Notice de la Vie et des Ecrits de George Louis Le Sage (English)
 THE biographical sketch here announced, has more than an ordinary claim to the attention of the reader. The subject of it is a philosopher, who, beside the peculiarities incident to genius, had several that belonged exclusively to himself. These he was careful to study and explain; and the notes which he has left behind him, seem to entitle him to the rare eulogy, of having given an accurate and candid delineation of his own character. His biographer, too, had the advantage of being intimately acquainted with the person whom he has undertaken to describe, and has been attentive to mark whatever appeared singular in the constitution or progress of his mind.
George Lewis Le Sage was born at Geneva in 1724, to which city his father, a native of France, had for some time retired, and lived by giving private lessons in mathematics and natural philosophy. The son was early initiated in these studies receiving, at the same time, in all the branches of literature, as liberal a course of education as his father's limited income would allow. A marked opposition, however, in their tastes and intellectual propensities, prevented the son from reaping from his father's instructions all the advantage that might have been expected. The old man was well informed; but his knowledge was very much confined to facts, and was accompanied with little tendency to reason, or to generalize. His son, again, even when a boy, delighted in connecting his ideas by general and abstract principles, and was not more inquisitive about facts, than about the relations in which they stood to one another. This propensity arose, in some measure at least, from the weakness of his memory, which forced him to study the most just and constant connexions among things, in order to prevent both words and ideas from escaping his recollection entirely. 'It was thus,' says M. Prevost, 'that we saw him, in his maturer years, and particularly in his old age, avoiding, with the greatest care, whatever could trouble the order of his thoughts, and substituting, with much art, a logical series of mental operations to the effort which the recollection of a single unconnected fact would necessarily have cost him'.
The history of Le Sage does indeed illustrate, in the dearest manner, the relation between the faculties of memory and abstraction, and the power which each has to supply the deficiencies  of the other. Generalization gives us a command over our ideas more complete than we can ever derive from the mere efforts of memory: It holds in its hand the clue by which this latter faculty must be guided through the labyrinth of things; and there is room to doubt, whether the power thus given to the mind is not the main source of the delight arising from abstract and philosophic speculation. Were the memory in itself to become so perfect, as to be independent of connecting principles, generalization would not be necessary, and perhaps would rarely be attempted. Two minds, both disposed to the acquisition of knowledge, could hardly be constituted with less conformity to one another, than those of Le Sage and his son. When the young man was labouring to classify his ideas, and to reduce them under general heads, the father was perpetually starting objections to his rules, and bringing forward the instances most difficult to be reduced to any general principle of arrangement. This seemed to proceed, not from any desire to embarrass or distress his son, but from a dislike which he had conceived (singular, doubtless, in a mathematician) to general methods, and to all systems whatsoever. The education, therefore, which he gave his son, was truly antiphilosophic, and certainly had no tendency to produce that love of order, system and method which characterized him through his whole life. But the mind may be constituted with some powers so weak, that discipline cannot improve them; and with others so strong, that discipline, when most perverse, cannot destroy them. Nothing could give to young Le Sage a memory nearly equal to that of ordinary men; and nothing could take from him a delight and skill in generalization, which were vastly superior.
We must not imagine from this, that the whole plan of the old man in the education of his son, was as perverse as in the case here mentioned: the information he communicated, even with so little of method and arrangement to connect the parts together, was of great value to his son, who, through his whole life, used to speak with much gratitude of his father's attention to his instruction, and of the pleasure and advantage he derived from his conversation.
The inquisitive turn of Le Sage soon displayed itself in questions, to which he did not always receive the kindest or most satisfactory answers, especially from his mother, who appears to have had none of the gentleness and patience necessary for the instruction of children. This led him to think of having recourse to trial and experience, and to interrogate nature rather than any other instructor. One of his first attempts of this sort  has been recorded in his notes, and, from the singularity of it, deserves to be remembered.
