Fig. 67.—Beck’s “New Fine Adjustment.”
To return to the fine adjustment of this, as of other forms of Messrs. Beck’s microscopes, the applied mechanism of which is believed to be one of the most sensitive and delicate character yet contrived. It is constructed as shown in the accompanying figure. The body of the instrument is supported upon the barrel D D; this barrel is accurately and smoothly fitted to the triangular core E E. At the top of barrel D D is screwed the cap G, to which is attached the rod C; this rod passes through the centre of the core E E and connects with the lever arm A at B. The action of the spring J, which is wrapped spirally around the rod C, raises the body of the microscope and holds the lever arm A tightly against the screw arm F. The slightest motion, therefore, of the screw F is communicated through the lever A and the rod C to the body of the microscope.
The great delicacy of this arrangement will be appreciated when it is noticed that the distance from I H is double the distance of I B, therefore any motion at B is only half that at H. This adjustment is one of the most delicate made for use with high powers.
Fig. 68.—Beck’s National Binocular Microscope.
In the construction of Beck’s Binocular National Microscope, the body is held in a sliding fitting in the limb, and is moved up or down by means of a rack and pinion motion. This constitutes the coarse focussing adjustment. The fine adjustment is effected by the milled head, which acts upon the body by means of a lever inside the limb. The upper circular surface of the stage is made of glass, and carries the object holder, which is provided with a ledge and spring to hold the object by means of the pressure of an ivory-tipped screw, so that it can be moved about readily and smoothly. The pressure of the screw is adjusted by the milled head, which permits of more or less pressure being made upon the edge of the object.
Fig. 69.—Beck’s Star Microscope.
When the stage is required for other purposes the object holder can be unscrewed and removed. Beneath the stage there is a cylindrical fitting for the reception of a diaphragm, a polariser, or other apparatus. The mirror, besides swinging in a rotatory semi-circle, is made to slide up or down the stem. The microscope is supported by a firm pillar on a tripod base, and the body can be inclined at any angle convenient for working. A sub-stage can be added at any time for the reception of an achromatic condenser fitted with concentric screws—a necessity for more delicate microscopical research work.