ALEMBERT, Jean le Rond d’, an eminent French philosopher, was born at Paris in 1717. He derived the name of Jean le Rond from that of the church near which, after his birth, he was exposed as a foundling. His father, informed of this circumstance, listened to the voice of nature and duty, took measures for the proper education of his child, and for his future subsistence in a state of ease and independence.

He received his first education in the College of the Four Nations, among the Jansenists, where he gave early marks of capacity and genius. In the first year of his philosophical studies he composed a Commentary on the Epistle of St Paul to the Romans. The Jansenists considered this production as an omen that portended to the party of Port-Royal a restoration to some part of their ancient splendour, and hoped to find one day in Μ. d’Alembert a second Pascal. To render this resemblance more complete, they engaged their rising pupil in the study of the mathematics; but they soon perceived that his growing attachment to this science was likely to disappoint the hopes they had formed with respect to his future destination: they therefore endeavoured to divert him from this line; but their endeavours were fruitless.

On his leaving college, he found himself alone and unconnected with the world; and sought an asylum in the house of his nurse. He comforted himself with the hope that his fortune, though not ample, would better the condition and subsistence of that family, which was the only one that he could consider as his own. Here, therefore, he took up his residence, resolving to apply himself entirely to the study of geometry; and here he lived, during the space of forty years, with the greatest simplicity, discovering the augmentation of his means only by increasing displays of his beneficence, concealing his growing reputation and celebrity from these honest people, and making their plain and uncouth manners the subject of good-natured pleasantry and philosophical observation. His good nurse perceived his ardent activity, heard him mentioned as the writer of many books, but never took it into her head that he was a great man, and rather beheld him with a kind of compassion. “ You will never," said she to him one day, “ beany thing but a philosopher — and what is a philosopher ? — a fool, who toils and plagues himself during his life, that people may talk of him when he is NO MORE.”

As Μ. d’Alembert’s fortune did not far exceed the demands of necessity, his friends advised him to think of a profession that might enable him to augment it. He aocordingly turned his views to the law, and took his degrees in thst line; but soon abandoned this plan, and applied to the study of medicine. Geometry, however, was always drawing him back to his former pursuits; and after many ineffectual efforts to resist its attractions, he renounced all views of a lucrative profession, and give himself over entirely to mathematics and poverty.

In the year 1741 he was admitted member of the Academy of Sciences; for which distinguished literary promotion, at such an early age, he ħad prepared the way by correcting the errors of a celebrated work,^[1. The Analyse Démontrée of F. Beniau. ] which was deemed classical in France in the line of geometry. He afterwards set himself to examine, with deep attention and assiduity, what must be the motion of a body which passes from one fluid into another more dense, in a direction not perpendicular to the surface separating the two fluids. Every one knows the phenomenon which happens in this case, and which amuses children under the denomination of Ducks and Drakes ; but Μ. d’Alembert was the first who explained it in a satisfactory and philosophical manner.

Two years after his election to a place in the academy he published his treatise on Dynamics. The new principle developed in this treatise consisted in establishing equality, at each instant, between the changes that the motion of a body has undergone, and the forces or powers which have been employed to produce them; or, to express the thing otherwise, in separating into two parts the action of the moving powers, and considering the one as producing alone the motion of the body in the second instant, and the other as employed to destroy that which it had in the first.

So early as the year 1744, Μ. d’Alembert had applied this principle to the theory of the equilibrium, and the motion of fluids; and all the problems before solved by geometricians became in some measure its corollaries. The discovery of this new principle was followed by that of a new calculus, the first trials of which were published in a Discourse on the General Theory of the Winds, to which the prize-medal was adjudged by the academy of Berlin in the year 1746, and which was a new and brilliant addition to the fame of Μ. d’Alembert.

He availed himself of the favourable circumstance of the king of Prussia having just terminated a glorious campaign by an honourable peace, and in allusion to this, dedicated his work to that prince in the three following Latin verses :—
Hoec ego de ventis, dum ventorum ocyor alis
Palantes agit Αustriacos Frcdericus, et orbi,
Insignis lauro, ramum proetendit olivee.
Swifter than wind, while of the winds I write,
The foes of conquering Frederick speed their flight;
While laurel o’er the hero’s temple bends,
To the tir’d world the olive branch he sends.

This flattering dedication procured the philosopher a polite letter from Frederick, and a place among his literary friends.
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In the year 1747 D’Alembert applied his new calculus of Partial Differences to the problem of vibrating chords, the solution of which, as well as the theory of the oscillation of the air and the propagation of sound, had been given but incompletely by the geometricians who preceded him, and these were his masters or his rivals.

In the year 1749 he furnished a method of applying his principles to the motion of any body of a given figure; and he solved the problem of the precession of the equinoxes, determined its quantity, and explained the phenomenon of the nutation of the terrestrial axis, discovered by Dr Bradley.

In 1752 Μ. d’Alembert published a treatise on the Resistance of Fluids, to which he gave the modest title of an Essay, but which contains a multitude of original ideas and new observations. About the same time he published, in the Memoirs of the Academy of Berl in, Researches concerning the Integral Calculus, which is greatly indebted to him for the rapid progress it has made in the present century.

