JANSSEN, PIERRE JULES CÉSAR - THE DISCOVERY OF HELIUM IN THE SUN.

Éclipse de Soleil du 18 Aout 1868. Rapport adressé par M. Janssen au Maréchal de France Président du Bureau des Longitude.

Paris, G. Masson, 1878. 8vo. Contemp. hcalf, raised bands, gilt spine. Light wear along edges. Small stamps on verso of titlepage. In: "Annales de Chimie et de Physique", 4e Series - Tome 15. 512 pp. a. 3 folded engraved plates. (The entire volume offered). Janssen's memoir: pp. 414-426.

First appearance of this milestone paper in chemistry, physics and astronomy, announcing the discovery of the helium lines in the spectrum of the sun. It was Lockyer in the same year that named it 'helium' for Helios, the Greek God of the Sun. Helium was not discovered on the earth before 1895 by William Ramsay, and it was Crookes who established its identity with the helium Janssen and Lockyer observed in the spectrum of the sun.

"He Janssen) met immortality by travelling to India in 1868 to study the total eclipse. It was then that he observed the helium line and forwarded the spectral data to ockyer. He also noted the size of the solar prominences. The day after the eclipse he attempted to take their spectra again and succeeded despite the absence of the obscuring moon. he then announced jubilantly that it was the day after the eclipse that was the real eclipse day for him. Lockyer also reported this method of studying prominences without an eclipse....Like Lockyer he lived to see his observation of the helium line vindicated by Ramsay's discovery of that element on earth."(Asimov).

"This (the discovery of helium lines in the sun by Lockyer) was announced on the same day by the French astronomer Janssen, who was in India observing a total eclipse. As a result, the French government some ten years later struck a medallion showing the heads of both scientists.
By that time, the two men had made a much more dramatic discovery at the same time, this time in cooperation. Janssen, studying the spectrum ofthe sun during the eclipse, had noted a fine line he did not recognize. he send a report on this to Lockyer, an acknowledges expert on solar spectra. Lockyer compared the reported position of the line with lines of known elements, concluding that it must belong to a yeat unknown element, possibly not even existing on the earth. He named the element, from the Greek word for the sun."(Asimov).

Parkinson "Breakthroughs" 1868 A. - The volume contains other notable papers by Dumas, Berthelot et al.

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