356 Sir David Brewster on the Polarization 



1842, August 2. — At St. Andrews; Barom. 30 in. 



Apparent time 

 h m 



5 9 



5 27 



6 15 



Ihe bands opposite the sun begin to weaken, and there is 



a second neutral point. 

 Negative bands distinctly seen. 





 26 

 29 

 54 

 13 



32 

 39 



Arago. 



20 36 



25 1! 



23 1 



22 41 



33 40! 



Babinet. 



13 40 



Arago's secondary neutral point distinctly formed. A dark 

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



1842, August 4. — Slight rain in morning; barom. 29*5 in.; 

 wind west. 



R=25|° near horizon. 



Arago's secondary neutral point in horizon. 



R=29^° in clear blue sky. 



5 54 



6 41 



7 6 

 m q I Altitude of Arago's neutral point above , -.r . ( 



| horizon 



I observed a singular 

 Fig. 6. 



]842, August 5. — Rain in forenoon, 

 sky in the west, to the north of 

 the sun and below him. The 

 whole sky, from A A to the ho- 

 rizon 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 singular, these differ- 

 ently coloured spaces were se- 

 parated by an irregular line 



mmm, showing that the whole space m m m HH was a thin sheet 

 of cloud or vapour terminating abruptly at mmm. 



A 



Darker blue. 



A 



m 



in 



m 



B 



Pale blue. 



B 



H 



Whitish. 



H 



5 40 R=17|°, max. polarization at alt. 40°. 

 7 Q1 jR=27i° in zenith plane, and 26^° at 



' Ji ) alt. 40° 



7 25 A cloud approaching the neutral point. 

 7 40 R=28|°, maximum in zenith plane. 



Arago. 



17 10 



16 35 

 19 30 



1842, August 6. — Barom. 29*6 in. ; rain at 5 h p.m. 



7 50 R = 28|° max. in zenith plane, to 24|° in horizon. 



Altitude above horizon of Arago's neu- 



7 56^ 



I tral point 



Clouds around the blue space. 



19 10 



