MEDIUM MICROSCOPES 43 



adjustment is "of a lever pattern. There is a rack and 

 pinion for adjusting the tube-length. 



Microscopes of Medium Size. The most popular 

 microscopes are undoubtedly to be found among the 

 many excellent stands costing between 10 and 12, 

 designed generally on the same lines as the first-class 

 instruments of the same maker, but rather smaller and 

 simplified in mechanical details, in order to bring their 

 price down to a moderate figure. Taken as a group no 

 doubt need be felt as to their capacity to do good work 

 with the highest powers and most refined lenses, but the 

 wide tube and a few of the movements that make the 

 first group so advantageous for photomicrography are 

 omitted. 



Watson's Edinburgh Students' Microscope " H " (Fig. 

 18) is given as an example, and shows pretty well what 

 fittings may be expected on a stand of this group. It 

 is built somewhat on the lines of the Van Heurck, and 

 has a built-in mechanical stage, rack-and-pinion swing- 

 out and centring substage, and moderately wide tube. 



Students' Microscopes. A photograph of Bausch and 

 Lomb's " B.H." stand is given at Fig. 4 as an example 

 of the third group of microscopes. It has a plain stage 

 and screw-focussing substage, but with no arrangement 

 for centring the condenser. Stands of this class are 

 scarcely adequate for the most serious high -power photo- 

 micrography, but for medium and low-power work 

 they are satisfactory. The lack of centring mechanism for 

 the condenser is the most serious drawback. If such 

 a simple stand is bought, it is important to make sure 

 that a mechanical stage can be added later, and that 

 the stand is sufficiently stable, and accurate in its focus- 

 sing movements, to be worthy of additions. 



Most makers have a simple stand which corresponds 

 to this one, and more or less closely resembles their 

 better instruments in design. The cheapest form of 



