216 THE ELEMENTS OF VEGETABLE HISTOLOGY 



Example. 



100 divisions of ocular scale cover 56 of the stage scale. 



1 division of stage scale equals 0.01 millimeter. 

 56 divisions of stage scale equals 0.56 millimeter. 

 100 divisions of ocular scale equals 0.56 millimeter. 

 1 division of ocular scale equals 0.0056 millimeter. 



In standardizing ocular micrometers with high- 

 power objectives it often happens that the end lines of 



FIG. 71. Filar Micrometer. 



(Bausch & Lomb.) 



the ocular micrometer fall between lines of the stage 

 micrometer. This difficulty may be overcome by 

 making slight changes in the tube length until the 

 lines of both micrometers coincide. Micrometer values 

 must be established for each combination of objectives 

 and oculars, and the tube length must be constant 

 for each valuation. Record should be made of the 

 micrometer values and tube lengths with the different 

 combinations. 



