JOUKNAL 



OF THE 



EOYAL MICROSCOPICAL SOCIETY, 



OCTOBER, 1905. 



TRANSACTIONS OF THE SOCIETY. 



VI. — Theories of Microscopical Vision. 

 (Second Paper.) 



By A. E. Conkady, F.R.A.S., F.R.M.S. 



{Bead June 21«*, 1905.) 



In a former paper* I endeavoured to show that the explanation of 

 microscopical images must always be sought on the basis of 

 Professor Abbe's theory ; in other words, that the detail is brought 

 out by the light diffracted by the object. I further showed how 

 the formation of the image of a simple plane grating could be 

 fully accounted for on the basis of Abbe's theory, and that the 

 objections which have at different times been raised against that 

 theory are unsound. 



In establishing these results I introduced two essentially new 

 propositions, the first referring to certain interesting differences of 

 phase between different spectra from any one grating, the second 

 serving to explain how the want of definite focus in an elementary 

 diffraction-image is replaced by the much desired well defined 

 focus under the usual working conditions. 



I now proceed to the consideration of more complicated struc- 

 tures — dot and cross-lined patterns — on the same basis. 



It will be remembered that it is with such patterns that the 

 most startling false images are secured in the experiments with the 

 "Diffraction- plate"; it will therefore be extremely interesting to 

 study the images obtainable with such gratings under "normal 

 working conditions," i. e. when the simple circular form of the 

 aperture of the object-glass is not interfered with. 



* J.R.M.S., 1904, p. 610-633. 

 Oct. 18th, 1905 2 o 



