THE MECHANICAL STAGE 27 



The Mechanical Stage. A mechanical stage is not at 

 all an essential, although of great convenience for search- 

 ing a slide, and for accurately placing the part to be 

 photographed in the most suitable position in respect to 

 the dimensions of the plate. For the latter purpose a 

 rotating stage is exceedingly useful, and indispensable 

 for petrology. Verniers or scales on the stage movements 

 are most useful for recording the position of any par- 

 ticular spot on a slide that may be required for future 

 reference with high-power objectives. But with all its 

 convenience a mechanical stage is far better dispensed 

 with than other parts of the microscope to be mentioned, 

 and if its addition involves the purchase of a . less ac- 

 curately finished instrument, there should be no hesitation 

 about omitting it altogether ; with .practice it is quite 

 easy to give a most delicate movement to a slide with 

 the fingers if it is held on a good flat stage by means 

 of clips. If no mechanical stage is fitted, either a square 

 or circular and preferably rotating stage may be selected, 

 according to requirements, and assurance should be 

 made that the stand is suitable for the addition of an 

 adaptable mechanical stage. Most makers provide 

 excellent stages of this description to be added to existing 

 stands, for instance, the stage shown with the Leitz 

 stand at Fig. 16. Another very reliable one with which 

 we are familiar is made by Ross ; it may, if desired, be 

 fitted with a micrometer arrangement for measurements. 

 On the whole, mechanical stages built into the stand 

 are preferable to the adaptable type, which are more 

 liable to wear slightly loose or out of true. A very good 

 compromise, combining the rigidity of the built-in and 

 the convenience of the adaptable, is fitted to the Zeiss 

 and Baker stands shown at Figs. 15 and 17. In these 

 the motion to and from the limb is built in, while the 

 transverse movement is given by means of a bar which 

 can be verv firmlv attached and readilv removed when 



