THE SUB-STAGE 



18 7 



stage ; the inner sliding plate is the essential addition to the usual 

 racked slide, in the application of the new fine adjustment to the 

 sub-stage. The range of motion is about ^th in. the difference in 

 radius between the smaller and larger ends of the steel cone. 



A very simple and practical device for the same purpose was 

 suggested by Mr. G. C. Karop, who knew that if the best possible 

 resolutions are required, the image of the flame given by the con- 

 denser should be as accurately adjusted in the focal plane as the 

 object itself. This arrangement of Mr. Karop's, admirably suited 

 to the stands of Messrs. Swift and Son, was patented by that firm. 

 It consists in the adaptation of their well-known 'climax' or 

 ; challenge ' fine adjustment to the slide carrying the sub-stage ; but 

 it is actuated by a milled head borne on the spindle to which is con- 

 nected the coarse rack motion. As will be seen in fig. 149, it is a 

 lever actuating a stud fixed to the Dovetailed slide which carries the 



FIG. 148. Fine adjustment to sub-stage. 

 Powell (1882). 



FIG. 149. Karop's fine adjustment for sub- 

 stage, made by Swift (1892). 



sub-stage. The extreme end of the lever is not acted upon by a fine 

 screw, but there is a cylindrical pin one end of which engages the 

 point of the lever, the other the face of the inner milled head ; the 

 milled heads resemble the Turrell stage arrangement, but the inner 

 milled head works on a screw on the stem of the outer milled head ; 

 when the inner milled head is turned it traverses the stem of the 

 outer one, and pressure by the S-shaped spring in the fig. causes the 

 stud to slowly raise or lower, as may be desired, the sub-stage which 

 carries it. One complete turn of the inner head presses the sub-stage 

 the T^th in. So that small fractions of this may be easily obtained, 

 and it is an advantage that the milled heads of both movements 

 are so close to each other. 



Messrs. W. Watson and Sons have also devised a useful arrange- 

 ment to serve the same end. As applied to their Yan Heurck 

 microscope it is shown in figs. 150 and 151. A is a controlling 

 milled head, B the lever which is seen from the side in fig. 150 



