J. B., J., an eminent mathematician and astronomer, was born at Amiens on the 19th September 1749. He studied in the gymnasium of that town, and by his intimate acquaintance with the Latin and Greek languages, as well as his amiable disposition and prodigious memory, he drew the attention of his preceptor, the celebrated French poet, the Abbé Delisle, who at that time taught in the college. This was the beginning of a friendship between them, which only terminated with the life of the poet.

Having accomplished his first course of studies, it remained to pursue in Paris a career begun under such favourable auspices; but the expense exceeded his resources. Fortunately, however, his family had formerly found a gratuitous place for a limited time in one of the great colleges of the University of Paris: the town of Amiens, which appears to have had the disposal of it, bestowed it on Delambre; and thus the benefit of an act of beneficence was reflected back on its source.

The time during which he was to enjoy the advantage he had obtained passed away, and his family, subjected to many other kinds of expense, left him to provide for himself. In this state he passed more than a year in expectation of a better situation, and supported with constancy very great privations. It was then that he gave himself up to those historical and literary studies which were the origin of his future labours. He undertook extensive translations of works in the Latin, Greek, Italian, and English languages, not for the sake of gain, which, however, he might have Delambre, got, but solely with a view to complete his studies. From the same motive he entered on the study of the mathematical sciences.

The great merit of Delambre, the habitual suavity of his character and manners, and the resolution he had taken to begin anew the entire course of his studies, and proceed, by his own efforts alone, engaged the attention of some, who advised him to consecrate a few years to the giving of instruction; and with this view he went to Compiègne; but he soon returned to Paris, a residence in which was now essentially necessary to his studies. There he pursued the same career, but with increased advantages; and this procured him a competent and independent subsistence.

He now yielded to the natural impulse of his mind in the pursuit of knowledge, studying profoundly the different mathematical theories, as also physics and astronomy; and continuing to cultivate history and general literature. No one could proceed with more system, or show more constancy in exploring the vast field of human knowledge; indeed perseverance was a distinguishing feature of his character. When he presented himself at the College of France to follow the lessons of Lalande, he had already read the works of that astronomer, and had made a complete commentary on them. This was first remarked when, in the course of instruction, an occasion offered to him of citing from memory a passage of Aratus. Lalande immediately foresaw the advantages his pupil was likely to confer on science, and from that moment regarded Delambre as a fellow-labourer. He entrusted to him the most complicated astronomical calculations, and prevailed on M. Dassy, whose son had received lessons from Delambre, to establish an observatory at his house, where Delambre applied himself to astronomical observations. He at the same time undertook the most extensive researches; he formed the design of completing the astronomical tables; and he dedicated his life to the study and the description of the heavens, a resolution he had previously entertained during his stay at Compiègne.

In the year 1781 the discovery of the Georgium Sidus or Uranus, by Herschel, excited general attention among astronomers; and the Academy of Sciences proposed the determination of its orbit as the subject of one of its annual prizes. Delambre undertook the formation of tables of its motion, and the prize was awarded to him for his labour. His next effort was the construction of solar tables, also tables of the motions of Jupiter and Saturn; he likewise undertook the construction of elliptical tables of the satellites of Jupiter, and in a few years he completed that laborious and extensive work. He took part in the sitting of the Academy of Sciences when Laplace communicated his important discoveries on the inequalities of Jupiter and Saturn; and he formed the design of applying the result of that profound analysis to the completion of tables of the two planets. Delambre applied himself more especially to the satellites of Jupiter, an undertaking of great difficulty and extent. In this he was sustained by two powerful motives, public utility, and the dignity of the subject. He had been engaged for several years in the composition of his elliptical tables, when the Academy of Sciences proposed the same question as the subject of a prize: it was awarded to his labours, and soon afterwards, viz. in 1792, he was elected a member of the academy.

The great diversity of weights and measures, and the consequent inconvenience to commerce, engaged the attention of the French nation about the time of the first revolution; and in the year 1790, Talleyrand, then minister of foreign relations, brought the subject before the constituent assembly, where it was resolved that the king should be requested to apply to his Britannic majesty, with the view of getting the English parliament to concur with the national assembly in fixing on some natural unit as a standard. It was proposed that commissioners from the Academy of Sciences should meet an equal number of members of the Royal Society of London, in order to ascertain the length of a pendulum in some determinate latitude, and thence to deduce an invariable model for all weights and measures; and a commission, composed of Borda, Lagrange, Laplace, Monge, and Condorcet, was appointed to consider this grand project. Besides the length of the pendulum, two other units were suggested, namely, a quadrant of the elliptic meridian, and a fourth part of the earth's circumference at the equator. Of the three, the commission adopted the quadrant of the meridian, and its execution was begun by appointing Delambre and Méchain to measure an arc from Dunkirk to Barcelona. This undertaking, in itself laborious, was, by circumstances which arose out of the revolution, rendered highly dangerous to the personal safety of those engaged in it. Méchain died whilst the work was proceeding, and its successful termination was at last accomplished by the zeal, the talents, the perseverance, and the prudence of Delambre. The details of this grand labour have been consigned to posterity in his work entitled Base du Système Métrique Décimal, the first volume of which bears the date of 1806, and the third and last that of 1810. The labours of Delambre and Méchain were followed up by those of Biot and Arago, who have added as a supplement to the Base du Système Métrique their Recueil d'Observations Géodésiques, Astronomiques, et Physiques, published in 1820, in which the operations are detailed by which the measurement of the meridian was prolonged from Barcelona to Formentera in the Mediterranean. Altogether this work does honour to the nation which produced such mathematicians, astronomers, and artists as were united in the execution of the labours detailed in it, but particularly to Delambre, the great directing mind that in the course of eight years brought them to a successful termination. The opinion of the National Institute of France was solemnly expressed when, having considered what had been the most important application of the mathematical and physical sciences during the preceding ten years, the universal suffrages of the members decreed the prize to the author of the Base du Système Métrique.

