Abstract
AN article on “Le tricentenaire de 1'abbé Picard,” by M. E. Doublet, in the Revue générate des Sciences (September 15–30), directs attention to the tercentenary of the well-known French astronomer, Jean Picard, who was born on July 21, 1620. Very little is known about Picard's life, so that even the year of his death is uncertain (about 1683). He was a pupil of Gassendi, and took up the study of astronomy at latest in 1645, when he observed the eclipse of the sun on August 21 of that year, and it was as an observer that he was chiefly distinguished. Though he was not the first to apply telescopic sights to astronomical instruments, he was almost certainly not aware that this had many years before been done by William Gascoigne; but Picard was at any rate the first to make use of this invention in an extensive series of observations, when he, in 1669 and 1670, determined the size of the earth. This was done by a triangulation from Sourdon, near Amiens, to Malvoisine, south of Paris, on the plan first proposed and carried out by Snellius about fifty years earlier. Picard measured a base along a level and wellbuilt road from Villejuive to Juvissy, 5663 toises long. It is deserving of special notice that he compared his standard toise with the length of the seconds pendulum, “lest the same should happen to it as had happened to all previous standards ”; and that did indeed happen, for his toise is lost. The results of this, the first modern geodetic operation, were published in Picard's “Mesure de la terre” in 1671.
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DREYER, J. The Tercentenary of Jean Picard. Nature 106, 350–351 (1920). https://doi.org/10.1038/106350a0
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DOI: https://doi.org/10.1038/106350a0