Some Early Microscopes from the Optical Institute in Wetzlar

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Certainly, most microscope collectors are familiar with the firm E. Leitz, Inc. and many of them probably have several Leitz microscopes represented in their collection. Some, however, may not realize that the founder of the firm was not Ernst Leitz I, but Carl Kellner. Kellner founded what was named the Optical Institute in Wetzlar Germany in 1849. By 1851 he employed twelve workmen and was producing his first microscopes. Among the more notable graduates of the Institute was one, Ernst Gundlach, familiar as the designer of the first Bausch & Lomb stands, who was employed during the years 1859-1862.1 Other opticians who at one time worked at the Optical Institute and later founded their own firms include Riechert and Hensoldt.2 Kellner's microscopes met with wide acclaim and were furnished with his noted invention, the orthoscopic eyepiece. While first applied as an eyepiece for telescopes and then later adapted to the microscope, it enables a large flat field of view.

Unfortunately, at only the age of twenty nine, Kellner succumbed to tuberculosis in 1855. The Optical Institute survived under the leadership of Friedrich Belthle, an apprentice of Kellner's, who married Kellner's widow shortly after his death. In 1863 Ernst Leitz joined the Institute. By 1865 he was a partner in the firm, and later became the sole proprietor after Belthle's death in 1869. For some biographical information about Carl Kellner, link here. In the pamphlet Leitz Microscopes for 125 Years3, it is mentioned that during this early period of the Optical Institute under Kellner's and Belthle's leaderships, at least three different models of microscopes were manufactured. Some details about these instruments can be gathered from the information contained in the price lists that were issued over the years. Links to copies of these lists are provided at the end of this article. For some years, I have had one of these microscopes represented in my collection. More recently, I was fortunate in obtaining several others. I was able to locate an additional example in the possession of a fellow collector. Since, as far as I can tell, descriptions of these early Wetzlar microscopes can not be found in the usual sources, I thought that others interested in the history of the microscope might be interested in learning about them.

Assigning dates to the microscopes that will be discussed herein was made possible using information contained in the aforementioned Leitz pamphlet that has a table giving the average number of microscopes manufactured during ten year intervals starting in 1851. These data were plotted for the years 1851-1870. The best linear relationship was found and then integrated giving a binomial expression that correlates the serial numbers with the dates of manufacture. It should be noted that the serial numbers found on the later Leitz microscopes derive from the same series as these earlier Kellner and Belthle stands.

One of these microscopes is shown in Figure 1. It is the most elaborate both in terms of the accessories associated with it and its mechanical movements and it probably represents the top of the line in the series. In the 1862 price list, this model is referred to as the "Grosses Mikroskop". The microscope is signed on one side of the limb "C. Kellner in Wetzlar"and on the other "Belthle and Rexroth, No. 451". It was made in 1861. Following the death of Kellner in 1855 and beginning in 1857 there was, for a brief time, a partnership between Belthle and H. Rexroth.2,4 Whatever happened to Rexroth and in what manner he continued in the microscope business after the partnership dissolved remains unclear although there exists in another collection a microscope signed only by Rexroth that shows similarities to one of Kellner models.

 

As shown in the figure, the microscope is 12 inches in height. The oval base with squared off sides is machined iron painted black. Inset into the base is an iron ring to which is attached the main body of the microscope. This ring can freely rotate within the base so that the microscope is capable of full 360° rotation. The single sided concave mirror is attached to a arm with a swivel joint that allows lateral side to side adjustment of the mirror's position. The mirror remains stationary during rotation of the microscope. The brass limb moves on a steel triangular shaft with inset brass rack. A brass plate engages the pinion of the coarse adjustment to the rack and has adjustment screws that allow the tension between the pinion and rack to be varied. The fine adjustment is by micrometer screw that is located at the rear under the stage. There is an adjustment screw that will allow any excess play of the fine adjustment to be taken up. The rectangular stage has an oxidized brass finish there are no provisions for stage clips. Inset under the stage is a wheel with five apertures. An accessory substage apparatus slides into a dovetailed fitting under the stage. This apparatus holds an aperture stop which can be moved up or down relative to the specimen by means of a lever. The microscope is cased with a number of accessories that include three eyepieces numbered I-III and five objectives numbered 0, 1, 7, and two 3's. The 0, 1, and one of the 3 objectives are signed "Belthle & Rexroth". The number 3 objective is now defective (its front element is now mounted backwards!) and it was presumably replaced by the original owner with another number 3 signed "Belthle". The number 7 objective is unsigned but is engraved with the number "1337" this lens appears to be a later addition although it has the same non-standard thread as the other objectives. Also included is a substage Nicol prism that mounts onto a dovetail slot located on the mirror arm and an analyzing prism that mounts within the body tube by screwing into the back of the nosepiece.

