Messrs. Beck’s Microscopes.
Messrs. Beck have adopted what may be termed a rival system of fine adjustment in their modern microscopes. The short lever and screw applied externally to the body tube is peculiar, I may say, to the Ross-Jackson system, and was originally devised to allow of the body tube being supported somewhat more firmly on the limb. This change had its merits fully realised in the early microscopes of Smith and Beck. To their successors, R. & J. Beck, the microscope owes much, and very many important improvements, while all their instruments and accessories are excellent examples of good workmanship and finish. In their Pathological Microscope we have a movement originally found in Tolles’ microscopes: a vertical disc, by which the centre can be raised or depressed to correspond with the thickness of the slide. The stage can also be brought into an inverted position by rack and pinion. Their fine adjustment has been greatly improved, as we shall presently see, whereby it has been made more sensitive and delicate of adjustment. The general construction of their microscopes as a rule possess the following advantages: the stands are strong, firm, and yet not too light or too heavy, the instruments cannot alter from the position in which they are placed, as, unfortunately, will occasionally happen when joints work loose; in every position the heavier part of the stand maintains the centre of gravity.
Beck’s Pathological Microscope ([Fig. 65]) is a nearly perfect instrument, furnished with a firm triangular foot, which ensures great steadiness in any position. It has a well adapted joint for placing the instrument at any angle of inclination; coarse adjustment by spiral rack and pinion; fine adjustment by delicate lever and micrometer screw motion; rack and pinion focussing and screw centring sub-stage, made to carry all condensers and other sub-stage apparatus; mechanical stage with horizontal and vertical traversing motions. The stage is attached to the instrument by two screws and can therefore be removed at pleasure, leaving a large square flat glass stage for the culture-plate. It is likewise provided with finder divisions, and as it always fits on to the same place, any particular portion of the object can be recorded and found at any moment. The triple nose-piece is a convenient addition, and a very acceptable one to the student while diligently engaged in histological research.
Fig. 65.—Beck’s Pathological Microscope, with square and removable stage.
Fig. 66.—Beck’s Large “Continental Model” Microscope.
Beck’s Large “Continental Model” Microscope is of superior finish. It is provided with a substantial horse-shoe foot, which gives support to the strong, well-balanced body, jointed for giving the microscope any angle of inclination. The body is provided with a draw-tube which can be racked down to the Continental measurement. It has a spiral rack and pinion coarse adjustment, and a fine adjustment of the most perfect workmanship, which will be described in detail presently. It has a large square stage with vulcanite top plate to receive culture preparations. The sub-stage is of the most approved form for centring, and carries an achromatic or Abbe condenser, iris diaphragm, &c. The double mirror can be swung out of place for direct illumination and micro-photography. Altogether, this instrument is in every way fitted for critical or class-room work.
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.
Beck’s Star Microscope is in every sense a students’ or class-room instrument. It is firm and well made, with joint for inclination, large square stage, sliding coarse adjustment and fine adjustment by micrometer screw, draw-tube, iris diaphragm, double mirror on swinging crank arm, A or B eye-piece, a one-inch and quarter-inch objective, the magnifying power of which ranges from 38·5 to 183.
Fig. 70.—Beck’s Binocular Dissecting Microscope.
An early binocular microscope for dissecting purposes was devised by the late Mr. R. Beck. ([Fig. 70].) This took the form of a simple instrument built up on a square mahogany base A raised about four inches upon four brass supports B B, having a large circular stage plate made to revolve on a second plate, on which the object is placed and brought under the eye for dissection. On the left hand side is a milled head rack and pinion K, which acts upon a horizontal bar I for focussing the magnifying lens. Another bar, R, carries the prism P and a pair of eye-pieces arranged on the principle of M. Nachet’s binocular microscope. Mr. Beck preferred to adopt Wenham’s method of arranging these prisms; that is, by allowing half the cone of rays to proceed to one eye without interruption, while the other half is intercepted by the prisms and transmitted to the other eye. Beneath the stage is the ordinary mirror L. The condensing lens M is supported on a separate brass holder let into one of the supports of the stand. In practice, however, this arrangement was found inconvenient, and the microscope has therefore not been brought into general use.