270 SIR DAVID BREWSTER ON THE 



1842, May 9.— Barom. 29-83. 



R = 22|° in zenith plane. 



Bands all positive. 



Positive bands still in horizon. 



pan 



>nt Time 



5h 



42m 



6 



7 



6 



18 



6 



39 



7 



28 



6 



45 



7 



30 



Arago. 



19° 



15' 



22 



47' 



23 



21 



Babinet. 



15° 



0' 



16 



5 



R=19£° in zenith plane. 



1842, May 15, 16, 17.— See "Edinburgh Transactions," vol. xxiii. pp. 218,230, 

 231. 



1842, July 16.— At Lacock Abbey, Wiltshire. 



R=23° in a singularly fine day, this low polarisation indi- 

 cating nebulosity, which collected and produced rain. 



1842, August 2.— At St Andrews; Barom. 300. 



Apparent Time. 



5 h 9 m R=20£° in zenith, and I4£° in horizon. 



_ „,_ f The bands opposite the sun begin to weaken, and 



\ there is a second neutral point. 

 6 15 Negative bands distinctly seen. Arago. 



6 20° 36' 



6 26 25 1 ! 



7 29 23 1 

 7 54 22 41 

 9 13 33 40! 



Babinet. 

 6 32 13° 40' 



( Arago's secondary neutral point distinctly formed. A dark 

 \ band along the horizon, below Arago's neutral point. 



6 39 



1842, August 4. — Slight rain in morning ; Barom. 29-5 ; wind west. 



Apparent Time. 



5 h 54 m R=25|° near horizon. 



6 41 Arago's secondary neutral point in horizon. 



7 6 R = 29i-° in clear 'blue sky. 

 7 9 Altitude of Arago's neutral point above horizon, 15° 40 



1842, August 5. — Rain in forenoon. I observed a singular sky in the west, 



to the north of the sun and below him. The whole sky, 

 from A A to the horizon H H, was clear, but the part 

 A A was darker than B B, and of a deep China-ink 

 blue, while B B was much paler. But, what was sin- 

 gular, these differently coloured spaces were separated 

 by an irregular line m m m, showing that the whole 

 Flg ' 6 ' space m mm H H was a thin sheet of cloud or 



vapour, terminating abruptly at mmm. 



Apparent Time. 



5 h 40 m R=17|°, maximum polarisation at alt. 40°. Arago. 



7 21 R=27|° in zenith plane, and 26|° at alt. 40°. 17° 10' 



7 25 A cloud approaching the neutral point. 16 35 



7 40 R=28J°, maximum in zenith plane. 19 30 



A 



Darker Blue. 



A 



m 



B 



m 



Pale Blue. 



m 



B 



H 



Whitish. 



H 



