Messrs. Baker’s Microscopes.
Of Messrs. Baker’s larger stands, the Improved “Nelson Model,” No. 2 ([Fig. 88]) stand is selected in preference to their more elaborate No. 1, and their simpler form, No. 3, as a high-class instrument, and one well suited for fine critical work; the former being somewhat better, only from having extra adjustments; the latter possessing no superior advantage over the “Advanced Students’” Microscope. This microscope is mounted on a solid tripod foot, which insures stability, whether placed in a vertical, horizontal, or inclined position; the front toes are slotted, so that they may be clamped to the base plate of a photo-micrographic apparatus, first introduced for photo-micrographic work, and will also be found convenient in ordinary work; as the fine adjustment milled head is placed at the bottom of the pillar, instead of at the top, the more usual place. For photo-micrographic work the advantage is that the strain of the pulley in such apparatus actuates the fine adjustment, and is less liable to cause vibration of the instrument. The advantage when the instrument is used for ordinary work lies in the fact that the weight of the hand is rested on the top of the tripod, thus admitting of steadier movement of the milled head. The fine adjustment is obtained by a “Campbell” differential screw, each revolution of which is equal to 1⁄200 m.m. The draw-tubes being graduated in m.m., allow of either short or long tube objectives being used, closing up to 150 m.m. and extending to 280 m.m., the rack and pinion adjustment to the lower tube affording a ready means of correction for cover-glass thicknesses. The eye-piece gauge, as will be seen from its dimensions, is of large size, being the same as that adopted by Zeiss for his long tube compensating oculars; smaller eye-pieces can, however, be adapted at any time.
Fig. 88.—Baker’s Improved “Nelson Model” Microscope. Dimensions.—Height when in vertical position and body racked down, 11′′; Height of stage, 41⁄8′′; Height of optic axis when in horizontal position, 8½′′; Spread of tripod foot, 8 × 8½′′; Diameter of mirrors, 23⁄8′′; Internal diameter of draw-tube, 13⁄10′′.
The mechanical rotating stage is divided on brass to 1⁄100 inch, with clamping bars and stop, by which a specimen can always be brought back to a certain position for registration. The sub-stage has rack-work focussing adjustment, and centring screws; a fine adjustment is added, if desired. On the whole, the instrument is suitable for special critical work, and is equally well suited for photo-micrography.
Fig. 89.—Baker’s Advanced Students’ Microscope. Dimensions.—Height when in vertical position and body racked down, 11¼′′; Height of stage, 4¾′′; Width of stage, 4′′; Height of optic axis when in horizontal position, 6½′′; Spread of foot, 6′′ × 6′′; Diameter of mirrors, 1¾′′; Internal diameter of draw-tube, 11⁄12′′.
Explanatory lettering of instrument: A, Huyghenian eye-piece; B, draw-tube graduated in millimetres; C, nose-piece; D, coarse adjustment; E, fine adjustment with millimetre screw; F, horse-shoe sliding stage, graduated with sliding bar in vertical and horizontal directions for use as finder; G, sub-stage rack and pinion screw; H and I, centring screws to sub-stage; J, carrier for condenser; K, mirror with movable arm supported on solid tripod foot.
The points of difference between this stand and the No. 1 model are that in the latter the fine adjustment carries the body only, and not the rack adjustment; the limb carrying both the body and the sub-stage is in one piece, giving, if possible, still greater rigidity; the rotation of the mechanical stage, which is divided on silver, is complete, and can be actuated by hand or rack work; it has a clamping screw and fine adjustment to sub-stage.
Baker’s Advanced Students’ Microscope ([Fig. 89]) may be described as a typical instrument, equally suitable for histological work and that of the advanced student. The intention of the maker in simplifying the adjustments and reducing the instrument in size, was to furnish a well-finished portable instrument at a moderate cost. This object has not been attained by supplying adjustments of second-rate quality, but by reducing their number to a minimum.
Fig. 90.—The Mayall Removable Mechanical Stage.
The tripod foot of the “Nelson Model” is replaced by a claw foot, which is in effect a tripod, as it rests on three points; it has not the same wide spread, but this, far from being a disadvantage, renders the instrument more portable. It has rack and pinion coarse and Campbell differential screw fine adjustments, draw-tube graduated in m.m., extending to 180 m.m., eye-piece gauge the same as the Continental size, large square open stage to afford the greater freedom of manipulation; sliding bar with graduations on bar and stage, which suffice for registering any given field under a low power; holes are also drilled in the stage ready to receive an attachable mechanical stage should it be thought advisable to add one at a later date. The sub-stage is of the universal size with rack-work focussing, adjustment, and centring screws.
Fig. 91.—Baker’s Model Histological Microscope. Dimensions.—Height when in vertical position and body racked down, 10½′′; Height of stage, 4′′; Width of stage, 3½′′; Height of optic axis when in horizontal position, 5¼′′; Spread of foot, 5¼′′; Diameter of mirrors, 15⁄8′′; Internal diameter of draw-tube, 11⁄12′′.
Messrs. Baker have recently introduced a similar instrument with swing-out sub-stage and adjustments for compensating for wear and tear of rack. The stage is also somewhat larger from back to front.
These stands are very suitable for bacteriological research, and for amateurs wishing to obtain a stand which will carry all the apparatus they are likely to need, without going to the expense of the larger models, no better instrument could be desired.
Their “Removable Mechanical Stage” ([Fig. 90]) is a modification of the pattern designed by the late Mr. J. Mayall. The vertical movement is by rack and pinion, giving a range of 11⁄8 inch. The horizontal motion of 1½ inch is accomplished by means of a quick-acting screw. The object is pressed tightly to the stage of the microscope by means of three points, and the whole of the mechanical part is firmly clamped by two thumb screws which can be readily removed. The stage is made to carry slides of any size less than 1¾ inch wide.
Baker’s Histological Microscope ([Fig. 91]) is of a different type to the preceding, and is intended to represent one of medium power, affording magnification of about × 400 as a maximum. It is supplied with a diaphragm beneath the stage, without other illuminating apparatus than that of the mirror. But if the adjustments of such a stand are good, there is no reason why some form of sub-stage condenser should not be added, to make the instrument somewhat more serviceable. There is, however, a rather too limited space beneath the stage of an instrument of this kind to admit of a sub-stage condenser, consequently it cannot be said to be suitable for critical work. For all ordinary students’ work this microscope is certainly available.
Fig. 92.—Rousselet’s Tank Microscope.
The stand of the Model Histological Microscope has the same form of foot as the more advanced student’s stand. It is somewhat lighter, and more portable, a matter of consideration in a student’s microscope, which often has to be carried to and from a class-room. It is provided with rack and pinion coarse adjustment, and a Campbell differential screw fine adjustment, draw-tube, and diaphragm; the diaphragm carrier being of the universal size, so that it can be replaced by an Abbe condenser at any time. With the additions suggested, this instrument can be made equal to those of a higher standard.
Rousselet’s Tank Microscope ([Fig. 92]), for rapidly looking over pond water and weeds, consists of a jointed arm moving parallel to the side of the tank to carry an aplanatic lens; the arm is focussed by means of rack and pinion fixed to the upright of a mahogany stand, upon which the tank can be placed, or it can be clamped directly to the tank by means of a screw. This handy form of pond microscope is made by Messrs. Baker.