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 

 IT 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 u, 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. 



83 



