172 



micrometer form a complete apparatus and a 

 lateral adjustment of the scale across the field is 

 given by a screw. 



Fig. 45. 



In either of these forms the ruled lines appear to 

 lie directly on the image of the object, but while 

 we have on the one hand the actual value of the 

 micrometer we have on the other only the image 

 of the object. The valuation 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 micrometer 

 divided into the same spaces as the eyepiece 

 micrometer is necessary.' 



Focus the eye lens on the eyepiece micrometer 

 and the objective on the stage micrometer, being 

 careful to bring 1 the first line of the former coinci- 