At the time we are now speaking of, the Sabbath was observed at Geneva, with a gloom and austerity of which we in Scotland can probably form a more correct notion than the inhabitants of any other country in Christendom. Le Sage felt some curiosity to know whether the Author of Nature still continued to impose on himself the same law that originally marked the institution of the day of rest. It would have puzzled the first philosopher in Europe to think of any method by which this question could be brought to the decision of experiment; but the ingenuity of our young inquirer soon suggested an expedient. He measured, with great care, the increase of a plant, day after day, in order to discover whether it would cease growing on the Sabbath. The result could not fail to solve the difficulty, and to convince the young man, that though the work of creation might terminate, the work of Providence is never interrupted. The pensive and contemplative turn of Le Sage was increased by the circumstance of his health being delicate, and his temperament too weak, to allow him to join in the fatiguing exercises which amused and occupied his companions. Great modesty, sensibility, and reserve, added, as far as his mother was concerned, to the want of comfortable society at home, condemned him almost to continual solitude, and rendered the acquisition of knowledge his only enjoyment. Thus, from circumstances apparently unfortunate, much of his intellectual excellence may be supposed to have arisen.
It is material to observe every circumstance that gave a determination to a mind that has in any thing attained celebrity; but it is very rarely that this can be done so well as in the instance we have now before us. The father of our young philosopher had but few books; and almost the only entire work on physics, which he possessed, was that of Bernard Palissy. The writings of a man who was self-instructed, -who had paid no regard to authority, when not supported by experience, -who had made valuable discoveries, and reached some very sublime and just notions concerning the structure and the revolutions of the globe, could not fail to make a strong impression on a young mind already inspired by the love of knowledge. However, though Le Sage became a great cosmologist, it does not appear that geology, of which Palissy was in some measure the founder, ever attracted much of his attention.
When he was not much more than thirteen, his father put into his hands the Antiquité Expliquée of Montfaucon, in order to excite in him a curiosity about researches into antiquity. It was the  fate of this young man, however, to derive, from the means used for his instruction, advantages very different from those that were intended, and often of far greater value. The weakness of Montfaucon's conjectures, concerning the use of many of the instruments he has described, did not escape the observation of Le Sage; and he began even then to try to establish some general and certain rules for discovering the end of a workman from the inspection of his work. Such extent of view, at so early a period of life, has rarely occurred, and must be considered as a decided mark of genius and originality. Some years after this period, connecting the pursuit just mentioned with one closely allied to it, namely, the rules that must guide us when, in the works of nature, we would trace the marks of the wise design of the Creator, he formed the idea of a treatise, entitled Teleology, and of which an account will afterwards be given.
The perusal of Lucretius is one of the events that did most determine the objects of Le Sage's researches, and indeed the whole colour and complexion of his future speculations. The precise time when this happened does not appear, though it was certainly very early, and before he had attained the age of twenty. It was then that he conceived the notion of a mechanical explanation of gravity, and of the reduction of all the motions observed in nature, to the principle of impulsion. This was suggested by the atoms of Lucretius; and the invention of a system by which such an explanation could be given, even with tolerable plausibility, must be considered as a work of great merit by all who know the difficulty with which it is attended, and its importance to philosophy. The system by which Le Sage proposed to effect this great object will be by and by considered.
Le Sage had the good fortune to study mathematics under Cramer, and philosophy under Calendrini, two eminent professors, who then adorned the University of Geneva. When it became necessary for him to make choice of a profession, he gave the preference to that of medicine. The pursuit of this study led him first to Basle, and afterwards to Paris. At the former place, he became acquainted with Daniel Bernoulli, from whom, however, his merit seems to have been completely concealed, by his awkwardness and diffidence. He says of himself, when he entered at this University: 'Ill dressed, timid, and expressing myself with difficulty, I was quite neglected in the first months of my stay, at Basle; insomuch, that they did not even think it worth while to speak French before me.' He undertook the study of the German, but the weakness of his memory din not permit him to succeed. 
