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‎Ueber Diffusion. (Fick). (+ Helmholtz:) Ueber Zusammensetzung von Spectralfarben. (Theilweis vorgetragen in der Zusammenkunft der British Association zu Hull in September 1854).‎

‎Leipzig, Johann Ambrosius Barth, 1855. Without wrappes. In: ""Annalen der Physik und Chemie. Hrsg. von J.C. Poggendorff"", 94. Bd., No 1 (""Heft"" No 1, 1855). Pp. 1-176 a. 4 folded engraved plates. (Entire issue offered). Titlepage to vol. 94 (small stamp on verso). Fick's paper: pp. 59-86. Helmholtz's paper: pp. 1-28. Clean and fine.‎

‎First appearance of Fick's importent paper in molecular physics in which he annouced his two laws of diffusion.Fick's first law relates the diffusive flux to the concentration field, by postulating that the flux goes from regions of high oncentration to regions of low concentration, with a magnitude that is proportional to the concentration gradient (spatial derivative). - Fick's second law predicts how diffusion causes the concentration field to change with time. (Wikipedia).First appearance of HELMHOLTZ'S fundamental paper in physiological optics in which he examined the sensitivity of the eye for the individual elements of the violet end of the spectrum" he was able to detect a whole series of distinct tones of purple: he alters the name 'invisible rays' to that of 'ultra-violet rays'" discussion of the relations of the wavelenghts of complementary colours and the intensity required if the mixture of simple complementarity colours is to produce white. He answered these questions quantatively. ""THE TREATISE (the paper offered), WHICH HAS BEEN FUNDAMENTAL FOR ALL LATER WORK OF THE SAME KIND, concludes with an inquiry into the validity of Newton's Colour Circle, which Helmholtz designates as one of the most brilliant inspirations of that great thinker.""(Leo Koenigsberge ""Hermann von Helmholtz"" pp. 131-133).‎