While the studies of Μ. d’Alembert were confined to geometry, he was little known or celebrated in his native country. His connections were limited to a small society of select friends: he had never seen any man in high office except Messrs d’Argenson. Satisfied with an income which furnished him with the necessaries of life, he did not aspire after opulence or honours, nor had they been hitherto bestowed upon him, as it is easier to confer them on those who solicit them, than to look out for men who deserve them. His cheerful conversation, his smart and lively sallies, a happy knack at telling a story, a singular mixture of malice of speech with goodness of heart, and of delicacy of wit with simplicity of manners, rendered him a pleasing and interesting companion; and his company, consequently, was much sought after in the fashionable circles. His reputation at length made its way to the throne, and rendered him the object of royal attention and beneficence. He received also a pension from government, which he owed to the friendship of Count d’Argenson.

The tranquillity of Μ. d’Alembert was abated when his fame grew more extensive, and when it was known beyond the circle of his friends, that a fine and enlightened taste for literature and philosophy accompanied his mathematical genius. Our author’s eulogist ascribes to envy, detraction, and to other motives equally ungenerous, all the disapprobation, opposition, and censure that Μ. d’Alembert met with on account of the publication of the famous Encyclopedical Dictionary of Arts and Sciences, in conjunction with Diderot. None surely will refuse the well-deserved tribute of applause to the eminent displays of genius, judgment, and true literary taste, with which Μ. d’Alembert has enriched the great work now mentioned. Among others, the Preliminary Discourse which he has affixed to it, concerning the rise, progress, connections, and affinities of all the branches of human knowledge, is perhaps one of the first productions of which the philosophy of the present age can boast, and will be regarded as a striking specimen of just arrangement and sound criticism, and also as a model of accurate thinking and elegant writing.

Some time after this D’Alembert published his Philosophical, Historical, and Philological Miscellanies. These were followed by the Memoirs of Christina, Queen of Sweden, in which Μ. d’Alembert showed that he was acquainted with the natural rights of mankind, and was bold enough to assert them. His Essay on the Intercourse of Men of Letters with Persons high in Rank and Office wounded the former to the quick, as it exposed to the eyes of the public the ignominy of those servile chains which they feared to shake off or were proud to wear. A lady of the court hearing one day the author accused of having exaggerated the despotism of the great, and the submission they require, answered slyly, If he had consulted me, I would have told him still more of the matter.

Μ. d’Alembert gave very elegant specimens of his literary abilities in his translations of some select pieces of Tacitus. But these occupations did not divert him from his mathematical studies; for about the same time he enriched the Encyclopédie with a multitude of excellent articles in that line, and composed his Researchesοη several important points of the System of the World, in which he carried to a higher degree of perfection the solution of the problem of the perturbations of the planets, that had several years before been presented to the Academy.

In 1759 he published his Elements of Philosophy; a work extolled as remarkable for its precision and perspicuity; in which, however, are some tenets, relative both to metaphysics and moral science, that are far from being admissible.

The resentment that was kindled, and the disputes that followed it, by the article Geneva, inserted in the Encyclopédie, are well known. Μ. d’Alembert did not leave this field of controversy with flying colours. Voltaire was an auxiliary in the contest; but as, in point of candour and decency, he had no reputation to lose, and as he weakened the blow of his enemies by throwing both them and the spectators into fits of laughter, the issue of the war gave him little uneasiness. It fell more heavily on D’Alembert, and exposed him, even at home, to much contradiction and opposition.

It was on this occasion that the late king of Prussia offered him an honourable asylum at his court, and the place of president of his academy; and was not offended at his refusal of these distinctions, but cultivated an intimate friendship with him during the rest of his life. He had refused, some time before this, a proposal made by the empress of Russia to intrust him with the education of the grand duke; a proposal accompanied with all the flattering offers that could tempt a man ambitious of titles or desirous of making an ample fortune; but the objects of his ambition were tranquillity and study.

In the year 1765 fie published his Dissertation on the Destruction of the Jesuits. This piece drew upon him a swarm of adversaries, who confirm the merit and credit of his work by their manner of attacking it.

Besides the works already mentioned, he published nine volumes of memoirs and treatises under the title of Opuscules, in which he has solved a multitude of problems relative to astronomy, mathematics, and natural philosophy; of which our panegyrist gives a particular account, more especially of those which exhibit new subjects, or new methods of investigation.

He published also Elements of Music, and rendered at length the system of Rameau intelligible; but he did not think the mathematical theory of the sonorous body sufficient to account for the rules of that art. He was always fond of music; which, on the one hand, is connected with the most subtile and learned researches of rational mechanics; while, on the other, its power over the senses and the soul exhibits to philosophers phenomena no less singular, and still more inexplicable.

In the year 1772 he was chosen secretary to the French academy. He formed, soon after this preferment, the design of writing the lives of all the deceased academicians from 1700 to 1772; and in the space of three years he executed this design, by composing 70 eulogies.

Μ. d’Alembert died on the 29th of October 1783. There were many amiable lines of candour, modesty, disinterestedness, [7:2:399]and beneficence, in his moral character; which are described, with a diffusive detail, in his éloge, by ,M. Condorcet, Hist, de l’Acad. Royale des Sciences, 1783.