Charles Bossut on Leibniz and Newton

The productions of genius being of an order infinitely superior to all other objects of human ambition, we need not be surprised at the warmth with which Leibniz and Newton disputed the discovery of the new geometry. These two illustrious rivals, or rather Germany and England, contended in some respects for the empire of science.

The first spark of the war was excited by Nicholas Facio de Duillier, a Genevese retired to England; the same who afterwards exhibited a strange instance of madness, by attempting publicly to resuscitate a dead body in St Paul’s church, but who was at that time in his sound senses, and enjoyed some reputation among geometricians. Urged on the one hand by the English, and on the other by personal resentment against Leibniz, from whom he professed not to have received the marks of esteem he conceived to be his due, he thought proper to say, in a little tract ‘on the curve of swiftest descent and the solid of least resistance,’ which appeared in 1699, that Newton was the first inventor of the new calculus; and that he said this for the sake of truth and his own conscience; and that he left to others the task of determining what Leibniz, the second inventor, had borrowed from the English geometrician.

Leibniz, justly feeling himself hurt by this priority of invention ascribed to Newton, and the consequence maliciously insinuated, answered with great moderation, that Facio no doubt spoke solely on his own authority; that he could not believe it was with Newton’s approbation; that he would not enter into any dispute with that celebrated man, for whom he had the profoundest veneration, as he had shown on all occasions; that, when they when they had both coincided in some geometrical inventions, Newton himself had declared in his Principia that neither had borrowed anything from the other; that, when he published his differential calculus in 1884, he had been master of it about eight years; that about the same time, it was true, Newton had informed him, but without any explanation, of his knowing how to draw tangents by a general method, which was not impeded by irrational quantities; but that he could not judge whether this method were the differential calculus since Huygens, who at that time was unacquainted with this calculus, equally affirmed himself to be in possession of a method which had the same advantages; that the work of an English writer, in which the calculus was explained in a positive manner was the preface to Wallis’s Algebra, not published till 1693; that, relying on all these circumstances, he appealed entirely to the testimony and candour of Newton, etc.

The assertion of Facio, being altogether destitute of proof, was forgotten for several years. In 1708, Keil, perhaps excited by Newton, or at last secure of not being disavowed by him, renewed the same accusation. Leibniz observed that Keil, whom he notwithstanding termed alearned man, was too young to pass a decided judgement on things that had occurred several years before; and he repeated what he had before said, that had occurred several years before; and he repeated what had been said that he rested on the candour and justice of Newton himself. Keil returned the charge; and in 1711, in a letter to Sir Hans Sloane, secretary to the Royal Society, he was not contented with saying that Newton was the first inventor; but plainly intimated that Leibniz, after having taken his method from Newton’s writings, had appropriated it to himself, merely employing a different notation; which was charging him in other words with plagiarism.

Leibniz, indignant at such an accusation, complained loudly to the Royal Society; and openly required it to suppress the clamours of an inconsiderate man who attacked his fame and his honour. The Royal Society appointed a committee to examine all the writings that related to this question; and in 1712 it published these writings, with the report of the committee, under the following title: Commercium epistolicum de Analysi promota. Without being absolutely affirmative, the conclusion of the report is that Keil had not calumniated Leibniz. The work was dispersed over all Europe with profusion.

Newton was at that time president of the Royal Society where he enjoyed the highest respect and most ample power; perhaps therefore delicacy should have induced him to lay the cause before another tribunal. It is true that Fontenelle has said, in his eulogy of Leibniz, that ‘Newton did not appear in the business, but left the care of his glory to his countrymen, who were sufficiently zealous.’ Leibniz, however, was dead and Newton living when he said this: and no doubt he had been deceived by false documents, for in the course of the dispute Newton wrote two very sharp letters against Leibniz in which we may be a little surprised to perceive too much art and ingenuity employed for the purpose of revoking or weakening the testimonies of high esteem which he had formerly expressed for him on different occasions, particularly in the celebrated scholia to the 7th proposition of the 2nd book of the Principia.