The same awkwardness could not fail to have effects at Paris yet more unfavourable, as the narrowness of his income must likewise have had; yet he persevered not only in pursuing medicine, but in applying to his favourite objects in philosophy. At last he returned to Geneva; but not having the freedom of a burgess, of the city, he was refused the privilege of practising as a physician ; and saw himself, in the end, forced to relinquish every other view of fixing himself in life, but that of following the business of his father, and giving lessons in mathematics and natural philosophy. For this he appears to have been well qualified. He says of himself, that the structure of his mind was such, as had fitted him for understanding the mathematics well, but not extensively. 'Propre a bien savoir les mathematiques, mais non a en savoir beaucoup.' The first part of this assertion, we imagine, may be understood more literally than the last; though it is probably true that he was not quite master of all the modern improvements of the calculus. Some of his remarks on the state of the mathematical sciences in France, are worth attending to. In a letter to the Duke de Rochefoucault, whom he had had the honour to instruct in the mathematics, dated in 1778, he has this observation:
'In their elementary treatises of mathematics and physics, the French writers take so little trouble about the foundations of those calculations which they accumulate without end, that it seems as if they wanted to make all their pupils mere clerks in a banking house, or assistants in an observatory. They treat geometry the least geometrically possible, under the pretence that algebraic demonstrations are the shortest: as if the only object were to get to the end, and as if the road leading to it were of no importance. They are in haste to give a few notions, rather grammatical than intellectual, of the sublimer parts, before they have sufficiently developed the elements. They seem desirous of reducing astronomy, the science of motion, and chemistry, to be nothing but the humble attendants on navigation, gunnery, and the arts; as if all the world was destined for inspectors of the marine, of artillery, or manufactures; and as if the cultivation of reason was nothing in comparison with the art of getting wealth. This was not the proceeding of Descartes or Newton.' p. 272.
This character of the French Elementary writers, though, in certain respects, just, evidently has something of the air of satire, and must not be received as perfectly correct. Of too little regard to the methods of pure geometry, and too much haste to reach the more profound parts of the calculus, they may certainly be accused. But a general preference of the methods of algebra and analysis, cannot be regarded as an error, if the foundations of those methods are carefully and accurate  explained. Analytical reasonings are so much preferable to synthetical, and the art of investigation is so much more easily learned in the school of algebra than in any other, that, in a system of mathematical instruction, this latter science is undoubtedly of the first consideration. It is true, on the other hand, that the methods of analysis are not confined to algebra. Geometry has its analytical reasonings, not so extensive, nor so general, as those of algebra, but possessing a degree of simplicity and beauty that is not excelled, or rather, we think, not equalled in any other branch of science. It is a stronger proof of the neglect of geometry among the French mathematicians, than any thing that Le Sage has alleged, that in the Encyclopedie, intended to exhibit a complete picture of the knowledge of the eighteenth century, the article geometrical analysis is not to be found.
The love of accurate and precise knowledge, which Le Sage possessed eminently, probably qualified him well for a teacher of the mathematical sciences. He had several illustrious pupils, and none, certainly who does him more credit than the present professor of mathematics in the university of Geneva. M. S. L'Huilier was his relation, and was instructed by him in the science which he now professes with so much credit both to his matter and himself. He is one of the few mathematicians equally versed in the simple and elegant methods of the ancient geometry, and in the profound researches of the modern analysis. Le Sage, through his whole life, had to struggle with a feeble constitution, as well as the mental defects which have been already mentioned. He was particularly afflicted with sleeplessness, which, at times, used greatly to affect his intellectual powers, and reduce them to a Hate of extreme debility. Notwithstanding this, by employing every moment when his mind was clear and active, preserving such order and regularity as supplied the want of memory, committing every thing to writing, and having his papers in a Date of the most complete arrangement, he was able to accomplish a great deal, and to devote much time to philosophical pursuits.
His studies, however, were rendered less useful than they might have been with the originality of his turn of thinking, the precision of his knowledge and the extent of his views, by the number of objects to which he directed his attention, and by his frequent changes from one pursuit to another. Though he came back easily to the same object, yet this did not entirely make up for the what of the continued application necessary in all great undertakings. Accordingly, though few men wrote so much and so accurately, he published nothing in Lifetime but mere opuscula, and  has left few, if any, of his numerous manuscripts completely ready for the press.
