The Mechanical Stage, while an absolute neces- 

 sity in petrographical and other work where a systematic 

 search, as for bacilli or in blood counting, over the 

 entire surface of object is required, will also be found 

 a most useful accessory. The obstacle of considerable 

 cost which formerly prevailed is now removed and 

 good mechanical stages may be obtained at a very 

 reasonable cost. They are supplied in two forms : 



Fixed mechanical stage, in which the mechanical 

 movement is an integral part of the stage. 



Attachable mechanical stage, which can be attached 

 to the Continental stands having plain stages. This 

 has advantages, since it may be removed, leaving the 

 stage plate free, but it cannot be revolved. Either 

 form involves the most delicate work and while the 

 parts are necessarily small should be built with a view 

 to strength and durability. They should work with the 

 utmost precision and smoothness and with absolutely no 

 lost motion. 



Revolving Stage. While this is also a great 

 convenience in all work, it is a necessity in some 

 directions, and when provided with centering screws 

 may be used to some extent as a mechanical stage with 

 only a limited movement, however. It should work 

 freely with the rolling motion of one finger, without 

 any side play and without throwing the object out of 

 the plane of focus during revolution. 



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