It appears that the Royal Society, while it hastened the publication of the documents that made against Leibniz, without waiting for those which he promised in his defence, was sensible that it would be accused of partiality or precipitation: for it took care soon after to declare that it had no intention of passing judgment on the cause, but left all the world at liberty to discuss it and give it’s opinion. I beg leave, therefore, to go into this examination to which I will pay all attention in my power. To me Leibniz and Newton are both indifferent: I have received from neither of them, if I may use an expression of Tacitus, either benefit or injury. The sublime genius of both demands profound homage; but it is incumbent on us still more to respect the truth.

Newton, gifted by nature with superior intellect, was born at a time when Harriot, Wren, Wallis, Barrow, and others, had already rendered the mathematical sciences flourishing in England, enjoyed likewise the advantage of receiving lessons from Barrow in his early youth at Cambridge. The whole bent of his genius was toward studies of this kind, and the success he obtained was prodigious. Fontenelle has applied to him what Lucan said of the Nile: that mankind had not been permitted to see his feeble beginnings. It is affirmed that he laid the foundations of the grand theories, by which he afterwards obtained so much fame, at the age of twenty-five.

Leibniz, who was four years younger, found but moderate assistance in his studies in Germany. He formed himself alone. His vast and devouring genius, aided by an extraordinary memory, took in every branch of human knowledge; literature, history, poetry, the law of nations, the mathematical sciences, natural philosophy, etc. This multiplicity of pursuits necessarily checked the rapidity of his progress in each; and accordingly he did not appear as a great mathematician till seven or eight years after Newton.

Both these great men were in possession of the new analysis long before they made it known to the world. If priority of publication determined priority of discovery, Leibniz would have completely gained his cause: but this is not sufficient on the present occasion to enable us to pronounce with confidence. The inventor may have long kept the secret to himself; he may have allowed some hints to escape him on which another may have seized. If possible, therefore, let us trace it to it’s source and endeavour to discover the beneficent being who, to adopt the fine simile of Fontenelle, like Prometheus in the fable stole fire from the gods to impart it to mankind.

The Commercium epistolicum contains in the first place, to date from the year 1669, several analytical discoveries of Newton. In the piece entitled De Analysi per Aequationes Numero Terminorum infinitas besides the method for resolving equations by approximation, which has nothing to do with us here, Newton teaches how to square curves, the ordinates of which are expressed by monomials or sums of monomials; and when the ordinates contain complex radicals, he reduces the question to the former case by evolving the ordinate into an infinite series of simple terms by means of the binomial theorem, which no one had done before. Sluze and Gregory had each separately found a method for tangents; and Newton, in a letter to Collins dated December the 10th, 1672, proves that he had likewise found one; he applies it to an example without adding the demonstration; and he afterwards says that it is only a corollary of another general method which he has for drawing tangents, squaring curves, finding their lengths and centres of gravity, etc., without being stopped by the radical quantities, as Hudde was in his method for maxima and minima.

In these two writings of Newton the English have clearly perceived the method of fluxions; after it had been made known throughout Europe, however, by the writings of Leibniz and the two Bernoullis: but the geometricians of other countries have not seen with exactly the same eyes. While they agree that the evolution of radicals into series is a considerable step made by Newton, they immediately perceive, without the assistance of any subsequent and conjectural light, that the methods of Fermat, Wallis, and Barrow, might have been employed to find the results concerning quadratures which Newton contents himself with enunciating; since, after the evolution of radicals, if there be any, nothing more is necessary but to sum up the monomial quantities. They confess that the two pieces in question contain a vague indication of the method of fluxions, if you will: an indication perhaps sufficient to show that Newton was then in possession of the first principles of the method; but too obscure to make the reader at all acquainted with it.

