io8 



MAGNIFICATION AND MICROMETRY 



[CH. IV 



and image) must be gi -r- T 2 T = 47. That is, the magnification is 47 

 diameters, or 47 times linear. If the fractional numbers in the above 

 example trouble the student, both may be reduced to the same denom- 

 ination, thus : If the size of the image is found to be 9A mm. this 

 number may be reduced to tenths mm., so it will be of the same 



Image 



Objective 



'^| Object-b 



Object-a 

 Fig. 99. 



Figs, 98-99. Figures showing that the size of object and image very directly 

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

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

 the tube is lengthened. See also fig. 58. 



denomination as the object. In 9 mm. there are 90 tenths, and in f 

 there are 4 tenths, then the whole length of the image is 90 -f- 4 = 94 

 tenths of a millimeter. The object is 2 tenths of a millimeter, then 



