MA GNIFICA TION AND MICROME TRY [ CH. 



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

 must have been a magnification of 94-7-2=47 diameters in order to 

 produce an image 94 tenths of a millimeter long. 



Image 



Object- 



FIG. 109 Fig. no 



Fig. 109-110. Figures showing that the size of object and image rarv 

 directly as their distance from the center of the lens. In Fig. no one can also 

 see why it is necessary to focus down, i. e. bring the object and objectives nearer 

 together ivhen the tube is lengthened. See also Fig. 66. 



Put the 25 mm. (i in., C, or X 12) ocular in place of one of 37 

 mm. focus, and then put the camera lucida in position. . Measure 

 the size of the image with dividers and a rule as before. The power 

 will be considerably greater than when the low ocular was used. 

 This is because the virtual image (Fig. 26, B 3 A 3 ) seen with the 



