256 SIR DAVID BREWSTER ON THE 

 1841, July 24. 



Mean Time. Arago. 



6 h 40™ R=14i°; cloudy sky. 25° 55' 



1841, July 28.— Barom. 29'37. A clear blue sky ; cloudy. 



Mean Time. Arago. 



7 h 10 m ") f 18° 12' 



7 40 / R _ 961 o 281C ) 18 43 



7 57 f tt — «>l ^ ^2 < 17 53 



I 



8 10 j ^ 18 5 



1841, July 31. — Cloudy. Neutral point covered with minute cirri. 



Mean Time. Arago. 



8 h m 16° 45' 



8 14 17 25 



1841, August 6. — After two days of rain. 



Mean Time. Arago. 



8 h 5 ra p.m. B=29}°. A cloud had passed. 16° 28' 



1841, August 8. — Morning rainy; splendid evening. 



Mean Time. Arago. 



6^ 50"> R=29|° 16° 17' 



7 5 R=28i 18 20 



7 35 Clouds came on. 17 53 



1841, August 10. — After rain. 



Mean Time. Arago. 



7 h 45^ 18° 15' 



1841, August 17.— Clear and windy. 



Mean Time. 

 9 h m a.m. R = 21J° in zenith, and 15|° near horizon. 



The blue of the sky, though very clear, was whitish, which always reduces 

 the polarisation. Same day at Perth. 



Mean Time. Arago. 



7 h 15 ra R=24i° in zenith, and 20^° in horizon. 20° 38' 



7 30 19 24 



During the whole day the blue sky became whiter and whiter, and the polari- 

 sation fell below 14|° out of the scale of the Polarimeter. Small black clouds 

 appeared upon the white sky. 



The observations, from the 6th to the 17th August, were made at the Bridge of 

 Earn. 



1841, August 31, September 6th and 12th. See " Edinburgh Transactions," 

 vol. xxiii. p. 214. 



1841, September 6. — See " Edinburgh Transactions," vol. xxiii. pp. 215, 223. 

 September 12. „ „ „ pp. 215, 223. 



