16 Modern Microscopy 



were agreed upon between them, so that a person noting a 

 special point with his microscope could send the specimen, 

 with the readings marked upon it, to a brother worker, and 

 he, having the same kind of finder on his stage, would at 

 once be able to find the desired spot. 



The following method would be suitable for the average 

 size of stage : A piece of metal the same size as an ordinary 

 glass slip (3x1 inches) should be adopted as a tool, and 

 | inch from one end and % inch from the edge a minute 

 spot should be made with a small drill. The metal slide 

 should be placed on the stage with the spot towards the 

 front, and the f-inch space to the right of the centre of 

 the stage. The drilled spot should then be placed central 

 in the field of a 1-inch objective, and the outer margin of 

 the square of divisions marked off from the right-hand end 

 of the metal slide. 



The Wright's finder is obviously unsuitable for any other 

 than a stage whose upper surface does not travel. 



In selecting a stage for a microscope our choice would 

 therefore be as follows : 



For a first-class microscope: Mechanical movements; 

 concentric rotation ; screws to make the rotation quite 

 true with any objective ; sliding-bar to top plate and 

 stop-pin for object to go against ; divisions to plates of 

 stage reading to parts of millimetre or inch ; rackwork 

 rotation to stage ; and (optional) divisions to periphery of 

 stage. 



For a second-class microscope : Mechanical movements ; 

 sliding-bar to top plate ; non- concentric rotation. 



For a third-class microscope : Plain stage, with springs 

 to hold object in position ; if provided with sliding-bar or 

 plate as object-carrier, so much the better. 



