XIX, 1. R h e i n b e r g : Common Basis of the Theories of Microscopic Vision. 1 1 



6 10 6 



G 10 G 



(3 10 G 



G 10 G 

 G 10 G 



G 16 22 22 22 IG G 



Excepting- near the edges of tlie envelope, each point withiu it has 

 the whole series of intensities superimposed , resulting in a certain 

 definite amount of brig'litness. The consequence is tliat no matter 

 wliat the intensity curve of tlie disc Image of a Single point is, we 

 obtain for a continiious series of points an evenlj^ ilhniiinated area 

 with fading oif edges (fig. 9, RR'). 



The bright rings in lil^e mauner overlap and form an annular 

 surface evenly illuminated throughout its breadth except at the edges, 

 bnt it will be observed that as soon as the centres of the discs are 

 further apart than a disc is from its rings, overlapping of discs and 

 rings takes place , and the latter merely form a fading otf part of 

 the edge of the total area. That is easily seen by comparing the 

 following, taken to represent equidistant points ou discs and rings 

 which are overlapping : 



— 1 GIO G 1 — 



— 1 G 10 G 1 — 



— 1 G 10 (3 1 — 



— 1 GIO G 1 — 



— 1 1 1 1 G IG 22 22 IG G 1 1 1 1 — 



— 1 — G 10 G — 1 — 

 — 1 — G 10 G — 1 — 



— 1 — G 10 G — 1 — 



— 1— 6 10G — 1 — 



— 1 1 7 17 22 22 17 7 1 1 — 



In the first addition the rings are separated by five units of distance 

 from their discs, and form an evenly illuminated ring, in the second 

 addition they are separated by one distance unit , their separate 

 identity is lost, and they are but an edge of the illuminated area. 

 The distance of the rings from their discs is , as we have 

 already seen , dependent on the effective aperture of the lens , and 

 is very small as soon as this exceeds a couple of millimetres ; the 

 distance apart of any two discs , besides being dependent on the 

 amount of Separation of the two points in the luminous source, 



