Observations spectrales prises pendent l'éclipse du 18 août 1868, et methode d'observation des protubérances des éclipses... Calcutta, 3 octobre 1868.

(Paris, Gauthier-Villars), 1869. 4to. In: ""Comptes Rendus Hebdomadaires des Séances de L'Academie des Sciences"", Tome 68, No 7. Pp. (349-) 408. (Entire issue offered). Janssen's paper pp. 367-376.

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First printing of the paper in which Janssen announced the discovery of a new element. On August 18, 1868, Janssen managed to do just that. He became the first person to observe helium, an element never before seen on Earth, in the solar spectrum. At the time, though, Janssen didn’t know what he’d seen""just that it was something new""""Helium, the second most abundant element in the universe, was discovered on the sun before it was found on the earth. Pierre-Jules-César Janssen, a French astronomer, noticed a yellow line in the sun's spectrum while studying a total solar eclipse in 1868. Sir Norman Lockyer, an English astronomer, realized that this line, with a wavelength of 587.49 nanometers, could not be produced by any element known at the time. It was hypothesized that a new element on the sun was responsible for this mysterious yellow emission. This unknown element was named helium by Lockyer.""