One of the principal pieces which appeared in his lifetime shared the prize proposed by the Academy of Dijon in 1758, on the cause of chemical affinities. He entitled it Essai de Chimie Mechanique, and endeavoured to explain the whole of chemical action on the principle of impulse. He supposed the impelling fluid to be compared of particles of two kinds, the one greater and the other less; and he demonstrated, in virtue of the single supposition, that homogeneous bodies must attract one another more than heterogeneous. This, however, it must be conceived, comprehends but a small part of the phenomena of chemistry. If was connected with the work on gravity, which was the great business, and the favourite occupation of his life. An essay, Sur les Forces Mortes,' which he sent to the Academy of Sciences at Paris, was never published.
In the history of the same Academy for 1756, a remark is inserted from Le Sage, containing the detection of an error committed by Euclid, in the 11th book of his Elements, on the subject of solid angles. It is remarkable, that nearly about the same time, Dr Simeon of Glasgow made a similar detection, with respect to the manner in which equal solids are treated by the Greek geometer.
The tract, entitled, Lucrece Neutonien was published in the Berlin Memoirs for 1782.
Besides these, he published a few other occasional pieces, and seems to have kept up a pretty extensive correspondence with several of the first philosophers of the age. His manuscripts are, a large treatise, Sur les Corpuscules Ultramondains subordinate to which is Histoire Critique de la Pesanteur. This contains much learning, and treats of all the notions that have been entertained on the subject of gravity, and all the theories contrived for explaining it. A treatise on Cohesion, intended to show that it cannot be explained by the Newtonian attraction, is recommended by M. Prevost 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 Elastic Fluids, on General Physics, on Logic, on Moral Philosophy, and on Final Causes; also, Melanges Dystactiques, &c. Among the latter was an Essay on Punctuation, concerning which he had a system of his own; to this system he adhered rigidly; and it is said to be very philosophical; but, perhaps for that very reason, it was never come into use.
It may be thought extraordinary, that so much should have been done, and yet so little completed. The habit of continually  amassing materials, without reducing them into form, had grown on Le Sage to an excessive degree; and he urged to apologize for it by saying, ' 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 casting 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 esteem and respect wherever he was known. M. Prevost has given extracts from a number of very interesting letters, which passed between him and several of the most distinguished persons of the age: Among these are Madame Necker, the Ducheffe d'Enville, Earl Stanhope, the Duke de Rochefoucault, M. M. d' Alembert, Euler, Turgot, Boscovich, Lambert, &c.
Though his constitution was originally weak, and his health always infirm, he reached the age of eighty, and died in 1803. His biographer has given a sketch of his intellectual character, from which we shall extract a few passages.
It is impossible 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 philosopher must be numbered with those whom nature has particularly distinguished. All who knew him, were at the same time sensible of his peculiarities, 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 object for any considerable length of time; and, as he could not attend, without great difficulty, to more than one thing at the same moment, he was very easily interrupted. "I supply," said he, "the want of extent in my attention by great order and regularity; and its want of continuance, by frequently returning to the same subject." From this methodical proceeding it arose, that few men were ever more persevering than Le Sage in directing their researches to the same objects.
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 recourse to all sorts of artifices. He seized with avidity, the moments when his ideas were clearer, and his faculties most active. "I, have," says he, "extreme difficulty in connecting my thoughts, so as to make an assemblage at all supportable; and am like a painter who would work in the night, without any other illumination than what was derived from sudden and unexpected flashes of lightning" 'His method and order, in some respects, supplied so well the weakness of his memory, that, in conversation, no defect of that faculty was at all discernible. It was, accordingly, one of his constant sources of complaint, that he could not convince his friends of the badness of his memory. They who conversed with him, heard him perpetually relate, with precision, the dates, and even the most minute  circumstances, of very inconsiderable 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 consulting his repertories. '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 question, his own manuscripts afford many answers; one of the best of which is in a note, entitled, "Clef de mon Tour d' Esprit." I have been born with four dispositions well adapted for making progress in science, but with two great defects in the faculties necessary for that purpose. 1. An ardent desire to know the truth. 2. Great activity of mind. 3. An uncommon (justesse) soundness of understanding; 4. A strong desire for precision and distinctness of ideas. 5. An excessive 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 serum.
