74: 



THE MICROSCOPE AND ITS REVELATIONS. 



PIG. 52. 



as also to the due balancing of the weight of its different parts upon the 

 horizontal axis. Any inclination may be given to it; and it may be fixed 

 in any position by a clamping screw, turned by a short lever on the right- 

 hand upright. The 'fine' adjustment is effected by the milled-head on 

 the transverse arm just behind the base of the ' body;' this acts upon the 

 'nose' or tube projecting below the arm, wherein the objectives are 

 screwed. The other milled-head, seen at the summit of the stem, serves 



to secure the transverse arm 

 to this, and may be tightened 

 or slackened at pleasure, so 

 as to regulate the traversing 

 movement of the arm; this 

 movement is only allowed to 

 take place in one direction, 

 namely, towards the right 

 ride, being checked in the 

 opposite by a ' stop,' which 

 secures the coincidence of 

 the axis of the principal 

 'body' with the centre of 

 the stage, and with the axis 

 of the illuminating appa- 

 ratus beneath it. The ob- 

 ject-platform, to which rect- 

 angular traversing motions 

 are given by the two milled- 

 heads at the right of the 

 stage, is also made to rotate 

 in the optic axis by a milled- 

 head placed underneath the 

 stage on the left-hand side; 

 this turns a pinion which 

 works against a circular 

 rack, whereby the whole 

 apparatus above is carried 

 round about two-thirds of 

 a revolution, without in the 

 least disturbing the place of 

 the object, or removing it 

 ROSS'S First-class Microscope. from the field of the Micro- 



scope. The graduation of 



the circular rack, moreover, enables it to be used as a Goniometer ( 92). 

 Below the stage, and in front of the stem that carries the mirror, is a 

 dovetail sliding-bar, which is moved up and down by the milled-head 

 shown at its side; this sliding-bar carries what is termed by Mr. Ross the 

 'Secondary stage 5 (shown separately at B), which consists of a tube for 

 the reception of the Achromatic Condenser, Polarizing prisms, and other 

 fittings. To this secondary stage a traversing movement of limited extent 

 is given by means of two screws, one on the front and the other on the 

 left-hand side of the frame which carries it, in order that its axis may be 

 brought into perfect coincidence with the axis of the body; and a rotatory 

 movement also is given to it by the turning of a milled-head, which is 

 occasionally useful, and the exact amount of which is measured by a 

 graduated circle. The special advantages of this instrument consist in 



