Vol. IX] WOODWORTH— OPTICS OF THE MICROSCOPE 177 



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O si ti V e 



E dge focus 



egative 



n 



Central focus 



AXIAL 

 ABERRATION 



STIG- 

 MATA 



?Q%\X\ 



Fig. 1. Chart illustrating the appearance under the microscope 

 of the five spherical aberrations. 