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 bas 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 principle of impulse. The causes or 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  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 satisfied. The crystalline 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 above 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 anyone 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 equal 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  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 tire 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, caeteris paribus, will be proportional to the angular pace 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 equal 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 which,  though it does not amount to a proof of a hypothesis where it is found, is an abundant reason for rejecting one, where it is wanting. The vortices of Descartes, and the ether of Newton, do neither of them give any reason why gravity should be supposed to obey one law more than another; why it should be inversely as the squares, any more than the cubes, or any other power, nay, any other function, of the distances. The extreme vagueness of such hypotheses is an unsurmountable objection to them, and, even were they true, it renders them of no use, whatsoever. Concerning a cause so imperfectly understood, we can never reason at all; and we derive, therefore, no advantage from knowing it to be true. The knowledge of the fact without the cause is just as valuable.
The above is the outline of Le Sage's theory; to follow it into all its detail, and all the variety of its applications, is a task for which we are not prepared, and one quite foreign from our purpose. It is enough, if we can in any degree awaken a curiosity which the works of the author are afterwards to gratify.
Some objections to this theory have been stated in the letters that Le Sage received from his correspondents. Boscovich, who had a system concerning the different forces which are the cause of motion, the very opposite of what has now been laid down , one in which all contact and immediate impulse are denied, could not possibly admit the theory of gravific atoms, and has stated an objection to it, which appears to us of considerable weight. The action of these atoms supposes a vast superfluity of matter, and an infinity of corpuscles, created, each, to give, at most, only a single blow, and many of them never to have any effect whatsoever. An immense multitude of atoms, thus destined to pursue their never ending journey through the infinity of space, without changing their direction, or returning to the place from which they came, is a supposition very little countenanced by the usual economy of nature. Whence is the supply of these innumerable torrents; must it not involve a perpetual exertion of creative power, infinite both in extent and in duration? The means here employed seem greater than the end, great as it is, can justify; and Le Sage must be allowed, if his system is rejected, to have had the merit of imagining a species of machinery more powerful and extensive than even the preservation of the universe can be supposed to require.
Another objection which, we understand from the author himself, had been made to his hypothesis is, that, were it true, a body enclosed on all sides ought to gravitate less to the earth, than if it were in the open air. The roof or vault over head,  would of course diminish the action of the gravific atoms that had to pass through it, and would make the body fall to the ground with less velocity than it would have done in the open air. To this it was easy to reply, that the effect here stated is real on every supposition; but is so small, that it cannot be measured in our experiments. The gravitation of a heavy body, in a room, to the roof above it, must, on the common hypothesis of attraction, diminish its weight just as much as it would be diminished by the roof's obstructing some of the gravific atoms. In both cases, the effect would be precisely the same, but too small to make any sensible diminution of the gravitation toward the great mass of the earth.
The obstruction which the gravific atoms would give to the motion of bodies, by producing a kind of resisting medium, was also objected to the doctrine of Le Sage. This might no doubt be answered, by alleging that the same effect may as well be ascribed to light, which, in this respect, is in circumstances very similar to the gravific atoms. Indeed the analogy between those atoms and the particles of light as emitted from bodies, affords the means of refuting the greater part of the objections alleged against the existence of the former. This, however, supposes that the phenomena of light are interpreted in the Newtonian manner, or by an emanation from luminous bodies. If light is considered as an elastic fluid, the vibrations of which communicate to the eye the impressions which give rise to vision, the analogy referred to has no place. Accordingly Euler, in his letters to Le Sage, observes, that this analogy had no weight with him, as he did not believe in the emanation of light. He inclines to account for gravity from the pressure of a subtle mater composing a vortex. He is not very explicit, however, and has left us much in the dark as to his opinions on this subject. His letters are, nevertheless, very interesting, particularly that dated from Berlin, 16th April 1763.
It is a good remark of Le Sage, speaking of the analogy between light and the gravific atoms, that if all bodies were transparent, so that light was never stopped in its course, it (light) would not be perceived by us, nor apprehended to exist anymore than the corpuscles to which he ascribes the cause of gravity. We are, in truth, indebted to darkness, or the absence of light, for our idea of the latter, as a separate and independent substance. Without the information thus afforded, we might, be induced by reasoning to believe that there was something necessary to vision, beside the eye and the object; but we would have no proof of its existence from immediate perception, any more than we now have of the cause of gravitation. 
