Critical Microscopy. By E. M. Nelson. 



285 



waiting to see some results worthy of [ that theoretically perfect 

 method of microscopical illumination. 



Critical Image.— The image of an object is critical when it is 

 obtained by means of an objective of fine quality which has been 



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Fig. 46. 



placed in correct adjustment for that object by its screw collar, 

 or by the alteration of the tube length, and when the illumination 

 is critical. 



Critical Illumination. — An object is said to be illuminated 

 critically when ic is placed at the apex of a solid axial cone, the 



