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.
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.
figure 3
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.
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