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Published online by Cambridge University Press: 14 March 2018
In the account of an investigation of the optical properties of gypsum published by one of us (A. E. H. T.) in 1908 it was stated, as the result of direct measurement in sodium-light of the optic axial angle of a section-plate perpendicular to the first median line, which was heated in an air-bath, that the substance became uniaxial at 105.2° C. Three other section-plates examined subsequently gave somewhat higher values, the results ranging from 109.5° to 114.2° C. These figures were arrived at after a considerable correction, amounting to as much as 7°, had been applied for conduction along the crystal-holder, the temperatures actually observed being greater by this amount.
Page 257 note 1 Tutton, A. E. H., ‘The optical constants of gypsum at different temperatures, and the Mitscherlich experiment.’ Proc. Roy. Soc. London, 1908, ser. A, vol. lxxxi, pp. 40–57 CrossRefGoogle Scholar ; also with additions in Zeits. Kryst. Min., 1909, vol. xlvi, p. 135.
Page 258 note 1 Brauns, R., ‘Die Aenderung des optischen Achsenwinkels in Gips bei höherer Temperatur.’ Centralblatt Min., 1911, pp. 401–405 Google Scholar.
Page 259 note 1 Mineralogical Magazine, vol. xvi, p. xxx ; vide Nature, 1911, vol. lxzxviii, p. 105, where owing to a misprint the temperature is given as 25°.
Page 260 note 1 If only the bulb and a small portion of the stem were immersed this correction would probably lie between 0.5 and 1.0° C.
Page 263 note 1 This work has since been published in detail : E. H. Kraus and L. J. Youngs, ‘Üver die Änderungen dee optischen Achsenwinkels in Gips mit der Temporatur.’ Neues Jahrbuch Min., 1912, vol. i, pp. 128-146. It does not appear from the description what correction, if any, was applied for the exposed portions of the stems of the long thermometers employed ; and in reply to an inquiry, Professor Kraus has very courteously informed us that, as a matter of fact, no such correction was applied. He believes, however, that under the conditions of the experiments this correction could not in any case have exceeded 0.7° C.
