ROSS—SMITH AND BECK. 
the entire body is moved to and from the stage. The object- 
piece is set in a tube, which moves within the principal tube of 
the body, the motion being imparted to it by a fine screw with a 
milled head, which constitutes the fine adjustment. Two dif¬ 
ferent kinds of stage are supplied, one called the lever stage, 
consisting of three plates of brass, the lowest of which is fixed, 
and the other two provided with guides and slides, and a lever by 
which they may be moved, together or separately, in directions at 
right angles to each other; the other form of stage also has two 
motions at right angles to each other, one produced by rack and 
pinion, and the other by a screw whose axis is carried across the 
stage, and is turned by the left hand, while the rack and pinion 
is turned by the right hand. 
85. Messrs. Smith and Beck also construct other forms of 
microscope, which, though perfectly efficient, are cheaper and more 
simple ; one of these is represented in fig. 42, p. 17. It is mounted 
upon a vertical pillar, supported on a tripod T ; the body of the 
microscope plays upon a cradle joint, to which the bent arm 
n u is attached ; the body of the instrument is moved by a rack 
and pinion in a triangular groove formed in the upper part of 
this arm; the coarse adjustment is made by the milled heads 
which move the entire body to and from the stage. In the 
lower end of the body, a tube is inserted, from which an arm 
projects, in which a fine screw plays, which is connected with 
another arm attached to the body of the instrument: by turning 
the milled head, a slow motion is therefore imparted to the 
tube thus inserted in the lower extremity of the body. In the 
•end of this tube the object-piece is set, so that the fine adjust¬ 
ment is made by this screw. 
To the lower end of the bent arm tj tt, the stage and its 
appendages are attached; two motions at right angles to each 
other are imparted to the stage, by milled heads; the reflector 
is mounted in the usual way, and provisions are made under the 
stage, by which achromatic condensers, polarisers, and other 
apparatus can be applied ; the disc of diaphragms is shown at L ; 
it is mounted on a short piece of tube, in which polarising and 
other apparatus may be inserted. 
86. Messrs. Smith and Beck supply with their best microscopes 
three eye-pieces and five object-pieces, the powers of which, as 
well as their angles of aperture, are indicated with their prices in 
the annexed table. 
