296 



ANGULAR AXD NUMERICAL APERTURE 



[Ch. IX 



mersion; and u, is the sine of half the angle of the light entering the 

 microscope objective, no matter what medium is between the object 

 and objective. 



As there are three factors in this formula, if one knows any two of 

 them the third is readily found: 



§ 469. Table of a Group of Objectives with their Numerical Aperture with Method of 

 Obtaining It. For a Table of Natural sines, see third page of cover. 



