On a Microscope with Geometric Slides. By Keith Lucas. 277 



A few other points about the substage demand attention. The 

 position of the focussing screw (T, fig. 53), above the stage on the 

 right-hand side, is a very convenient one. Moreover, since the nut 

 in which the screw works is fixed to the stage, and the connection 

 between the screw and substage is flexible — being effected by a long 

 pointed pin which passes up inside the screw — alterations of focus 

 can be obtained without fear of any other derangement of the 

 illumination. 



The substage bracket is not a complete ring, as is the usual 

 practice, but a fork (S, fig. 52), open at the front. This enables the 

 centring ring to be readily removed. When in place, this ring is 

 held against its two centring screws by a spiral spring (W, fig. 49), 

 stretched between the two prongs of the fork. 



The range of the substage movement is amply sufficient to 

 enable it to take condensers of either the substage or understage 

 pattern. The absence of milled heads and slides below the stage 

 renders the condenser accessible from every side. 



Fig. 53. — Elevation : Microscope in Vertical Position. 

 Lettering as in figs. 49, 50, 51, 52. 



The advantages claimed for the instrument are the following : — 

 (1) Cheapness of manufacture, the turning of the tubes, and the 

 filing of the guides being less expensive work than the planing of 

 dovetailed slides. The alignment of the various slides also involves 

 very little expense, being obtained without careful workmanship. 



