POLARISATION OF THE ATMOSPHERE. 251 



White clouds ; cumuli in motion. 



Mean Time. 

 12 h m R= 27|° in plane of zenith and sun. 

 R = 20 ; ?r near horizon. 

 R = 25|' at intermediate points. 

 1 20 R = 26^ in plane of zenith and sun. 

 R = 21|- near E. horizon. 



Near the large white cumuli R diminishes. 



R= 30|° in plane of zenith and sun. 



R = 25l in horizon. 



R = 27^ in plane of zenith and sun. 



11 = 24^ in horizon. 



R = 30|- in plane of zenith and sun. 



R = 28Jr in horizon. 



R=30-| in plane of zenith and sun. 



R = 29i in horizon. 



Jean Time 

 4h 30m 



6 







7 



10 



7 



35 



7 



45 



R = 28i in plane of zenith and sun. 

 R = 28^- in horizon. 



See Edin. Trans, vol. xxiii. pp. 213-223, for the places of the neutral points on 

 this day. 



1841, May 1-1.— The sky in the forenoon has very little blue in it, being in its 

 colour a French grey. R less than 14i°. 



Mean Time. 

 3 h 30"> R = 141°, and 



R= 18| in a bluer part of the sky. 



According as the thin white haze which masked the blue colour of the sky 

 was removed or returned, the place of the neutral points constantly varied in 

 their position. 



In the evening the sky became clear, and R became 24^° and 26^°. 



1841, May -16.— See " Edinburgh Transactions," vol. xxiii. p. 223. 



1841, May 16. — Barom. 294. Windy. Considerably above the horizon R 

 varied from 17g° to 14^°, as the blue sky was more or less distant from the white 

 moving clouds. 



At 7 h , when the blue was purer, R = 22^° at 45° of altitude in the S. 



At 7 h 4^ m R = 241° at 20° altitude in the N. 



1841, May 17.— Barom. 295. 



Mean Time. 

 l h 20 m R = 17-o-°, the maximum polarisation at 99° from sun in the plane of zenith 



and sun. 

 2 R= 17 J° and 15J C at lower altitudes. 



The following observations, from May 24 to June 3, were made in Edin- 

 burgh : — 



1841, May 24. 



Mean Time. 



ll h 10 m R=17i° maximum in plane of zenith and sun. 

 R=T1£ in horizon. 

 VOL. XXIV. PART II. 3 Z 