What renders this conjecture very probable is that Mr Oldenburg, secretary to the Royal Society, sending a copy of Sluze’s Method of Tangents, which had been printed at London, to the author on the 10th of July 1673, encloses him an extract from a letter of Newton’s; in which, after having observed that this method justly belongs to Sluze, Newton goes on thus: ‘as to the methods,’ (he is speaking of that of Sluze and his own) ‘they are the same, though I believe they are derived from different principles. I know not, however, whether the principles of Mr Sluze be as fertile as mine, which extends to the affected equations of irrational terms, without it’s being necessary to change their form.’ If he had then possessed the method of fluxions in such an advanced state as has since been pretended, would he not have spoken with so much reserve, instead of saying plainly that the method of Sluze and that of fluxions were different? Will it be supposed that he expressed himself thus out of modesty? Surely the truth may be spoken without any infringement of the laws of modesty, even when it is to our own advantage.

All these considerations appear to me to evince that, if the piece De Analysi per Aequationes and the letter of 1672 contain the method of fluxions, it was at least enveloped in great darkness. But whether it were or not, I shall proceed to demonstrate that Leibniz either had no knowledge of these two pieces before he discovered his differential calculus, or derived no information from them. This is an important point which his defenders have not sufficiently established and on which I hope to leave no doubt remaining.

In 1672 Leibniz quitted the universities of Germany and came to France, where he was chiefly occupied in the study of the law of nations and history. He was already initiated into mathematics, however, as in 1666 he had published a little tract on some properties of numbers. In the beginning of 1673 he went to London where he saw Oldenburg, with whom he commenced an epistolary correspondence. In one of his letters to Oldenburg, written even while he was in London, Leibniz says that having discovered a method of summing up certain series by means of their differences, this method was shown to him already published in a book by Mouton, canon of St Paul’s at Lyon, ‘On the Diameters of the Sun and Moon:’ that he then invented another method, which he explains, of forming the differences and thence deducing the sums of the series: that he is capable of summing up a series of fractions of which the numerators are unity and the denominators either the terms of the series of natural numbers, those of the series of triangular numbers, or those of the series of pyramidal numbers, etc. All these researches are ingenious and seem to have at least a remote relation to the calculus of differences. The English have never asserted, and at any rate there exists not the least proof, that Leibniz had seen the two pieces by Newton abovementioned during this first visit to England.

After staying some months in London, Leibniz returned to Paris where he formed an acquaintance with Huygens, who laid open to him the sanctuary of the profoundest geometry. He soon found the approximate quadrature of the circle by a series analogous to that which Mercator had given for the approximate quadrature of the hyperbola. This series he communicated to Huygens by whom it was highly applauded; and to Oldenburg, who answered him that Newton had already invented similar things not only for the circle but for other curves of which he sent him sketches. In fact the theory of series was already far advanced in England at that time; and though Leibniz had likewise penetrated deeply into it, he always acknowledged that the English, and Newton in particular, had preceded and surpassed him in that branch of analysis: but this is not the differential calculus, and the English have shown too evident a partiality in their endeavours to connect these two objects together,

Let us hear and examine the history which Leibniz gives of his discovery of the differential calculus. He relates that, on combining his old remarks on the differences of numbers with his recent meditations on geometry, he hit upon this calculus about the year 1676; that he made astonishing applications of it to geometry; that being obliged to return to Hanover about the same time he could not entirely follow the thread of his meditations; that endeavouring nevertheless to bring forward his new discovery, he went by the way of England and Holland; that he stayed some days in London where he became acquainted with Collins who showed him several letters from Gregory, Newton, and other mathematicians, which turned chiefly on series.

