Jules Janssen

Pierre Jules Cesar Janssen, usually known as Jules Janssen, was a French astronomer, born in Paris in 1824, who with Joseph Norman Lockyer is credited with discovering the gaseous nature of the solar chromosphere and, with some justification, the element helium. He studied mathematics and physics and spent much of his career on scientific missions, among them a trip to Peru in 1857 to find the magnetic equator, observations of the transits of Venus in 1874 in Japan and 1882 in Algeria, and many solar eclipse expeditions. In 1875 he became director of the new astrophysical observatory at Meudon, and in 1893 he built an observatory on the summit of Mont Blanc. He presided over the Societe Astronomique de France from 1895 to 1897.