Meteorology. — ''On, the (/i/nict/'on of llir I'ujht in the foniiatloti of 

 halos. II. A retiearch o f the colon ys obserred in halo- phenomena''. 

 Bj' Dr. S. W. VissEK. (Coiiumuiicated by Dr. J. P. van dek 

 Stok). 



(Communicated in llie meeling of June 21), 1918). 



In the first paper on the difïVactioii of (lie liglit in the formation 

 of halos') a survey of colours obserxed has been given on pag. 1175 

 taken from "Thunderstorms, optical phenomena etc. in Holland". 



Prof Dr. E. van Everdingen however informed me, that these 

 records are altogether insufficient because oidy a small nund)er of 

 colour observations are dealt with in "Thunderstorms". On his 

 suggestion I have studied a number of' records sent in to the 

 "Koninklijk Nederlandsch Meteorologisch Instituut". In the first place 

 I hope to have set right a neglect against the sincere voluntary 

 observers of the Institute; in the second place this research gave 

 valuable materials for the answer to the question how far and in 

 what manner the diffraction works in the formation of halos. 



In this paper a survey of the research is given ; the results will 

 be discussed and it will appear, that indeed the diffi-action has an 

 important influence on the refraction of light in ice crystals. 



I started with all the colour records in the years 1913, '14 and '15. 

 'i'hen the research was extended to the years 1911, '12 and '13. 

 In the first part 1 soon found, that great prudence was necessary. 

 As an example I take the observations of" "lainbow-colours". In 

 the three years 1913 — '15 I find "rainbow-colours" 12 times recorded 

 by 9 observers. There are however 7 who have never sent in 

 another record during all this time. They were evidently led by 

 suggestion and fancy more than by observation power. The personal 

 character also comes to the front. Therefore it was resolved to niake 

 a very careful selection and only to use records of those observers 

 known to the Institute as wholly reliable. In this manner the notes 

 are studied of eleven observers, who are mentioned in this paper 

 with the numbers I tot XI. 



1) These Proceedings Vol. XIX. 



