‎"BECQUEREL, EDMOND (ALEXANDRE-EDMUND). - BECQUEREL'S ""CONTINUING RAYS"" OR THE ""BECQUEREL PHENOMENA""‎
‎Mémoire sur le rayonnement chimique qui accompagne la lumiere solaire et la lumiere électrique. (3e Mémoire.- Extrait par l'auteur).‎

‎(Paris, Bachelier), 1840. 4to. No wrappers. In: ""Comptes Rendus Hebdomadaires des Séances de L'Academie des Sciences"", Tome XI (No.18). Pp. (667-) 716. (Entire issue offered). Becquerel's paper:pp. 702-703. Some marginal brownspots, margins slightly soiled, light browning an creasing.‎

Reference : 47213

‎First printing of an importent paper in the history of photochemistry as he here discovered some effects of coloured rays of the solar spectrum.""Edmund Becquerel seems to be the first person to observe, in 1840 (in the paper offered), that the latent daguerreotype image which had been underexposed could be intensified if re-exposed to the yellow and red rays of the spectrum and then developed with mercury... Explaining this phenomenon, Becquerel called the yellow-red continuing rays (""rayon continuateurs"") in contrast to the primary rays, which exicited or produced the light image and which he called exiciting rays (""rayons excitateurs"").... They are dependent on the wave lenght of the light.""(Eder ""History of Photography"", pp. 265 ff.)""Becquerel was an early experimenter in photography. In 1840 he discovered that the silver halides, natively insensitive to red and yellow light, became sensitive to that part of the spectrum in proportion to their exposure to blue, violet and ultraviolet light, allowing Daguerreotypes and other photographic materials to be developed by bathing in strong red or yellow light rather than by chemical treatment. In practice this technique was rarely used."" (Wikipedia).‎