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IV . — A Microscope with New Focussing Mechanism. 
Designed by Keith Lucas. 
( Read 21 st December , 1898 .) 
The instrument of which a representation is given in figs. 27, 28, was 
constructed primarily with a view to steadiness and rigidity. It was 
partly for this object that a system of focussing the body-tube and 
substage was adopted, which effected both coarse and fine adjustments 
in each case by means of a single planed slide. It will be seen that 
the consequent reduction of planing is likely to affect also the cost of 
production of the instrument. 
Fig. 27 . 
The novelty of the instrument consists essentially in the mecha- 
nical arrangement of the coarse adjustments of the body- tube and 
substage. 
The fine adjustment is effected in the way common to many 
modern instruments. A lever A (fig. 27), contained in the main 
casting or “ limb,” engages at one end C with the body-tube B, while 
the other end is controlled by a micrometer screw D. The fulcrum E 
L 2 
