1186 
for n==1,310 (yellow); further for the same angles the deviation 
which gives the place of the central maximum and finally the place 
of the first diffraction-minimum on both sides of the central 
maximum, assuming at the minimum-deviation a distance between 
central maximum and first minimum of 100’ (a value about equal 
to the one found in the special case to be dealt with further on 
corresponding to an absolnte width of the slit a of 20.24 u.) 
The positions of the maxima and minima for the D-line derived 
from this are as follows 
— += | 
ist min. Ist max. | 
Te i 
i | Ist min. | Ist max. Ist min. 
1st min. 
PN Nee? 23°43’ 
20°13’ 
36°59’ 21°55! 23°44’ 
31 55 re Ee: cle ENE eee a a 5 59 
38 53 950”) 53 35 | 460 RN 
TE en Ee 8 
40 55 022) 80 4“? 30.) 480 0 14 
ae ies ffi) aan to 12 22 
ae? | 53 | 39 | 500 16> 4.) 30 
The peculiar movement of the inside minimum is due to the 
cooperation of the change of the minimum deviation and of the 
angle of diffraction of the first minimum. 
The results show that for angles of incidence between 39° and 
48° the inside minima do not deviate by more than 5’ from the 
smallest value, that the same is true for the outside minima between 
39° and 42°, and finally for the central maximum from 38° to 44°. 
What was found for yellow, also holds mutatis mutandis for the 
other colours. 
By the superposition of these maxima and minima the development 
of colour will be much promoted in a manner, which is impossible 
on the ordinary refraction-theory, and by the presence of the dif- 
fraction minima the resulting colour is completely modified. This is 
particularly true for the first minimum on both sides of the central 
maximum. The theory taken generally shows the possibility of the 
formation of diffraction rings on both sides of the central maximum ; 
but it goes without saying that these circles have a better chance 
of becoming visible on the light-free inside of the halo than on the 
outside which is covered with non-minimal light. 
The resulting colours and the intensity of the light in each direction 