According to this account, it would appear that Leibniz, wishing to spread abroad his new discovery, must then have made known in England the differential calculus. Let us add that in a letter from Collins to Newton, dated the 5th of March 1677, it is said that Leibniz, having spent a week in London in October 1676, had put into Collin’s hands some papers [This passage and several other large fragments of the same letter were suppressed in theCommercium epistolicum], of which extracts or copies should be sent to Newton immediately. Collins says nothing of the nature of these papers, and we find no trace of them in the Commercium epistolicum. But if the account given by Leibniz be just, or if his memory did not deceive him, when he said he was in possession of the differential calculus before his second visit to England, no doubt some private reason then occurred to induce him to keep his discovery secret, contrary to the design he had first formed of bringing it forward: for in this very letter Collins mentions another from Leibniz to Oldenburg written from Amsterdam the 28th of November 1676 in which Leibniz proposes the construction of tables of formulas tending to improve the method of Sluze, instead of explaining the differential calculus or at least pointing it out as much more expeditious and more convenient. The English therefore are justified in saying that Leibniz, when he passed through London in 1676, did not teach them the differential calculus: but they ought to acknowledge that the same letter conclusively proves that he likewise learnt nothing from them on the subject. In fact if, as has been asserted since, a knowledge of the method of fluxions had then been imparted to him, must he not have been out of his senses to propose a month after to the secretary of the Royal Society, a man of great skill in these matters, means of improving the method of Sluze itself, without saying a single word of another method much more simple which had just been taught him in England?

Thus I believe I may decidedly conclude either that Leibniz did not see the work De Analysiand Newton’s letter when he was in England in October 1676; or, if he did see them, that he derived no assistance from them any more than the learned geometricians of England who had had all that time to mediate on them, and besides were at hand to apply to the author for every necessary illustration. The English have never formally declared that he had seen the book De Analysi; they content themselves with positively asserting that he had seen the letter of 1672. But supposing this to be true, we can draw no inference against Leibniz from it; for beside that the letter contains only results, without any demonstration, it is not very clear that it indicates a method essentially different from that of Sluze as the reader may have remarked from Newton’s words already quoted.

In the whole of this business there are but three pieces truly decisive; first, a letter from Newton to Oldenburg dated the 24th of October 1676 which was communicated to Leibniz the year following: second, the answer which Leibniz returned to Oldenburg respecting this letter, June the 21st, 1677: third, the scholia to Newton’s Principia already quoted, published towards the end of 1686. Let us briefly analyse these three pieces.

Newton’s letter, exclusive of different researches concerning series which are here to be left out of the question, contains several theorems that have the method of fluxions for their basis, but the author keeps his demonstrations secret. He contents himself with saying that he has deduced them from the solution of a general problem which he expresses enigmatically by transposing the letters and the sense of which, as explained after the business was known, is ‘an equation containing flowing quantities being given, to find fluxions and inversely.’ What light could Leibniz derive from such an anagram? All we can conclude from such a letter is that at the time it was written Newton was in possession of the method of fluxions; by which, however, is to be understood simply the method of tangents and quadratures; for the method of resolving differential equations was then out of the question, this not being invented till long after as has been said above.

Leibniz, in his letter to Oldenburg, begins with saying that he, as well as Newton, had found Sluze’s method for tangents to be imperfect. Then he explains openly and without mystery that of the differential calculus, affirming that he had long employed it for drawing the tangents of curve lines. Here then we have the clear and positive solution of the problem, the possession of which Newton so carefully endeavoured to reserve to himself.

The scholia to the Principia says as follows: ‘In a correspondence in which I was engaged with the very learned geometrician Mr Leibniz ten years ago [through the medium of Oldenburg], having informed him that I was acquainted with a method of determining the maxima and minima, drawing tangents, and doing other similar things, which succeeded equally in rational equations and radical quantities, and having concealed this method by transposing the letters of the words which signify: ‘an equation containing any number of flowing quantities being given, to find fluxions and inversely’: that celebrated gentleman answered that he had found a similar method; and this, which he communicated to me differed from mine only in the enunciation and notation.’ To this the edition of 1714 adds: ‘and in the idea of the generation of quantities.’ Is it possible to say more expressly that Leibniz separately invented the method of fluxions and that he had communicated it frankly without involving himself in mystery like Newton?

