MICROSCOPIC MEASUREMENTS Pal 
to find how many lines of the ocular scale are covered by the 
object. The number of lines multiplied by the equivalent of 
each line will be the size of the object in microns, or micro- 
millimeters. 
MICROMETER EYE-PIECES 
Micrometer eye-pieces (Figs. 23 and 24) may be used in 
making measurements. These eye-pieces with micrometer com- 
Fic. 24.—Micrometer Eye-Piece 
binations are preferred by some workers, but the ocular microm- 
eter will meet the needs of the average worker. 
MECHANICAL STAGES 
Moving objects by hand is tiresome and unsatisfactory, first, 
because of the possibility of losing sight of the object under 
observation, and secondly, because the field cannot be covered 
so systematically as when a mechanical stage is used for moving 
slides. . 
The mechanical stage (Fig. 25) is fastened to the stage by 
ascrew. ‘The slide is held by two clamps. There is a rack and 
