THE MICROSCOPE AND ITS PARTS. 4I 



lines on glass, the spaces between the lines varying 

 from Y^T to TTnjT '"^^ ^^ ^^^^- Micrometers are said 

 to have been ruled with one million lines to the inch, 

 but the human eye using the best and highest-power 

 objectives has never seen them and never will. All 

 micrometers are prepared by a ruling machine made 

 for the purpose. They are of two kinds, the stage- 

 micrometer and the eye-piece micrometer. 



The beginner will not need a micrometer of either 

 kind, but he may desire to know how to use them. 

 Place the stage-micrometer on the stage, turn the micro- 

 scope horizontal, with the reflector referred to above 

 fitted to the eye-piece. With the low-power objective 

 focus the lines that are -^-^ inch apart, and draw them on 

 the paper. Do the same with every objective, draw- 

 ing the j-jij-TT ^'^ch spaces with the -^ or the -^ inch 

 lenses. These drawings will form the scale for 

 measuring the drawings of the magnified objects. 

 Thus, if the magnified object, when drawn, occupies 

 two spaces of your paper scale made from the yot ^^ch 

 micrometer spaces, the object will measure -j^-^, or -^ 

 inch in length; if five spaces of your scale, then it will 

 measure .^f^, or -^^ inch long; if only one-half a space 

 of your scale, then it will measure one-half of y^ of 

 an inch; if one-fourth of your scale space, then its 

 actual length will be ^^-jy inch. 



If the 1 or the -|- inch objective is used in making 

 your scale from the ^^-w i"ch micrometer spaces, then 

 each division on the paper will represent y^^ inch, 

 and if the drawing of the object measures two of these 

 spaces on your scale, the real length of the object will 

 be -j-jf^^ inch, or -^. It is perceived that the stage 

 micrometer cannot be used for measuring objects 



