Voigt & Hochgesang Göttingen, c. 1875-80.
This is a petrographic microscope by Voigt & Hochgesang of Göttingen, a specialist company of petrographic mounts of rocks and minerals in thin sections and petrographic microscopes. In 1857, Rudolf Winkel (1827-1905), a German developer and manufacturer of microscopes, set up his business in Göttingen in order to produce precision instruments for the University of Göttingen. His first apprentice since 1858 was FG Voigt, who since 1869 established himself as the firm of Voigt & Hochgesang. The company specialized in the production of crystallographic-optical instruments and microscopical thin sections of rocks, minerals, fossils, etc.
The microscope, signed to the of the foot ‘VOIGT & HOCHGESANG, GÖTTINGEN’, is standing on a ‘Y’ shaped base with squat turned pillar supporting the microscope with a compass type joint to the underside of the stage, with a plano-concave mirror in a gimbal on an articulated arm, The rotating stage with a polarizer on a slide in/out dovetail with rack and pinion focusing, polarizer with engraved scale, stage with slide positioning scale and scale engraved around the edge, triangular support at the back incorporating screw operated fine focus with a large nickel plated adjustment wheel, with push/pull focusing, nosepiece with X-Y centering, with Klein's plate (a 3.75 mm thick quartz plate, cut perpendicular to the c-axis) in pull out slot, with eyepiece with cross-hairs and micrometer. The effect of the microscopes made by Hartnack is clearly evident, moreover: this microscope can use objectives having the Hartnack thread.
This extremely rare microscope is found today in only a few copies. It belongs to the first generation of truly petrographic microscopes that occurred from about 1870 in Germany. As opposed to previous microscopes, which were equipped with Nicol prisms to provide views of anisotropic crystalline materials between crossed polarizers, this new generation of dedicated petrographic microscopes were designed specifically for petrography. In that, the variability within the surviving copies suggests that these microscopes were made in very small numbers and according to the specifications of the buyers, making each instrument a one-off. A somewhat later version of this model (but with rack and pinion coarse focusing) is inventory number MW 94/545 in the Museum for the History of Sciences collection of Universiteit Gent, Belgium.
Such microscopes were produced by the Prussian maker Heinrich Ludwig Rudolf Fuess (1838-1917) of Berlin Kreuzberg since 1870 after the design by the pioneer petrographer Karl Heinrich Ferdinand Rosenbusch (1836-1914). In the Neues Jahrbuch für Mineralogie of 1876, Rosenbusch presented "A new microscope for mineralogical and petrographic investigations" declaring that it must be able to centrically rotate the examined object in its own horizontal plane with fixed crossed Nicols, read the angle by which it has been rotated and preserve the polarizing planes of the Nicols at known position.
Alphonse François Renard
A similar petrological microscope, now in the Science Museum in London (Inv. 1921-680/1), was used by the Belgian geologist and petrographer Alphonse François Renard (1842 – 1903) whilst working on deep-sea deposits in the Challenger expedition of 1872-76. With this microscope, Renard examined the various rock specimens and oceanic deposits submitted to him for examination in association with Sir John Murray, and their detailed observations were embodied in the Report on the Scientific Results of the Voyage of H.M.S. Challenger Deep Sea Deposits (1891). The more striking additions to our knowledge included the detection and description of cosmic dust, which as fine rain slowly accumulates on the ocean floor; the development of zeolitic crystals on the sea-bottom at temperatures of 32°F (0°C) and under; and the distribution and mode of occurrence of manganese nodules and of phosphatic and glauconite deposits on the bed of the ocean.
Karl Heinrich Ferdinand Rosenbusch
Comment by Daniel E. Kile, author of The Petrographic Microscope (the Mineralogical Record, 2003): This could be an early instrument, but it could also be a somewhat later microscope, the simple design being offered as a less-expensive alternative to a more elaborate petrographic instrument (such as is illustrated in my Mineralogical Record monograph (2003) on p. 25, Fig. 21). In any event, it is definitely not a first-generation Rosenbusch-style microscope! An unquestionably Rosenbusch-type instrument manufactured by V&H is indeed known; it is quite different than yours; for example, this early Rosenbusch microscope has a circular cross section for the arm, in contrast to the triangular cross section in later instruments. The Rosenbusch-pattern microscope carries a very low serial number of 65 on the cap analyzer, which unfortunately is missing from your microscope.
I thank Dr. Kile for this information.