Continental Microscopes.
Continental Microscopes.—The better known among continental opticians are Zeiss, Leitz, Seibert, Reichert and Hartnack. All seem to have vied with each other in the attainment of perfection in the manufacture of the most useful forms of microscopes. The late Carl Zeiss did more for the modern microscope than either of the opticians referred to above. I therefore take a medium typical model of his from a long series of highly-finished instruments for my illustration. Zeiss’s successors have of late endeavoured to perfect the mechanical details of their instruments in three or four directions, i.e., fundamental features of the stand, stage arrangements, means of focussing, and illumination.
The Stand.—The general form of the stand still partakes too much of the original sameness of type introduced by Oberhäuser, and modified and improved by Hartnack; the “Babuchin” stand being still in favour with some few makers. The greater firmness and steadiness of Zeiss’s stand ([Fig. 95]) is secured by the horse-shoe form of foot, which, for the most part, is massive and well adapted to carry the stout uprights, which support a well-balanced, substantial body-tube and a graduated draw-tube, circular stage with a vulcanite disc, 4 inches in diameter; a sub-stage with centring arrangement for Abbe’s illuminating apparatus, and iris diaphragm and other diaphragms for use when the condenser is thrown aside. The mirror is full-sized, plane and concave. The coarse adjustment is regulated by a rack and pillion movement so perfect that objectives of medium power can be focussed by it alone. The fine adjustment is made by micrometer screw, the force exercised by which is transferred to the movable body by a single contact between two hardened steel surfaces. This ensures extremely delicate and uniform motion of the body which carries the tube.
The divisions in the milled head of the screw furnish a means for the registration of the vertical movements of the tube. In the latest stands, each division corresponds to an elevation or depression of the tube in the direction of the optic axis of 0·01 mm. By this means measurements of thicknesses may be made with a considerable degree of accuracy, the upper and lower surfaces of the object being successively focussed, and the amount read off on the milled-head, by the fixed index. In doing this, care must be taken to make both adjustments by a rotation of the screw in the same direction. The thickness of an object in air is then equal to the difference between the two readings. By this means the thickness of any other substance may be measured—that, for instance, of the cover-glass of the object.
Fig. 95.—Zeiss’s Medium Stand Microscope.
The medium tube-length of the microscope is 160 mm. from the attachment of the objective to the eye-piece end. The draw-tube admits of the length being increased or diminished, and this may be read off by means of the millimetre scale engraved on the tube. My description of this model also applies to the higher class microscopes, which will be found in every way well finished and adapted to biological and scientific research.
Fig. 96.—E. Leitz’s Medium-sized Microscope.
E. Leitz’s of Wetzlar Microscopes.—This optician publishes a series of twelve high-class forms of instruments. By preference, the horse-shoe form of stand ([Fig. 96]) is adopted in the whole of this maker’s models, the body being supported on a hinge joint and clamped over, and fitted with a circular revolving centred mechanical stage, attached to the ordinary stage by means of a set pin, which fixes the stage in position. By removing the screw, the stage can be detached; in this way, the stage serves for searching over large surfaces and registering the results.
Fig. 97.—Leitz’s Dissecting Microscope.
The coarse adjustment is made by rack and pinion, and the fine adjustment by micrometer screw, the head of which is provided with a scale reading 1⁄100 mm. The draw-tube is also cut and ruled to millimetre scale. The sub-stage has rack and pinion movement, and is arranged for the Abbe condenser and iris diaphragm. This is attached to the upper stage by means of a set pin, which fixes and retains it in position after perfect centring. By removing the pin, the sub-stage can be either detached or swung aside by pressing a button. In short, this microscope is in all respects well furnished and fitted with the requisite complex mechanism necessitated by modern high-class technicological work.
Leitz’s students’ microscope, with sliding body, micrometer screw fine adjustment, concave mirror, two eye-pieces and two objectives, ¾ inch and 1⁄8 inch, in mahogany case, costs £3 10s. Leitz’s dissecting microscope, with a heavy foot and rests, is fitted with two aplanatic lenses, magnifying × 10, × 20 diameters.
Reichert and Seibert adhere to the same model as that of Zeiss, and therefore require only a brief notice. Their microscopes are characterised by substantial workmanship, suitable construction, and exact centring. The coarse adjustment is obtained in the usual way by rack and pinion, the fine by micrometer screws, which work easily, and are protected against wear and tear by having their working surfaces hardened. The stands of the better class instruments have micrometer screws graduated, and draw-tubes cut to millimetre scale. Their mechanical stages and sub-stages and accessories are in every way well finished; stage forceps, tests, and an assortment of cover glasses and slides being added. Their first-class microscopes are sent out in mahogany boxes.
On going through the continental makers’ catalogues, it will be noticed that their well-equipped microscopes are rather more costly than that of their English confreres. It is understood Messrs. Baker and Watson are the constituted agents for these opticians.
Nachet’s Microscope, a new form of which was first seen at the Antwerp Exhibition 1892, is very solidly built, and has all the qualities necessary for histological work. The stage rotates about the optic axis, and carries a movable slide holder. The coarse adjustment is by rack and pinion movement, the fine by the new system of micrometer screw (described in the journal of the Royal Microscopical Society of 1886), with divided head indicating the 1⁄400 part of a mm. The plane and convex mirror is mounted on a jointed arm. The draw-tube is divided into millimetres. The illuminating system, consisting of a wide-angled Abbe condenser (N.A. 1·40) with iris diaphragm, is raised or lowered by rack and pinion screws. The iris diaphragm, being mounted on a wheel, is worked by a tangent screw, which by a very slight movement causes the aperture of the diaphragm to pass from the centre to the periphery of the condenser. Altogether the arrangement of the sub-stage is novel, and the instrument is extremely well arranged and adapted to modern requirements.
Nachet and Hartnack, of Paris, hold an almost equal rank as makers of first-class microscopes, and in point of excellence of workmanship fairy rival those of our English makers.
Fig. 98.—Nachet’s Class Demonstrating Microscope.
There are very many other London and Continental makers of microscopes besides those especially mentioned, who have well-sustained reputations as opticians, and who, from want of space, I have been obliged to pass over. Messrs. Newton’s Students’ Microscope must be mentioned with respect. It is a good and useful instrument, has a firm stand with a reversible (rotatory) body movement, which seems to ensure steadiness when brought into the horizontal position for micro-photographic purposes. There are other opticians whose microscopes have stood the test of time—Messrs. Collins, Crouch, &c. It may, however, be taken as a well-established fact that those opticians known to manufacture the more highly-finished models also produce the more serviceable forms of students’ class-room, and other microscopes.