Presentation / Talk

Heinrich Wild's Polaristrobometer: An early form of chemical polarimeter

The year 2011 having been proclaimed by UNESCO and IUPAP “International Year of Chemistry”, it seems fitting to have a close look at a physical chemistry instrument, the Polaristrobometer, an early form of polarimeter/saccharimeter, at its inventor, the Swiss physicist Heinrich Wild, at its enthusiastic reception by chemists, and at its principal manufacturer, Hermann & Pfister at Bern. Heinrich Wild (1833-1902) was appointed professor of physics at the University of Bern and director of the (mainly meteorological) Observatory in 1858. Called in 1868 to the direction of the Central Physical (Meteorological) Observatory in Saint Petersburg, he spent the next 27 years in Russia, extending enormously the network of observing stations and working on the improvement and standardisation of meteorological instruments. He retired to Zurich in 1895. His Polaristrobometer, first described in 1865, is built around the very sensitive polariscope invented by Savart a quarter of a century earlier. To achieve the measurement of the angle of rotation of the plane of polarisation of monochromatic light by optically active substances, the polariser is rotated until a network of parallel interference fringes disappears, as opposed to the more modern types of polarimeters where one looks for an equality of tint or of luminosity of two or more adjacent fields. This truly original, precise and practical polarimeter remained the best one available until the end of the 19th century, when it was superseded by instruments less prone to systematic errors and more convenient to use.That the Polaristrobometer was much in demand by chemists and commercially successful is shown by the many citations and images in physics textbooks and, above all, by the long descriptions and detailed instructions appearing in books and articles written by chemists from 1875 onwards, notably by the pioneer of polarimetry H. Landolt. Today, many Polaristrobometers can be found, often unidentified, in remote corners of science museums. Hermann & Pfister (later Pfister & Streit) at Bern became the main, but not exclusive manufacturer of this instrument. A model of reduced size (tubes of 50 mm instead of 220 mm) was first made by J. G. Hofmann at Paris and by Dr. Meyerstein at Göttingen. Both models are still mentioned in the 1896 catalog of Schmidt & Haensch at Berlin.

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