Background

Jean Baptiste Joseph Delambre was born on September 19, 1749, in Amiens, France. He was the eldest of his parent's children. His father was a draper. Childhood illnesses at this time were extremely serious and when he developed smallpox at the age of 15 months his parents must have doubted that he would ever have much of a future.

Education

Delambre attended the Jesuit College in Amiens, studying under the abbé Jacques Delille who was a poet and classicist. There Delambre studied English and German but in 1764 the Jesuits were banned from France and at this stage he continued his education in Amiens, studying under teachers who had been brought from Paris. At this time he was intent on becoming a parish priest, but one of these new teachers encouraged him to continue his education in Paris.

Jean eventually won a small scholarship that enabled him to move on to Paris and the Collège du Plessis, where he studied literature (chiefly Latin and Greek) and history. He was especially skilled in languages and began to make translations of works in Latin, Greek, Italian, and English. Delambre was apparently so poor that upon graduation he lived for almost a whole year on a diet of bread and water.

Jean then was engaged as a private tutor in Compiègne and undertook private studies in mathematics, presumably so as to be able to teach this subject along with languages, literature, rhetoric, and history - in which he had received schooling. A local doctor seems to have suggested to Delambre that he might eventually learn astronomy. The opportunity to do so did not occur, however, until 1780, when Delambre had been established in Paris for some nine years. He was thus in his early thirties when he first began to study astronomy, the subject in which he was to establish his reputation.

Career

A most fortunate event that helped Delambre in his career occurred in 1771, when he became tutor to the son of Geoffroy d’Assy (receveur générale des finances) in Paris. Eventually d’Assy built a small, private, and apparently well-equipped observatory for Delambre’s use - acting on the suggestion made by the astronomer Lalande. Delambre had begun to attend Lalande’s lectures at the Collège de France in 1780, and he at once attracted the attention of Lalande when the latter made reference to the Greek poet Aratus, of the third century B.C., author of the astronomical poem Phaenomena. Delambre, who was endowed with a prodigious memory, thereupon recited the whole passage in question and went on to discuss various explanations and commentaries that had been made by different scholars. Lalande soon learned that Delambre had written a series of annotations and emendations to his own writings, notably his Astronomie, the course textbook. After reading Delambre’s notes, Lalande made him an assistant, and eventually Delambre became Lalande’s scientific collaborator. Lalande fondly referred to Delambre as his "meilleur oeuvre."

The beginning of Delambre’s career as an observer is dated (by himself) on a day in 1786 when only he and Messier, of all the astronomers in Paris, had seen the transit of Mercury across the sun. The event occurred three-quarters of an hour later than the time predicted by Lalande; the other observers, too easily discouraged, had given up. Delambre had more faith in Halley’s tables, whieh predicted the oceurrence of the transit an hour and a half later, and so he persevered. This particular episode is cited by Jacquinet as an example of the lack of precision in astronomical tables of that time. Delambre’s experience with the transit must have provided a strong incentive for making more accurate tables of various major astronomical phenomena.

Before long there was a public challenge to all astronomers to solve the problems of precise planetary motion. The Académie des Sciences announced a general competition for the prize of 1790 on the subject of the motion of the planet Uranus, which had been discovered by William Herschel in 1781. Some idea of the difficulty of the problem may be gained from the simple fact that these eight years of observation of Uranus represent only about one-tenth of its sidereal period. To determine the orbit and motion of Uranus, Delambre had to consider the perturbations produced by Jupiter and by Saturn: in short, he had to combine a skill in computation with a theoretical understanding of applied celestial mechanics. After winning the prize, he went on to establish himself as a foremost expert in positional astronomy. Eventually there followed tables of the sun, of Jupiter, of Saturn, and of the satellites of Jupiter. The above-mentioned tables were published by Lalande in a later edition of his Astronomie and earned two further honors for Delambre.

