506 J. RHEINBERG, DARK-GROUND ILLUMINATION. 



never carried beyond the determination of the forms of star 

 images. 



Summing up, it will be seen that whilst the controversy has 

 not afforded any evidence whatsoever against the famous Abbe 

 Theory of Microscopic Vision, it has brought out, firstly, that we 

 can have dark-groand effects without refraction ; secondly, that 

 under practical conditions refraction certainly plays its part ; and 

 lastly, it has afforded data which throw new light upon the 

 extent of the part which refraction plays under different con- 

 ditions of aperture of the objective and illuminator. 



Journ. Qvekett Microscopical Club, ^cr. 2, Vol. XI., No. 71, November 1912. 



