1896.] MICROSCOPICAL JOURlSrAL. 17 



One thing the diffraction theory did, it settled forever 

 striving after useless magnifying power in objectives; 

 such as 1-40 and 1-50 of very small aperture, and led 

 opticans to construct lower powers 1-8 and 1-12, of large 

 aperture, from which more could be gained. 



That the true resolution of an object is affected by a 

 wide cone instead of a narow one is now beyond question, 

 consequently the laws of optics are Justin the same place 

 as when demonstrated by the old writers. But having 

 this extreme oblique illumination and resolving of the 

 strisB is a true image formed, such as can be obtained 

 with a dioptric or wide cone ? It will be found both by 

 observation and measurement that the diffraction image 

 is utterly false. The striations are seen as considerably 

 finer than the true structure, also markings are shown of 

 an elongated form. The diffraction spectra can only be 

 shown by very narrow pencils of light. And the nar- 

 rower the pencil the sharper the so-called image. But 

 to get a true image we must employ a large cone. We 

 saw with the pinhole that a ray formed an image; but 

 that image had no focus. When we put a lens in its 

 place there is a definite focus, because, at one point only, 

 a diverging cone of rays from. a point in the object is 

 converged into another cone, whose apex is as small and 

 sharp an image of the point as the aperture and correc- 

 tion permit. 



Any such image, formed by rays first diverging from 

 a point, and then converged by the corrected refraction 

 of a lens to the image point, is a dioptric image, and 

 every real microscope image is dioptric. What we want 

 is an objective that will give a true dioptric image coupled 

 with a good condenser having an aplanatic cone. With 

 these the narrow cone theory is intolerable. Given ob- 

 jectives and condensers good enough, the best results in 

 definition and resolution of fine structure have been with 

 wide cones. 



