakness of memory. 6. A great incapacity of continued attention. '

By using the resources which nature had bestowed, and compensating, by much skill and labour, the want of the qualities she withheld, he was able to make no small progress even as an inventor in science. He used to apply to himself the saying of Bacon,-Claudum in via cursorem extra viam antevertere. ̧

One of the principal causes that retarded the publication of his works, was the difficulty of making his favourite system be relished in the scientific world. The conviction which he himself had of its truth, and the complete persuasion that it must ultimately prevail, could not prevent him from perceiving, that though all acknowledged the ingenuity, yet few were prepared to admit the truth of his theory. He was perfectly aware, that his own way of thinking on this, as well as many other subjects, was peculiar, and not readily adopted by other men.

This is strongly marked by the title of one of his parcels of notes; On the immiscibility of my thoughts with those of others.' He has investigated, in his usual way, the causes of this immiscibility, and has divided his readers into different classes, according to their greater or less fitness to judge of the principles of his philosophy. He has applied to himself a line. of Ovid, with much truth

Non ego cessavi, nec fecit inertia sèrum.

Without entering on this discussion, we shall endeavour to give the best idea we can of the system so often mentioned, as far as we have been able to collect it from his letters, and from the very ingenious tract, Lucrece Neutonien, which Mr Prevost has introduced into his Appendix.

The object of this system was to explain the law of gravity, both as it prevails on the earth and in the heavens, by the princi ple of impulse. The causes of all the motions we perceive in the material world, may be reduced to three-Impulse, Attraction, and Repulsion. Impulse acts by contact; one moving body communicates motion to another body; and the rule by which this VOL. X. NO. 19.

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change is produced, is, that the motion communicated in any given direction, and that which is lost in the same direction, are precisely equal. The motions that we ourselves impress on the bodies around us, are of this nature.

Again, when a stone falls to the ground, or when iron approaches a magnet, motion is produced without contact; both the bodies acquire motions which are equal, but in opposite directions. The motions ascribed to repulsion are of the same kind with these last, in as much as there' is no contact, and as the motions acquired in opposite directions are equal. The only difference is, that the bodies, instead of approaching, recede from one another. Whether attraction and repulsion may not be regarded as one and the same law, acting under different circumstances, we do not at present inquire: the object of Le Sage was to reduce them both to impulse; and, could this be done, it would no doubt be a great advance in science, and we might seem, in one quarter at least, to have pushed our researches to their legitimate and proper termination. Our idea of the communication of motion by impulse, is not without difficulty; but it is clearer and more familiar to us than any other, and is that with which the mind is most disposed to remain satisfiedi

The chrystalline spheres of the ancients may be regarded as the first attempt to explain the motion of the heavenly bodies by impulse; the vortices of Descartes is the next ; the ether of Newton is the third. The first is known to be without foundation ; the second is a vague and gratuitous supposition; and the third is, at best, far from being satisfactory.

Le Sage has certainly been more fortunate than any of his predecessors; and his hypothesis has this undoubted superiority a bove all the others that have been proposed for explaining gravitation, that it assigns a satisfactory reason why that force varies inversely as the square of the distance.

Suppose that, through any one point of space, innumerable straight lines are drawn in all different directions, each making a very small angle with those that are nearest it; and let a torrent of particles, or indivisible atoms, move continually in a direction parallel to each of these lines, the section of each torrent, in a transverse direction to its motion, being e qual to the section of the sensible world in the same direction. Thus, there will be an indefinite number of torrents of atoms * intersecting one another in every possible direction, much like the streams of light which issue from all the points of the surface of a luminous body. The analogy between the emanation of light and the motion of those corpuscles, is so close, that an imagination which is familiar with the one, will not experience

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much difficulty in becoming familiar with the other. Like light, also, the atoms, of which these torrents are composed, must be supposed to move with inconceivable rapidity, and to be of such extreme minuteness, that, though flowing continually in all directions, they do not obstruct or interfere with the motions of one another.

If, now, it be supposed that these atoms are unable to penetrate the solid and indivisible particles of bodies, and, when they enter bodies, can only pass through the intervals or vacuities between their particles, it is evident that they must strike against those particles, and must therefore communicate a certain degree of motion to them, or to the bodies of which they are composed.

If, then, there were but a single body in the universe, with whatever force the torrents of atoms struck against its particles, the body would remain at rest, the impulses in opposite directions being perfectly equal. But if there be two bodies; then, since each of them, by intercepting a part of the atoms of the torrents, will shelter the other from the action of so much force, it is evident that the bodies will be both impelled toward one another, and that each of them will receive fewer shocks on the side where the other body is, than on the opposite. Further, if we suppose the bodies spherical, the intensity of this force, cateris paribus, will be proportional to the angular space included within a cone, which has for either base the transverse section of the bodies. Now, it is easy to prove that this angular space is proportional to the square of the distance of the bodies inversely. Therefore, the force with which the bodies will be urged toward one another, will be inversely as the square of the distance, which is the law followed by gravity.

This will be true if the bodies are equai in quantity of matter, so as to intercept equal quantities of the atoms. But if their quantities of matter are unequal, then, at an average of all the chances, each will intercept a number of particles proportional to its quantity of matter, and so the forces with which the bodies are impelled toward one another, will be as the quantity of matter directly, and the square of the distance inversely. This is precisely the law of gravitation; and the particles by which this effect is brought about, are called by Le Sage the gravific, or the ultramundane atoms.

This hypothesis, as already observed, must be confessed to Have done what no other attempt to account for gravity can boast of, that is, to have assigned a reason why that force is inversely as the square of the distance, and directly as the quantity of matter. It has, then, the precision which belongs to truth, and

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