9 6 



MAGNIFICATION AND MICROMETRY 



\CH. IV. 



image consult Ch. V. Measure the image with dividers and obtain the 

 power exactly as above (§ 147, 148). 



Thus : Suppose two of the ^nj-th mm. spaces were taken as object, and 

 the image is measured by the dividers, and the spread of the dividers is 

 found on the steel rule to be gf millimeters. If now the object is yiyths 

 of a millimeter and the magnified image is gf millimeters, the magnifi- 

 cation (which is the ratio between size of object and image) must be 

 9f -T- yo = 47. That is, the magnification is 47 diameters, or 47 times 

 linear. If the fractional numbers in the above example trouble the stu- 



Image 



Object 

 Fig. 93. 



Objective 



Objecl-b 

 «| Object-a 



Fig. 91. 



Figs. 93-94. Figures showing that the size of object and image vary directly as 

 their distance from the center of the lens. In Fig. 94 one can also see why it is 

 necessary to focus down, i. e„ bring ihe object and objective nearer together when 

 the tube is lengthened. 



