Paris: Gauthier-Villars, 1869. Wraps. First Edition. 1635 pp. 4to. Wear and cuffing to original light salmon colored wraps. Original paper label pasted to spine with Volume # and year handwritten in black ink. Clean within, most pages uncut. Text in French. Very Good.
Important paper in which Jules Janssen describes his observation of the spectral line in the sun that was later determined to be a new element (helium), the only element initially discovered outside the earth. Norman Lockyer observed the same spectral line several months later and even later determined that it represented a new element. Lockyer and Janssen are both credited with the discovery.