84 PRACTICAL TREATISE ON THE MICROSCOPE. 



MR. ROSS'S PORTABLE ACHROMATIC COMPOUND 

 MICROSCOPE. 



This instrument is represented by fig. 45, and, like the 

 larger one, is supported on a firm tripod base, a, from which 

 rise two strong uprights, h, supporting at their upper parts the 

 trunnions to which the square frame, c, carrying the stage and 

 the tube, d, are attached. Within the tube, d, a smaller tube 

 is made to slide up and down by rack and pinion, the former 

 is seen at n, the latter being turned by the milled head, o; 

 this forms the coarse adjustment. To the upper part of the 

 inner tube a very stout arm, e, is attached by the screw, f, on 

 which the arm may be turned ; into the opposite end of the 

 arm, the compound body, g, is screwed. The fine adjustment 

 consists of a conical-pointed steel screw pressing against the 

 top of a slit in an inner tube, to the end of which the adapter 

 for receiving the object-glasses is fixed. The stage has the 

 usual rectangular motions, that from the side being performed 

 by a screw and nut, by tiu-ning the milled head, i, whilst the 

 up and down movement is effected by rack and pinion, by 

 turning the milled head, h. The stage-plate is provided with 

 a sHdiog-rest, I, by which the distance of an object from the 

 central hole in the plate may be regulated before focussing ; 

 this answers the purpose of the complicated sliding frame in 

 the more expensive instruments. At the upper part of this 

 stage-plate there are two holes for the reception of the forceps 

 and side refiector. To the under part of the stage the achro- 

 matic condenser, the diaphragm-plate, the dark wells, and 

 polarizing prism, may all be adapted as in the larger instru- 

 ments ; and, for convenience of package, the stage itself may 

 be turned on a pivot, so as to be at right angles with the 

 tube, d. The mirror, m, is mounted in the usual manner, and 

 is capable of being raised up or down the tube, d, on which it 

 is supported. 



This stand, like the preceding, is constructed on a plan 

 ascertained by Mr. Ross, after a lengthened series of investi- 

 gations, to be the most steady, and is particularly to be 

 recommended to those whose means are limited, in conse^ 



