presses against its lower surface, thus offering the 

 minimum of friction, with sufficient resistance to make 

 an easy movement. 



Mechanical Stage. This is a very important 

 form in which the movements are mechanical, in two 

 directions at right angles to each other, motion being 

 transmitted through the milled heads by a rack and 

 pinion or screw. It is a most useful accessory and 

 with it work can be done systematically and rapidly 

 with the assurance that every portion of the field has 

 been covered and with a degree of comfort which must 

 be experienced to be appreciated. For instance, in a 

 bacteriological or urinary specimen, where one is 

 searching the field for certain objects, it is the only 

 reliable means of covering each portion of it. This 

 stage is especially valuable for blood counting and 

 plankton work. While not many years ago it was 

 spurned by many scientists as a toy, it is now generally 

 accepted as an invaluable part of a microscope. In 

 order to be so, however, it must be of the most perfect 

 workmanship, which is difficult to attain on account of 

 the necessarily small parts of which it is composed and 

 the hard usage which it must bear. The movements 

 must be smooth and easy and on reversing the milled 

 heads, must not show any lost motion or dead point. 

 A great deal of attention and ingenuity has been 

 applied in the development of the modern mechanical 



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