123 



Some colours and groups occur relatively often. 



yellow; yellow, white 25 times; 6 observers 



red, yellow; red, yellow, white 16 „ 6 „ 



red, green; red, blue; red, violet 64 „ 8 „ 



red, yellow, green; red, yellow, blue; red, yellow, violet 22 „ 7 „ 



red, green, blue 6 „ 2 „ 



Spectrum colours 5 » 3 „ 



Green, blue and violet, to escape from personal inlluences, are 

 again added. 



The yellow takes a peculiar place. Yellow circles seem to occur. 

 It is clear, that the yellow is often missing between the red and 

 the green, but on the other hand it is often met with. 



As regards the rainbow colours; 5 observations of 3 observers 

 remain in six years. 



Separate mention deserve the estimations of breadth by HKi\ii\JESat 

 Arnheim in the ordinary circle and the tangential arc. 



1911 Dec. 29 red |° yellow i° blue J° 



1912 Feb. 18 



March 3 ' -l° ^° i° 



4 >) 4 '> 4 



May 10 



March 8 ,, i° ,, ^° especially at the top also blue. 



1912 Jan. 6 ) . , ,o ,o i , lo 

 .,Q,Q , , , ^'^'-l 4 ' gi-een i° blue |° 



1913 June 14 ] 



1911 Dec. 3 red i° yellow 1° green i° blue F. 



The fact that the breadth sti-ongly varies also appears from the 

 detailed tables on the circumzenithic arc by Besson^): 17 liuics on 

 91 arcs Besson measured the colours. The distance from red to violet 

 varied from Ji° to 3° (H°: 3 times; 2°: 6 times; 2i° twice; 3°: 

 3 times). Three times blue and violet are wanting; among these is 

 one arc, with which the breadth of the inside red to the green is 

 5°. Besson notes: "tres large, tres brillant". 



These variations of breadth are very important for the theory of 

 ditlfraction. 



Summing up I find as the results of the research after eliminating 

 the individual influences: 



1. the pretty large wealth of colours, 



2. the variation of colours, 



3. the variation of breadth. 



1) Sur la Theorie des Halo's. Paris 1909. p. 62. 