From these three pieces therefore it is clear that if Newton first invented the method of fluxions, as is pretended to be proved by his letter of the 10th of December 1672, Leibniz equally invented it on his part, without borrowing anything from his rival. These two great men by the strength of their genius arrived at the same discovery through different paths; one by considering fluxions as the simple relations of quantities which rise or vanish at the same instant; the other by reflecting that in a series of quantities which increase or decrease, the difference between two consecutive terms may become infinitely small, that is to say, less than any determinable finite magnitude.

This opinion, at present universally received except in England, was that of Newton himself when he first published his Principia, as we see from the extract given above. At that time the truth was near it’s source and not yet altered by the passions. In vain did Newton afterwards change his language, led away by the flattery of his countrymen and disciples; in vain did he pretend that the glory of a discovery belongs entirely to the first inventor, and that second inventors ought not to be admitted to share it. In the first place, without discussing his pretended priority, it was replied that two men, who separately make the same important discovery, have an equal claim to admiration; and that he who first makes it public has the first claim to the public gratitude. It was then proved to him that even his own principle did not justly apply here.

The design of stripping Leibniz and making him pass for a plagiary was carried so far in England that during the height of the dispute it was said (and Newton himself was not ashamed to support the objection) that the differential calculus of Leibniz was nothing more than the method of Barrow. What are you thinking of, answered Leibniz, to bring such a charge against me? Will you have the differential calculus to be nothing but the method of Barrow when I claim it? and at the same time say it was invented by Mr Newton when you wish to rob me of it? Can you be so blinded by passion as not to perceive this manifest contradiction? If the differential calculus were really the method of barrow (which you well know it is not), who would most deserve to be called a plagiary? Mr Newton, who was a pupil and friend of Barrow and had the opportunities of gathering from his conversation ideas which are not in his works? or I who could be instructed only by his works and never had any acquaintance with the author?

Johann Bernoulli, who in concert with his brother learned the analysis of infinities from the writings of Leibniz, opposed to the Commercium epistolicum a letter where he advances not only that the method of fluxions did not precede the differential calculus but that it might have originated from it; and that Newton had not reduced it to general analytical operations in form of an algorithm till the differential calculus was already disseminated though all the journals of Holland and Germany. His reasons are in substance, first, the Commercium epistolicumexhibits no vestige of Newton’s having employed dotted letters to denote fluxions in the writings alleged; secondly, in the Principia, where the author had so frequently occasion for employing this calculus and giving it’s algorithm, he has not done it; he proceeds everywhere by means of lines and figures without any determinate analysis, and simply in the manner of Huygens, Roberval, Cavalleri, etc,: thirdy, the dotted letters first began to appear in the third volume of Wallis’s Works, several years after the differential calculus was everywhere known; fourthly, the true method of differencing differences, or of taking the fluxions of fluxions, was unknown to Newton, since even in his treatise on quadratures, not published till 1704, the rule he gives at the end for determining the fluxions of all orders by considering these fluxions as the terms of the power of a binomial formed of a variable quantity, and it’s first fluxion, and treating the first fluxion as constant, is false except simply for the term which answers to the first fluxion: fifthly, at the same period of 1704 Newton was not versed in the integral calculus of differential equations which Leibniz and the two Bernoullis had already carried so far; otherwise he would not have failed to treat this part of the analysis of infinities, the most difficult, and at least as worthy of being promulgated and carried to perfection as the quadratures on which he enlarged so much.

To this letter the English answered that the notation did not constitute the method: that the principles of the calculus of fluxions were contained in Newton’s great work and in his letters: that the rule in the treatise on quadratures for finding the fluxions of all orders was true, suppressing the denominators of the terms of the series and gave by consequence quantities proportional to the true fluxions. I do not find that they gave any answer to the last objection.

The partisans of Leibniz replied that the advantages of an analytic method depend in great measure on the simplicity of the algorithm: that the Characteristic of Leibniz had already occasioned the new analysis to make immense progress at a time when scarcely anyone had heard of Newton’s book: that it was in vain to endeavour to deny or palliate the erroneousness of Newton’s rule for finding the fluxions of all orders: and that it could not be said that the terms of a seris of fractions were proportional to the terms of another series of fractions when the corresponding terms had different denominators, as was the case here.

