Replace the stage micrometer by the object to be 

 measured and bring one edge of the object coincident 

 with the first line of the eyepiece micrometer, being care- 

 ful to leave all the conditions unchanged. Note how 

 many divisions are required to cover the object and 

 divide by the figure first obtained with the stage micro- 

 meter. 



Thus if an object 

 covers forty spaces 

 of the eyepiece mi- 

 crometer its real size 

 will be (40 8) x 

 o.oi mm. = 0.05 

 mm. 



If measurements 

 are made under ex- 

 actly the same condi- 

 tions of tube length, 

 with same objectives, 

 it will be unneces- 

 sary to repeat the 



operation with eyepiece and stage micrometer, as the 

 ratio remains constant and maybe marked on a card 

 for reference. 



The most efficient apparatus, however, for obtaining 

 accurate results is theyf/^r or screw micrometer, Fig. 59. 

 This consists of a metal case to the upper surface of 



Measuring an object with the eyepiece 

 micrometer. 



180 