The next model is shown in Figure 2. The microscope is signed on one side of the limb "C. Kellner's nachfolger" and on the other "FR. Belthle in Wetzlar, No. 945" "nachfolger" can be translated as "successor". This stand is dated to 1866. In the 1866 price list, this model is referred to as the "Kleines Mikroskop". It is 12.25 inches tall as shown in the figure. The round iron base is painted black and is 3 and 3/8 inches in diameter. A short iron pillar rises from the base and engages a short oxidized brass arm that supports the main body of the microscope. This arm can freely rotate about the base so that the microscope is capable of full 360° rotation. The single sided concave mirror is attached to a arm with a swivel joint that allows lateral side to side movement of the mirror. The coarse adjustment is by push tube. The outer tube is sprung and contains an adjustment screw that allows the tension to be altered. The fine adjustment mechanism is identically constructed as in the previous example. The round stage has an oxidized brass finish. There is no provision for stage clips. Inset under the stage is a wheel with five apertures. The microscope has no provision for an additional substage apparatus.

C. Kellner in Wetzlar Belthle and Rexroth, No. 451

figure 1

for additional photos, click on the above image

C. Kellner's nachfolger FR. Belthle in Wetzlar, No. 945
figure 2

    for additional photos, click on the above image

The microscope was found cased with three eyepieces numbered I, III, and V and four objectives the number 1 is signed " B.L.", the numbers 3 and 7 are signed "Belthle & Leitz", and the number 4 is unsigned. Also found with the microscope is a hand written magnification chart listing the various magnifications obtained using the different combinations of eyepieces and objectives. As stated above, this microscope could be dated to 1866 from its serial number. It was in the previous year that Ernst Leitz became a partner in the firm. From the signatures on the microscope and the objectives, it would seem that the microscope was made immediately before Leitz became a partner while the objectives were made after this event. It is therefore likely that this microscope, with its associated objectives, is one of the first articles of commerce bearing the Leitz name. Represented in this collection is another example of this model having a different selection of optics and a different layout within the wood storage case.

 

Another instrument is shown in Figure 3 and it is the simplest of the models described in this article. The microscope is signed on one side of the limb "C. Kellner's nachfolger" and on the other "FR. Belthle in Wetzlar, No. 895". It can be dated to 1864. In the 1866 price list this is referred to as the "Kleines Mikroskop, Neues Modell". It is 11.5 inches tall as shown in the figure. The square iron base is painted black and has an attached short iron pillar that supports the main body of the microscope. This model does not have any provisions for rotation about the optical axis. The single sided concave mirror is attached to a short arm mounted below the stage. The coarse and fine adjustments are constructed in an identical manner as in the previous example. The square stage has an oxidized brass finish there are no provisions for stage clips. Inset under the stage is a wheel with 6 apertures. The microscope has no provision for an additional substage apparatus. This microscope was also found with its case and a number of objectives and eyepieces. The objectives represented are numbers 1 and 3 signed "FR. Belthle" , and a number 0 signed "FR B". The three eyepieces are numbered I, II, and III.

The final model is shown in figure 4. It is signed on one side of the limb "C. Kellner in Wetzlar"and on the other "Belthle & Rexroth, No. 280". It dates from 1859. In the 1858 price list, this is referred to as the "Mittleres Mikroskop IIa ". As shown, it measures about 12 inches in height. The focusing adjustments are as already discussed in the descriptions of the other models. This microscope is equipped with eyepieces I and II and the objectives 1, 2, and 3 which are signed "Belthle & Rexroth". Among the accessories is an articulated arm with ball and socket joints that fits into a hole in the base which might have held a stage condenser (now missing) or something else? Also, there is a Nicol prism in a brass holder that mounts behind the nosepiece. In contrast to some of the other microscopes discussed herein, this instrument does not rotate upon its base, but instead has an upper rotating stage plate. Below the stage is a rotating diaphragm with 7 apertures.

Overall, these microscopes were extremely well constructed. The mechanical movements are still smooth and without lost motion. Most commendable in each of these models was the incorporation of various adjustments to the focusing mechanisms that could compensate for wear. Such adjustments were usually absent in contemporary microscopes and in many that came later.


References:

1. Warner D. J., Ernst W. Gundlach German-American Optician, Rittenhouse, 1, 10, 1995.
2. Dipple L., Das Mikroskope, F. Vieweg und Sohn, Braunschweig, 1882.
3. Grehn J., Leitz Microscopes for 125 Years, E. Leitz Inc., Rockleigh NJ, 1977.
4. Nowak H. P., Geschichte des Mikroskops, Zürich, 1984.

I am interested in adding additional antique microscopes to my collection. You can get more information about these antique microscopes by visiting my web site.

Bausch & Lomb Physician's Model. C. 1876

    C. Kellner's nachfolger FR. Belthle in Wetzlar, No. 895

    figure 3


    C. Kellner in Wetzlar, Belthle & Rexroth, No. 280, c. 1859

    figure 4

    for additional photos, click on the above image

     

     

 

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