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.
Messrs. Watson’s Microscopes.
Among London opticians, the various microscopes manufactured by Messrs. Watson, of Holborn, are of high finish and good workmanship. Those specially designed for the use of students possess merits of their own in their mechanical construction, and also embody a provision, as indeed do all their instruments, whether for students or more pretentious work, whereby wear and tear in their frictional parts can be compensated for by the user himself. This is effected in a simple but efficient manner. The fittings are sprung, and screws set just outside the dove-tails. The very slightest turn of the screws compresses the dove-tails, and a very large amount of wear can in this way be prevented.
I am glad to notice that Messrs. Watson have adopted certain standard sizes recommended some time ago by the Royal Microscopical Society for the diameters of eye-pieces. It would be a great advantage if the same standard became generally recognised and brought into use, since it is a matter of much importance to microscopists.
Watson’s Edinburgh Students’ Microscope ([Fig. 71]) is a thoroughly efficient one for all practical purposes, great care having been bestowed upon its smallest details, and it is not difficult to perceive the reason of its popularity among students. The tripod form of foot ensures great steadiness and firmness; the body carries the smaller 0·92 eye-piece, and with draw-tube closed is of the Continental length. The draw-tube is graduated to millimetres, and when fully extended the body measures 10 inches. The stage is provided with mechanical and rotary movements; the compound sub-stage with centring screws, rack and pinion to focus, and a means of lifting the condenser out of the optical axis when not required for use. Notwithstanding, none of the movements are at all cramped; a clear distance is maintained beneath the stage, affording plenty of room for manipulating the mirror. Both coarse and fine adjustments work with smoothness, the latter being on Watson’s latest improved principle—one revolution of the milled head moves the body 1⁄300 of an inch. The stage is of extra large size, to allow of the use of large culture-plates. No Continental stand of higher price compares with the Edinburgh microscope. Its height when placed in the vertical position is 11½ inches.
Fig. 71.—Watson’s Edinburgh Students’ Microscope.