Cloudiness : Note on a Novel Case of Frequency, 287 



u Cloudiness : Note on a Novel Case of Frequency." By Karl 

 Pearson, M.A., F.R.S., University College. London. Re- 

 ceived December 1, — Read December 16, 1897. 



In a memoir on Skew Variation, contributed some time back to 

 the ' Philosophical Transactions,'* I pointed out (p. 364) that we 

 might expect theoretically to occasionally find U _sna P e d distribu- 

 tions of frequency. I was unable at that time to refer to any case 

 actually known to me except Mr. Francis Galton's curve of " con- 

 sumptivity." The data in that case did not seem to me sufficiently 

 definite to base any elaborate calculations upon them. Quite recently, 

 in studying Hugo Meyer's 'Anleitung zur Bearbeitung meteorolo- 

 gischer Beobachtungen fur die Klimaiologie,' Berlin, 1891, I came 

 across, on S. 108, the table for the frequency of various degrees of 

 cloudiness for the decade 1876-85, at Breslau. Although the 

 method used for determining the extent of cloudiness is not entirely 

 satisfactory, and, as Herr Meyer rei narks, the observer must have had 

 some personal bias with regard to the grade 9, still the observations 

 are so numerous, and so markedly (J -shaped, that I thought it well 

 worth investigating how far my theory of skew variation would 

 suffice to describe such a novel form of frequency. 



The observations are as follows : — 



Degrees of Cloudiness at Breslau, 1876— -1885. 



Degree 1 2 3 4 5 6 7 8 9 10 



Frequency.... 751 179 107 69 46 9 21 71 194 117 2089 



The total number of days of observation is 3,653. 



Clearly no cloudiness and absolute cloudiness are both maxima 

 while the mean cloudiness will not be very far removed from mini- 

 mum frequency. 



The following data were obtained for the distribution by Miss 

 Alice Lee, by the methods of the memoir referred to above : — 



Mean = 6'8292 /3 X = 0-6112 



jti 2 = 18*2999 /3 2 = 1*7414 



fi z — —61-2030 6 + 3^—2^2 = 4'3508 

 ^ 4 = 583-1838 



The theoretical curve is thus one of limited range. 



* Series A, vol. 186, 1895. 



