Jean le Rond D’alembert, one of the most distinguished mathematicians of the last century, owed none of his eminence to the accidents of birth or fortune. Even to a name he had no legal title; he derived the one half of that which he bore from the church of St. Jean le Rond in Paris, near which he was exposed; and the other probably from his foster-mother, a glazier’s wife, to whose care he was intrusted by a commissary of police, who found him. It is conjectured that both the exposure and the adoption of the infant were preconcerted; for a short time the father appeared, and settled on him a yearly pension of twelve hundred francs, equivalent to about £50.

Owing to these circumstances the date of D’Alembert’s birth is not exactly known; it is said to have been the 16th or 17th of November, 1717. He commenced his studies at the CollÈge des Quatre Nations when twelve years old. Mathematics and poetry seem to have been his favourite pursuits, since his instructors, he says, endeavoured to turn him from them; making it a charge against the former, that they dried up the heart, and recommending that his study of the latter should be confined to the poem of St. Prosper upon Grace. He was permitted, however, to study the rudiments of mathematics: and we may infer that he was little indebted either to books or teachers, from the mortification which he felt somewhat later in life, at finding that he had been anticipated in many things which he had believed to be discoveries of his own. He meant, at one time, to follow the profession of the law, and proceeded so far as to be admitted an advocate. Finding this not to his taste, he tried medicine; and, resolute in good intentions, sent his mathematical books to a friend, to be retained till he had taken his doctor’s degree. But he reclaimed book after book on various pretexts, and finally determined to content himself with his annuity of fifty pounds, and liberty to devote his whole time to the scientific pursuits which he loved so much. His mode of life at this period has been described by himself:—“He awoke,” he says, “every morning, thinking with pleasure on the studies of the preceding evening, and on the prospect of continuing them during the day. When his thoughts were called off for a moment, they turned to the satisfaction he should have at the play in the evening, and between the acts of the piece he meditated on the pleasures of the next morning’s study.”

The history of D’Alembert’s life is soon told. Some memoirs written in 1739 and 1740, and some corrections which he made in the Analyse DÉmontrÉe of Reynau, a work then much esteemed in France, obtained for him an entrance into the AcadÉmie des Sciences in 1741, at the early age of twenty-four. Simple in his habits, careless of his own advancement, or of the favours of great men, he refused several advantageous offers, which would have withdrawn him from the society of Paris, and from the libraries and other literary advantages of that great metropolis. Frederic II. of Prussia sought to tempt him to Berlin in 1752, and again in 1759. The invitation was again repeated and urged upon him in 1759 and 1763; and on the last occasion the King assured D’Alembert that, in rejecting it, he had made the only false calculation of his whole life. In 1762 Catharine of Russia wished him to undertake the education of her son, and endeavoured to overcome his reluctance to leave Paris, by promising him an income of ten thousand francs, and a kind reception to as many of his friends as would accompany him. “I know,” she said, “that your refusal arises from your desire to cultivate your studies and your friendships in quiet. But this is of no consequence: bring all your friends with you, and I promise you that both you and they shall have every accommodation in my power.” But his income had been rendered sufficient for his wants by a pension of twelve hundred francs from the King of Prussia, and an equal sum from the French Government; and he declined to profit by any of these liberal offers.

It is to D’Alembert’s honour that, until the end of her life, he repaid the services of his foster-mother with filial attention and love. It is said that when his name became famous, his mother, Mademoiselle de Tencin, a lady of rank and wit, and known in the literary circles of the day, sent for him, and acquainted him with the relationship which existed between them. His well-merited reply was, “You are only my step-mother, the glazier’s wife is my mother.” He lived unmarried, but the latter years of his life were overcast in consequence of a singular and unfortunate attachment to a M^lle. de l’Espinasse, a young lady of talent, whose society was much courted by the literary men of Paris. She professed to return this attachment; insomuch that when D’Alembert was attacked by a severe illness in 1765, she insisted on becoming his nurse, and after his recovery took up her abode under his roof. The connexion is said to have been purely Platonic; and this, it has been observed, may be believed, because, had the fact been different, there was little reason for concealing it, according to the code of morals which then regulated Parisian society. But the lady proved fickle; and worse than fickle, for she treated D’Alembert, who still retained his affection for her, with contempt and unkindness. Yet this ill usage did not alienate his regard. Upon her death he fell into a state of profound melancholy, from which he never entirely recovered. He died October 29, 1783. Not having conformed, on his death-bed, to the requisitions of the Roman church, some difficulty was experienced in procuring the rites of burial; and in consequence his interment was strictly private.

