objectives for color correction ; on the contrary we 

 particularly recommend such tests as will tend to 

 more critical judgment of the optical properties of 

 the instrument and work in general. To aid those 

 who have not had sufficiently long experience to reach 

 correct conclusions, methods for judging color correc- 

 tion are given which should be applied to doubtful pro- 

 ducts ; but the experiments should be repeated quite 

 often before reaching a conclusion. 



To judge under-correction by central light, focus 

 upon a coarse object and it will be found to have a 

 distinctly bluish tinge. If not pronounced, by slightly 

 increasing the distance between objective and object, 

 the latter will show a blue color and by decreasing 

 the distance an orange color. 



To judge over-correction, after focusing on the 

 object, this will show an orange color, or by increas- 

 ing the distance between objective and object the orange 

 will appear, and by decreasing the distance, the blue. 



To judge color correction by oblique light: Under- 

 correction will show when the mirror is swung to the 

 left and the object is fringed with orange on the left 

 and bluish on the right. 



Over-correction is apparent when the object is 

 fringed with blue on the left and orange on the right. 



Another method is that recommended by Naegeli and 

 Schwendener in their work an the microscope. The 



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