have on the one hand the actual value of the micro- 

 meter we have on the other only the image of the 

 object. The value of the eyepiece micrometer in the 

 value of the stage micrometer must be first determined. 

 While the optician can do this, it should be done by 

 the manipulator on account of the varying conditions 

 of tube length, power of objective, etc. A stage micro- 

 meter ruled in the same values as the eyepiece micro- 

 meter is necessary. 



Focus the eye lens 

 on the eyepiece micro- 

 meter and the objec- 

 tive on the stage mi- 

 crometer, being care- 

 ful to bring the first 

 line of the former 

 coincident with a line 

 of the latter, using 

 care to see that they 

 are parallel. As the 

 lines of the stage mi- 

 crometer will appear 

 to hare a certain 



amount of thickness, make the first line of the eye- 

 piece micrometer correspond with one edge of a line on 

 the other. Now read off how many of the lines are 

 contained in one space of the stage micrometer and note 

 this. We will assume that there are eight divisions. 



The eyepiece micrometer compared with the 

 stage micrometer. 



I 79 