Le Sage certainly did not borrow his notions concerning the cause of gravity from anyone; but he was not the first to whom such notions had occurred. Fatio de Duillier had, in some respects, anticipated the doctrine of gravific atoms; at least he had conceived a mechanical explanation of gravitation, which agreed in several particulars with that which has been described above.
The name of Fatio is well known to those who have studied the controversy between Newton and Leibniz. He was a mathematician of considerable eminence, though noted for a strange departure from the character of a philosopher, by joining himself to a set of fanatics, who carried their extravagance so far as seriously to undertake the raising of the dead. Fatio, however, never published any thing on the cause of gravitation; and his treatise on it remains still in manuscript. Mr Le Sage was first informed of this in the year 1749 by Professor Cramer, not till after his essay sur les Forces Mortes, in which he treated of this subject, was communicated to the Academy of Sciences at Paris. Le Sage left nothing undone to rescue the work of Fatio from oblivion, taking much interest in the fate of a theory founded on the same principles with his own, and invented by a man of acknowledged ability. Fatio died in England in the year 1753, in Worcestershire, at the age of ninety. His manuscripts had fallen into the hands of his neighbours, and of the people with whom he lodged. Some friends of Le Sage's, in London, had the good fortune to procure them for him. He soon after deposited them in the library at Geneva, where they still remain.
It is worth observing, that this theory of Fatio must have been known to Newton, with whom he lived in friendship, not merely from a resemblance in their philosophic, but also, as has been alleged, from an agreement in their religious sentiments. Yet it is no where hinted at by Newton, even when he is engaged in inquiries on this very subject. It is probable that he did not approve of the system of his friend, who does not appear to have had the same clear views of the matter with Le Sage, nor to have had the same ingenuity in removing the objections to his theory.
A prejudice of a very unphilosophic nature, has lately prevailed in this country, against attempts of the kind made in the writings of Le Sage. It has been represented as impious, and savouring of irreligion, to offer any physical or mechanical explanation of the force of gravity.
This, we must observe, is quite a new doctrine. Newton, who was a man of true and sincere piety, thought that he was doing nothing more inconsistent with his duty, when he was endeavouring to explain the action of gravity by that of an etherial  fluid, than when he demonstrated that the planets revolve in ellipses, and describe round their common focus areas that are proportional to the time. Dr Clarke was of the Same opinion, and has admitted, that a mechanical explanation of gravity would be of great importance in philosophy. Such an attempt is undoubtedly attended with difficulty; and perhaps we are destined to remain for ever ignorant of the cause which produces the phenomena of attraction. There can, however, be no impropriety in endeavouring, while there appear to be two kinds of causes that produce motion, to try to reduce them to one. If this is maintained to be impious, it must be on the same principle that Anaxagoras was charged with irreligion, for affirming that the planets are bodies like the earth. The same mistaken zeal has in every age opposed the same obstacles to the advancement of true philosophy.
We had almost forgot to mention the particular drift of Le Sage in the tract on the gravific atoms, which he ca1ls Lucrece Neutonien. He endeavours to show, that Epicurus, with a little attention to geometry, and the possession of no more physical knowledge than was to be found among some of his contemporaries, might have been led, by the atomical system, to the discovery of gravitation, and of the laws of the planetary motions. The tract is very ingenious and interesting.
The subject of Teleology, or the doctrine of final-causes, was one which occupied the thoughts of Le Sage, at intervals, during his whole life. Of his speculations on this subject, we are presented with a few fragments, that are in no small degree curious and interesting. The publication is by M. Reverdil, who had assisted in the composition of the work, and to whom Le Sage, in his will, left the charge of this manuscript. About the year 1740, Le Sage formed the plan of a Theory of the Ends of Nature and of Art. Wolff, who at that time taught the philosophy of Leibniz in Germany with great reputation, in his treatise on logic, recommended the theory of ENDS to be treated under the name of Teleology; and this term was adopted by Le Sage. M. Reverdil informs us, that Le Sage was confirmed in his design, by finding that some men of great celebrity had about that time conspired to combat the doctrine of final causes; some of them on a principle of universal scepticism; others to give weight to the proofs of the existence of God derived from other sources; and many, struck no doubt with the weak and childish arguments that had been often maintained on this subject. Le Sage wished to oppose all these, and in particular the latter, by showing that the theory of final causes  was not necessarily of the vague and unsatisfactory nature just alluded to.
