Large microscope on a double pillar with swinging substage, c. 1889
The accessories supplied with this microscope include three objectives marked 2/3, 1/6. and 1/12 immersion each with canister, two eyepieces, a substage condenser into which aperture stops can be inserted, and a double objective changer. Built into the stage is a wheel of apertures.
At the time this microscope was produced, it likely was the largest model microscope that Grunow offered. It measures about 17-inches in height inclined as shown in the photos. It is in the style of Zentmayer’s American Centennial model, incorporating most of the important features that characterize the latter model. Among these features are the mounting of the microscope on a double pillar attached to a calibrated rotating disk, a feature useful for measuring the angle of aperture of an objective. This Grunow instrument utilizes a Zentmayer type fine adjustment mechanism incorporating a lever embedded within the limb activated by a calibrated knob this allows much of the limb to remain stationary as the tube moves up and down. The microscope’s sliding brass and glass slide carrier is also reminiscent of those used on Zentmayer microscopes. The most notable Zentmayer innovation found on this Grunow microscope is the calibrated swinging substage. While Zentmayer was not the first manufacturer to incorporate a swinging substage, the main purpose of which was to allow oblique illumination, he popularized this innovation with the introduction of his American Centennial model in 1876. One feature possessed by this Grunow microscope, not found in Zentmayer’s Centennial model, is the rotating aperture disk embedded under the stage.
Evidently, the first known use of a swinging substage was with the microscope designed by Thomas Grubb in 1854. Several original examples of this microscope still exist, one of which is shown here. However, it was the introduction of Zentmayer’s American Centennial model in 1876 that spurred renewed interest in this feature. Almost immediately, other manufactures in America and England assimilated this feature into their designs. This feature was short lived however. By the turn of the century, with the ascendance of the Continental style microscope, it was realized that there were other simpler ways to achieve oblique illumination. See this series of articles that discuss the early microscopes having a swinging substage.
The Grunow brothers, Julius and William, emigrated from Germany to New York around 1849. They started in the scientific instrument business by first working for the optician Benjamin Pike of that city. By 1854, they began their own operation in New Haven CT where they concentrated on the production of microscopes. By 1864, they were back in New York. Some years later, the partnership ended. J. Grunow continued on to produce microscopes up to around 1892. The total output of the Grunows was limited in comparison to some other contemporary firms; on the basis of the observed serial numbers, they manufactured just over one thousand microscopes in total. See: a family history of the Grunows in 19th century America written by a descendant.
An advertisement from the Laboratory Handbook, 1885