Such were the reasons alleged and contested between the two parties for more than four years. The death of Leibniz, which happened in 1716, it may be supposed, should have put an end to the dispute: but the English, pursuing even the manes of that great man, published in 1726 an edition of the Principia in which the scolium relating to Leibniz was omitted. This was confessing his discovery in a very authentic and awkward manner. Must they not be aware that the chimerical design of annihilating the testimony, which an honourable emulation had formerly rendered to truth, would be ascribed to national prejudice or to a sentiment even more unjust?

In later times there have been geometricians who, without taking a decided part between Newton and Leibniz, have objected to the latter, that the metaphysics of his method were obscure, or even defective; that there are no quantities infinitely small; and that there remain doubts concerning the accuracy of a method into which such quantities are introduced.

But Leibniz might answer: ‘I have proposed the existence of infinitely small quantities only as subsidiary, or as a simple hypothesis, serving to abridge the calculus and reasonings on which it is founded. I have no need for the existence of infinitely small quantities: it is enough for my purpose, as I have said in several of my works, that the differences are less than any finite quantity you please to assign; and consequently the error which may result from my supposition is less than any determinable error, which is the same as absolutely nothing. The manner in which Archimedes demonstrates the proportion of the sphere to the cylinder has a similar principle for it’s basis. Mr de Fontenelle, who however meant me well, was wrong when he contented himself with saying at the beginning of his Géométrie de l’Infini, that, after having at first admitted infinitely small quantities, I had at length receded so far as to reduce the infinities of different orders to mere incomparables in the sense in which a grain of sand would be incomparable to the globe of the Earth. He should have added that I use this similitude only for the purpose of presenting a general and sensible idea of my differences to the imagination of certain readers; and that in the paper to which he alludes, I conclude with remarking expressly that instead of an infinitely large or small quantity, quantities should be assumed as large or as small as is necessary to render the error less than a given error. The metaphysics of my calculation, therefore, are perfectly conformable to those of the method of exhaustion of the ancients, the certainty of which has never been questioned by anyone; and whatever may have been urged in this respect my rival has no real advantage over me.

Lastly it has been said that, notwithstanding Newton’s affection of employing synthesis alone in his Principia, at present it cannot be doubted that he discovered a great number of propositions by the analytic method of fluxions: that this application of it to multitude of objects so important implies a long series of meditation: and that at least, according to all appearance, he must have been in possession of the method of fluxions before Leibniz, for he must have spent many years in writing his book. Let us examine the consequences to be drawn from this induction.

Perhaps there never existed a man more highly endowed than Newton with that strength of intellect and vigour of mind which are capable of conceiving, pursuing, and executing a vast design. Leibniz has published no single work that can be compared with the Principia for importance and connection of subject. Too much carried away by the vivacity of his genius, and the multitude and variety of his occupations, journeys, and literary correspondence with most of the learned in all parts of the World, he could not confine himself to delving long at one subject, or pursuing in detail all the consequences of a grand principle: but the Collection of his Works, and his Epistolary Correspondence with Johann Bernoulli, bear in every part the strongest marks of invention. Everywhere he disseminates new ideas, and germs of theories, the development of which would sometimes produce whole treatises. He has the advantage over Newton of having invented and carried to a great length the integral calculus of differential equations. If he be not equally profound with the English geometrician, he appears to surpass him in that rapid penetration and sharpness of intellect which seize on the most subtle and striking questions in any subject. The one has left us a greater mass of geometrical truths: the other more accelerated the progress of science in his time by the simple and commodious notation of his calculus, the applications he made of it himself, or enabled others of the learned to make, the encouragements he gave them, and the new paths he was continually opening to their meditations. To conclude, whatever length of time the completion of the Principia may have required, we ought not to forget that this work did not appear till two or three years after Leibniz had published his differential calculus, and some sketches of the integral.