Jean Picard

Also found in: Wikipedia.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Picard, Jean


Born July 21, 1620, in La Flèche, Anjou; died July 12, 1682, in Paris. French astronomer. Member of the Académie des Sciences in Paris (1666).

A student of the French materialist philosopher P. Gassendi, Picard became professor of astronomy at the Collège de France in 1655. In 1669 and 1670, on a commission from the academy, he measured the length of the arc of the meridian between Paris and Amiens to be 1° 22′ 55″. In this measurement, he used the method of triangulation and was the first to measure angles by means of optical tubes with reticles instead of diopters. According to his measurements, the length of a degree of a meridian is equal to 111.21 km-the length is 111.18 km according to modern data. The data Picard obtained on the earth’s dimensions were used by I. Newton for numerical confirmation of the law of universal gravitation.

Picard invented the method of determining the right ascensions of heavenly bodies by observing, with the aid of a pendulum clock, the times when the bodies cross the meridian. For this purpose, he proposed in 1669 the fixing of a quadrant in the meridian, but this was not done at the Paris Observatory until 1683. In 1671 he conducted an excavation of Tycho Brahe’s observatory Uraniborg in Denmark. In 1672, together with G. Cassini, he performed observations at Paris of the planet Mars with the aim of determining the solar parallax. Picard founded the astronomical journal La Connaissance des Temps in 1679; he was compiler and editor of the journal’s first four volumes.


Degré du méridien entre Paris et Amiens. Paris, 1740.
Mesure de la Terre. Paris, 1671.
Voyage d’Uranibourg.… Paris, 1680.


Delambre, J. B. J. Histoire de l’astronomie moderne, vol. 2. Paris, 1821.
Boquet, F. Histoire de l’astronomie. Paris, 1925.
Defossez, L. Les Savants du XVII siècle et la mesure du temps. Paris, 1946.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
In 1669-1670, the Frenchman Jean Picard was able accurately to measure the size of the earth by extrapolating from the distance of one degree of latitude measured in the French countryside.
Cassini was interested in the true size and shape of Earth, and he continued Jean Picard's geodetic effort to establish the accurate length of an arc of longitude from the English Channel through Paris Observatory to the Mediterranean.
Anniversaries: 1620: Birth of French astronomer Jean Picard; 1796: Death of Scottish poet Robert Burns; 1897: Tate Gallery opened in London; 1884: Lord's Cricket Ground staged its first Test match when England played Australia; 1899: Birth of American no velist Ernest Hemingway: 1969: American astronaut Commander Neil Armstrong became the first man to land on the moon.