DESCRIPTION:
This compound petrographic microscope is signed on the side of the foot: VOIGT & HOCHGESANG, GÖTTENGEN. The foot of the microscope and the case both have a painted number 10 reflecting use in a teaching institution, but the case is not original to the microscope, being a circa 1895 case by Leitz (thanks to Dan Kile for pointing out the maker of the case!)Although the case is not original to the microscope, it is from about the same time period, and its number lends support to the notion that although not original, it was the case used to store the microscope at the teaching institution that this microscope was likely used at. I include it on this web page because of its provenance.

The microscope is finished in lacquered brass for the pillar and limb, and the sides of the foot. There is an oxidized flat blue-black finish for the top of the foot, and the center of the stage. There is a nickeled finish to the scale of graduations for the periphery of the top of the rotating stage, the fine focus graduations, and the graduations on the polarizer.

The stage is graduated from 0 to 360 degrees, marked each degree and labeled every ten degrees, but with a Vernier scale enabling readings to fractions of a degree. There are two holes in the stage for stage clips. The central blackened part of the stage is graduated in two directions, oriented 90 degrees from one another, allowing a slide to be relocated to a specific position of interest.

Coarse focus is by sliding the main optical tube and there is also a draw tube. There is a disk-shaped flange at the top of the drawtube to support an over-the-eyepiece analyzer, but the microscope is missing the original analyzer which would have been mounted in a graduated, part cylindrical, part conical nickel housing. The otherwise unlacquered main optical tube has a narrow lacquered brass bar that guides the tube in an opening of the ring on the arm of the limb, preventing it from rotating. The draw tube has the same kind of arrangement. These arrangements, along with the slot which keeps the eyepiece in the same orientation, would have maintained the orientation of the cross hair in the eyepiece.

Fine focus is by a finely threaded screw with a brass knob at the top of the continental limb. The fine focus knob also has nickel calbrations on its periphery.

A substage polarizer assembly slides into a dovetail slot in the bottom of the stage. The calcite Nicol prism polarizer is mounted in a nickel cylinder which rotates inside a second nickel cylinder. The inner cylinder, housing the prism is graduated from 0 to 360 degrees, in 5 degree increments, labelled every 20 degrees. The outer cylinder has a short blackened rack attached, allowing rack and pinion focusing for this substage polarizer. The pinion is controlled by a knurled brass knob.

The limb has a triangular profile. There is one eyepiece with a registration screw to fit it into the small slot at the top of the drawtube to maintain the orientation of the cross hairs that would have been in the eyepiece originally. There is a single high power divisible objective with a female thread that fits the male thread on the nosepiece.

Immediately above the place where the objective screws in to the nosepiece is a slot for the introduction of wave plates. This slot, shown to the left, has a sliding collar to cover it when not in use. Immediately above this slot is the adjustment screw for right-left centering; the knob of this screw is missing. The knob for centering forward and backward is on the front of the tube at the same level.

The substage mirror has both flat and concave sides and is mounted in a gimbal to the swinging tailpiece. The mirror assembly attaches to a slot in the tail piece so it can be moved up or down on the tailpiece, secured in the desired position by a locking knurled knob.

There is a single eyepiece which had cross hairs used for centering the nosepiece in the optical axis, but the cross hairs are now is missing. It is optically sound.

There is a single divisible objective. The uppermost element is labeled 4 but the other elements have no visible numbers. This objective functions well, though the elements are not easily separated from each other.

CONDITION:
The microscope is in working condition. The lacquered brass has fine scratches and small areas of lacquer damage on the back of the limb. The arm and ring have mostly good laquer but with some tiny areas of lacquer loss and one bigger area of loss on the back of the ring. The nickeled graduations are all easily readable. The graduated nickel on the stage and fine focus knob has some pitting to the finish. The finish of the center of the top of the fine focus knob is completely lacking, but most of its underside has preserved lacquer. The support ring at the top of the drawtube has areas of lacquer loss and tarnish. The mirrors are pitted at their periphery but function well. All parts of the microscope function as they should, but it is difficult to rotate the polarizer in its housing because the grease has dried up. Likewise the divisions of the objective cannot be unscrewed, though the entire objective can be removed from the nosepiece. The foot has some scratches to the oxidized finish and the lacquered brass of the foot has minor losses to the lacquer. The stage finish was worn and damaged, and has been cleaned and partly refinished appropriately. There are no additional eyepieces or objectives.

There are no waveplates with this example, and the original over-the-eyepiece analyzer, an example of which from a different microscope is shown to the left, is missing. As is the case with most microscopes by this maker, the serial number is not engraved on the microscope, and may have been engraved on the polarizer. The case that this microscope was stored in is not original and was most likely by Leitz. The case has cracks and is missing about a 1/4 inch part of the door on the side that would have been attached to the hinges. The eyepiece previously had cross hairs, but these are now lost. One of the centering knobs for the nosepiece apparently broke off in the past, the other is present and functions as it should.

HISTORY OF VOIGT & HOCHGESANG MICROSCOPES:
Voigt & Hochgesang were famous for selling petrographic microscopes and especially petrographic thin section slides, some of which are shown to the left. V & H made several different models, some of which, from a 1900 publication*, are shown here: Their microscope business was apparently absorbed by Steeg & Reuter in 1905 thus this microscope might be earlier than 1905. It is notable though, that their petrographic microscopes are still pictured in a book on petrography published in 1912. V & H continued to make slides until 1915. Petrographic microscopes of this firm are very rarely seen today, and their slides are often sought after by collectors.

For a review of the firm's history please see the review by Yuval Goren.

The author is grateful to Dan Kile and Joseph Zeligs for editorial help and suggestions for this webpage.

*Die mechanischen Werkstatten der Stadt Göttingen, pp121-127, 1900.