In 1788 the Academy decided to establish a “uniform system of measures” founded on some “natural and invariable base.” The plan for the new system of measures was formally approved by a decree of the Assembly of 8 May 1790, proposed by Talleyrand; it was approved by Louis XVI on the following 22 August. Delambre’s task was not merely to make a series of correlated astronomical observations and terrestrial measurements; he had also to carry out extremely laborious calculations. The latter were made especially tedious by the need to convert the observations from the new centesimal units of angle-measure (used in Delambre’s instruments) to the older units of degrees, on which all tables of logarithms and of trigonometric functions were then based.

The proponents of the metric system succeeded in establishing a decimal-positional system of mass and length (area and volume), but failed in their attempts to introduce similar systems of time or of angle measure. Delambre’s instruments were constructed with the new centesimal divisions, in anticipation of their general adoption.

In 1795 he was admitted to the Bureau des Longitudes, becoming President in 1800. In 1801 he was appointed secretary to the Académie des Sciences making him the most powerful figure in science in France. In 1803 his health took a turn for the worse when he developed rheumatic fever but he continued to devote most of his time to work. Delambre was appointed to the chair of astronomy at the Collège de France in Paris in 1807. The position had been held by Lalande until his death in that year and Delambre was proud to succeed his former teacher. He was also appointed treasurer to the Imperial University in 1808 and at this time moved with his wife from the d'Assy house in the le Marais district to the official residence of the Treasurer of the University.

He retired from public life in 1815.

Achievements

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  Jean Baptiste Joseph Delambre was one of the first astronomers to derive astronomical equations from analytical formulas. As scientist, Delambre is remembered primarily for his improvements in astronomical tables and his contributions to the measurement of the earth, and for establishment of the base of the metric system.
  
  In 1792 he was given the annual prize of the Academy, and he was elected as a membre associé in the section of sciences mathématiques. This election was a major factor in his being designated to make the fundamental geodetic measurements on which the metric system was to be based.
  
  Delamber was awarded in 1810 the decennial prize of the Institute for his publication of the base of the metric system. His name was also one of the 72 names inscribed on the Eiffel tower. In 1815 he was made a chevalier of Saint Michel. He was invested as chevalier of the Legion of Honour by Napoleon at the first such occasion in 1804 at the Hotel des Invalides in Paris, and in 1821 he was made an officier of the Legion of Honour.
  
  He is honoured by having a large lunar crater named after him.

Works

More photos

• book

  • Histoire De L'astronomie Ancienne 2012
  • Rapport Historique Sur Les Progrès Des Sciences Mathématiques Depuis 1789 2012
  • Tables Astronomiques 2012
  • Astronomie Théorique Et Pratique, Volume 3 2012
  • Base Du Système Métrique Décimal 2012
  • Grandeur Et Figure de la Terre 2018
  • Astronomie Théorique Et Pratique, Volume 2 2012

Membership

Delambre was a member of the Royal Swedish Academy of Sciences and a member of the American Academy of Arts and Sciences.

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  The Royal Swedish Academy of Sciences , Stockholm

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  The American Academy of Arts and Sciences , Cambridge

Personality

Delambre was afraid losing his ability to read, so he devoured any book available and trained his memory.

Physical Characteristics: After a childhood fever, Delambre suffered from very sensitive eyes, and believed that he would soon go blind.

Given his poor eyesight it is even more remarkable that he took up astronomy, but it has to be said that his eyesight continued to improve during the thirty years following the smallpox. To give an indication of just how bad his eyesight still was when he was 20 years old, it should be noted that even at that time he could hardly read his own handwriting and could not bear to be in direct sunlight.

Connections

in 1804, Jean married Elizabeth-Aglaée Leblanc de Pommard, the widowed mother of his assistant. They lived at first in the d'Assy house in the le Marais district of Paris where, except for when he had been on his travels, he had continued to observe in the observatory above his room from the time it was first built for him.

Tragedy struck his family in 1807 when his wife's son, who had previously been Delambre's assistant, died in Naples at the age of 26.

Spouse:

Elisabeth-Aglaée Leblanc de Pommard

References

• The Measure of All Things
  2003