' The greater part of the works,' says he, ' that have made their appearance on this subject, contain principles so vague and unsupported, observations so puerile and detached, and reflexions so common-place and declamatory, that it is not wonderful if they produced an effect the direct opposite of that which was intended. A theory of ENDS, or FINAL CAUSES, might be given, exempt from these great defects; embracing the objects both of nature and art; furnishing, first, rules of synthesis for the composition of a work, when the ends and means were both given; and, next, rules of analysis for discovering the intention of an artist, from the examination of his works.
M. Reverdil has given us only a few fragments from the treatise which had been drawn up conformably to this plan Those that follow will show in what manner Le Sage had endeavoured to avoid the faults which he has reprobated in others.
'A wise cause must have respect to the smallest degrees of good, because, if they are not infinitely small, the amount of the whole may be of importance; so that, if they were neglected, a considerable quantity of evil might arise.'
'There is nothing incongruous, therefore, in supposing the Divine Wisdom exercised in determining the curvature of the wing of a scarabaeus, or in planning the cells of a bee-hive. It may be true, that it imports little to the universe, whether a scarabaeus fly, with more or less ease, or a bee, employ its wax with the greatest possible frugality. It imports much, however, to the scarabaeus or the bee, and, on that account, is an object not unworthy of the attention of the Creator. If the precision in the structure of the wings or cells of these insects is useful for any purpose, however small that utility, multiplied by the number of all the scarabaei, and all the bees which have been. which are, and which are to be, may become of a considerable amount.
' When the execution of any purpose gives rife to inconvenience which admits of remedy; of all the remedies that can be applied, that is the best which rises out of the evil itself, because it is always at hand when wanted, and is sure to possess the necessary strength. Such remedies are sometime to be met with in the arts. It was thus that a hint of Monsieur the Prince of Conti, furnished Reaumur with the means of admitting the necessary quantity of air into his furnaces for hatching chickens, by making the heat of the furnace open the door of a register. The girdiron pendulum of Graham, is an instance of the same kind.
' In nature, the contraction and dilatation of the pupil of the eye, is a most remarkable instance of an inconvenience corrected by its own operation.' ' When all the accidents which happen to a work derange it; and when all those that can happen to it, have a tendency to do the  same, that work is the best possible. For it is evident, that it either cannot be improved, or that the improvement is highly improbable.
' When all the good of a system can easily be traced to general principles; and when all the evils appear to be exceptions closely connected with some good, the excess being evidently, though perhaps but in a small degree, on the side of good, the contriver must be regarded as beneficent.
' Hypothetical reasonings (whether concerning final or efficient causes) are susceptible of the highest degree of evidence when two conditions are fulfilled; when the given hypothesis explains many phenomena, and contradicts none; and when every other hypothesis is inconsistent with some of the phenomena.
' As it is very rare that one is able to reckon up all the hypotheses imaginable, in order to shew that only one of them can be received, the best philosophers, and the most scrupulous, have contented themselves with less, and have thought it sufficient if the hypothesis which they adopt explains many phenomena with precision. The more numerous the phenomena, and the greater the degree of precicion, with the more confidence do they conclude, that no other supposition will account for the appearances. It is on such a foundation as this, that the theory of gravitation is established.
On the whole, we conceive that this treatise on Teleology is written on more philosophical principles than most of those that have appeared; and we cannot but regret that it has not been given to the public entire, or with such alterations as the changes in the state of science might seem to require. The date of the MS. is 1756, and since that time, the discoveries in philosophy must have, no doubt, added considerably to the examples that might be brought to illustrate the doctrine of final causes; a doctrine which we cannot help thinking might be so treated, as to form one of the most beautiful and interesting branches of human knowledge. Indeed, we should be glad to think that more of the works of our learned and ingenious author were destined to see the light. M. Prevost, who, in the biographical sketch before us, has so judiciously consulted the reputation of his friend, and the information of the public, has it still in his power to render an important service to both.