In his personal character D’Alembert was simple, benevolent, warm in his attachments, a sworn foe to servility and adulation, and no follower of great men. This temper stood in the way of his progress to riches. It was his maxim, that a man should be very careful in his writings, careful enough in his actions, and moderately careful in his words; and the latter clause was probably that which he best observed. In more than one instance his plain drollery gave offence to persons of influence at court, and frustrated the exertions of his friends to improve his fortunes. Fortunately he united simple tastes with an independent, fearless, and benevolent mind; and it is said that he gave away one half of his income, when it did not amount to £350. His own account of his own character, written in the third person, runs in the following terms, and is confirmed by the testimony of his friends:—“Devoted to study and privacy till the age of twenty-five, he entered late into the world, and was never much pleased with it. He could never bend himself to learn its usages and language, and perhaps even indulged a sort of petty vanity in despising them. He is never rude, because he is neither brutal nor severe; but he is sometimes blunt, through inattention or ignorance. Compliments embarrass him, because he never can find a suitable answer immediately; when he says flattering things, it is always because he thinks them. The basis of his character is frankness and truth, often rather blunt, but never disgusting. He is impatient and angry, even to violence, when any thing goes wrong, but it all evaporates in words. He is soon satisfied and easily governed, provided he does not see what you aim at; for his love of independence amounts to fanaticism, so that he often denies himself things which would be agreeable to him, because he is afraid that they would put him under some restraint; which makes some of his friends call him, justly enough, the slave of his liberty.” In his religious opinions D’Alembert was, in the true meaning of the word, a sceptic, and his name has obtained an unenviable notoriety as co-editor, with Diderot, of the celebrated EncyclopÉdie. His superintendence, however, extended only to the end of the second volume, after which the work was stopped by the French Government; and on its resumption D’Alembert confined himself strictly to the mathematical department. In one respect his conduct may be advantageously contrasted with that of some of his colleagues; he intruded his own opinions on no man, and he took no pleasure in shocking others, by insulting what they hold sacred. “I knew D’Alembert,” says La Harpe, “well enough to say that he was sceptical in every thing but mathematics. He would no more have said positively that there was no religion, than that there was a God; he only thought that the probabilities were in favour of theism, and against revelation. On this subject he tolerated all opinions: and this disposition made him think the intolerant arrogance of the Atheists odious and unbearable. I do not think that he ever printed a sentence, which marks either hatred or contempt of religion.”

We proceed to mention the most remarkable of D’Alembert’s mathematical works. He published in 1743 a treatise on Dynamics, in which he enunciated the law now known under the name of D’Alembert’s principle, one of the most valuable of modern contributions to mechanical science. In the following year appeared a treatise on the Equilibrium and Motion of Fluids; and in 1746, Reflections on the general Causes of Winds, which obtained the prize of the Academy of Berlin. This work is remarkable as the first which contained the general equations of the motion of fluids, as well as the first announcement and use of the calculus of partial differences. We may add to the list of his discoveries, the analytical solutions of the problem of vibrating chords, and the motion of a column of air; of the precession of the equinoxes, and the nutation of the earth’s axis, the phenomenon itself having been recently observed by Bradley. In 1752 he completed his researches into fluids, by an Essay on the Resistance of Fluids. We have to add to the list his Essay on the Problem of Three Bodies, as it is called by astronomers, an investigation of the law by which three bodies mutually gravitating affect each other; and Researches on various points connected with the system of the Universe: the former published in 1747, and the latter in 1754–6. His Opuscules, or minor pieces, were collected in eight volumes, towards the end of his life.

Of his connexion with the EncyclopÉdie, we have already spoken. He is said to be singularly clear and happy in his expositions of the metaphysical difficulties of abstract science. He is also honourably known in less abstruse departments of literature by his MÉlanges de Philosophie, Memoirs of Christina of Sweden, Essay on the Servility of Men of Letters to the Great, Elements of Philosophy, and a work on the Destruction of the Jesuits. On his election to the office of perpetual Secretary to the Academy, he wrote the Eloges of the members deceased from 1700 up to that date. His works and correspondence were collected and published in eighteen volumes 8vo. Paris, 1805, by M. Bastien, to whose first volume we refer the reader for complete information on this subject.