Sur la mesure optique des temperatures elevees in Comptes Rendus Hebdomadaires des Seances de L'Academie des Sciences, 114, 1892, pp. 214-216 [Full volume LE CHATELIER DESCRIBES HIS INVENTION OF THE OPTICAL PYROMETER]

FIRST EDITION OF THE 1892 PAPER IN WHICH LE CHATELIER DESCRIBES HIS INVENTION OF THE OPTICAL PYROMETER, an instrument that "provided the first reliable measurements of a number of temperatures of particular importance to science and industry" (DeWitt, Theory and Practice of Radiation Thermometry, 366). His invention measured temperature by comparing the light emitted from hot objects against a known standard; it was the first capable of measuring degrees of temperature over 3000 Celsius.

Henri Louis Le Chatelier "based this instrument, a modified Cornu photometer, on a suggestion by Becquerel in 1863 that high temperatures be measured optically in terms of the brightness of thermal radiation. In this instrument, the spectral luminance of a target image is compared to that of the central portion of the flame of an oil lamp, both viewed through a red filter, and the luminance of the target image is adjusted by means of an iris diaphragm on the objective lens until the two images have equal spectral luminances. The iris diaphragm is calibrated in terms of target temperature. The instrument was initially calibrated in terms of thermocouples calibrated in turn in terms of fixed-points determined by gas thermometry. Shortly after Wien's law was published, the Le Chatelier pyrometer was calibrated in terms of blackbody radiation" (ibid). CONDITION & DETAILS: Complete full volume. Paris: Gauthier-Villars, 1892, in Comptes Rendus Hebdomadaires des Seances de L'Academie des Sciences, 114. Pp. 1629. Entire volume. Ex-libris bearing only a deaccessioned stamp on the back of the title page and slight ghosting at the spine where a spine label has been removed. Bound in clean full blue cloth, gilt-lettered at the spine. Solidly and tightly bound. Clean and bright throughout.