Delambre, who had been chosen as an associate of almost every scientific body in Europe, and a member of the French Board of Longitude, was appointed perpetual secretary for the mathematical sciences in the Institute. He had succeeded Lalande in the chair of astronomy of the College of France, and he was appointed one of the principal directors (titulaires) of the university. For twenty years he executed the duties of his office in one of the classes of the Institute, and, in doing so, he enjoyed the reputation of being impartial, faithful, and just. His annual reports, his historical cloges, which have been published, and his exposition of the progress of science, are eminently distinguished by profound erudition, a talent for writing formed on the best models, and, above all, by a disposition of mind which inclined him to place in the most favourable light the works of others, as far as was consistent with historical truth. His literary and scientific labours were very numerous, and, in respect to excellence, of the highest order. His History of Astronomy, comprehended in six quarto volumes (a seventh has been promised), is a work of prodigious research. It puts the modern astronomer in possession of all that has been done, and of the methods employed by those who have gone before him.

His Méthodes Analytique pour la Détermination d'un Arc du Méridien, his numerous memoirs in the additions to the Connaissances des Temps, and his Astronomie Théorique et Delambre, Pratique, exhibit the finest applications of the modern analysis to astronomy and geography; in fact, they have given a new turn to these sciences. Astronomers have now laid aside the purely geometrical methods, which, however elegant, always required at last numerical calculations, and instead of these, have expressed every thing to be determined in astronomy by compact analytical formulæ, of which a great number are due to Delambre.

It is a remarkable fact in the life of Delambre, that he did not apply himself to astronomical observations until he was about thirty-five years of age; whereas in general, the particular subject in which a man is destined to excel attracts his attention in early youth. In one respect this was verified in the case of Delambre, for he manifested an early promptitude in the acquisition of languages; but instead of spending his life in the study of mere words, he made his skill in languages the key to knowledge, and rendered it subservient to the elucidation of the history of an important science, astronomy.

Delambre was appointed a member of the Royal Council of Public Instruction in the year 1814; a place, however, which he lost in 1815. He was in Paris when it was taken by the allied armies; and in a letter written at that time to a friend and pupil, he says, that on the day of the siege, in the hearing of the cannonade, he laboured with tranquillity in his study from eight in the morning till midnight. He had a happier fate than the unfortunate Sicilian geometer Archimedes in a like position, for not only was he not molested by the victors, but no military man was even billeted on him, probably from respect to his high reputation. At the creation of the legion of honour, Delambre was made a member of that order. He was appointed chevalier of St Michael in 1817, an officer in the legion of honour in 1821, but a long time before he was created a hereditary chevalier, with an endowment, which was decreed as a national reward.

The life of continued and hard study which Delambre led at last affected his health. The disease by which he was cut off became apparent in the month of July 1822. His total loss of strength, with frequent and long-continued fainting fits, gave warning of a fatal result. He foresaw what was about to happen, but he preserved to the last moment the unalterable mildness of his character, and the serenity of his mind. At last, on the 19th of August 1822, at the age of seventy-two, he sunk under his disease, not without having suffered, but without having complained, or betrayed any symptoms of impatience.

The following is a list of his works which appeared separately: 1. Tables de Jupiter et de Saturn, 1789; 2. Tables du Soleil, de Jupiter, de Saturn, d'Uranus, et des Satellites de Jupiter, pour servir à la 3me édition l'Astronomie de Lalande, 1792; 3. Méthodes Analytiques pour la Détermination d'un Arc du Méridien, 1799; 4. Tables Trigonométriques Décimales, par Borda, revues, augmentées, et publiées par M. Delambre, 1801; 5. Tables du Soleil (publiées par le Bureau des Longitudes), 1806; 6. Base du Système Métrique Décimal, &c. 3 vols. in 4to, 1806-1810; 7. Rapport Historique sur les Progrès des Sciences Mathématiques depuis 1789, &c. 1810; 8. Abrégé d'Astronomie, ou Leçons Élémentaires d'Astronomie Théorique et Pratique, in 8vo; 9. Astronomie Théorique et Pratique, 3 vols. in 4to, 1814; 10. Tables Écliptiques des Satellites de Jupiter, 1817; 11. Histoire de l'Astronomie Ancienne, 2 vols. in 4to; 12. Histoire de l'Astronomie du Moyen Age, 1819, 1 vol. in 4to; 13. Histoire de l'Astronomie Moderne, 1821, 2 vols. in 4to; 14. Histoire de l'Astronomie au Dix-huitième Siècle, 2 vols. in 4to, 1827 (only one yet published, 1833).

In addition to these, he furnished a very considerable number of memoirs (about twenty-eight) on various points of astronomy, to the Connaissances de Temps, beginning with the year 1788. He also contributed to the Memoirs of the Academies of Stockholm, Petersburg, Berlin, and Turin, and to those of the first class of the French Institute; and he composed elegies on many of his predeceased contemporaries, among which may be noticed one on our highly distinguished countryman Dr Maskelyne, the astronomer-royal of England.

In conclusion, we may remark, that Delambre has rendered essential service to true knowledge by the pains he took to dispel a delusion which had been propagated by his friend Bailly regarding the antiquity of the Indian astronomy. Almost every one is now satisfied that the Indian tables, so far from having been composed from observations made at so remote a period as 3000 years ago, are probably not older than about 700 years. This was the decided opinion of Delambre, and in this he has been supported by the authority of Laplace.