ON THE POLAKISATION OF THE ATMOSPHERE. 



225 



2^ 20"". — The neutral point was 75° above the horizon, or about 54° above 

 the sun. The polarisation was negative from the neutral point to the horizon 

 beneath the sun, and positive to the horizon opposite to the sun. 



1842, March 16. — Barom. 29-96. The sun occasionally shining through a 

 thickish haze in a China-ink sky without any blue ; the wind in the south-west, 

 and slight. 



IQh 45m_ — Sun's altitude about 30^°; the polarisation below the sun was 

 negative down to the horizon ; the neutral point was 30° above the sun, or more 

 than 60° high ! 



1842, April 5.— Barom. 30 07. Splendid sky. 



Apparent Time. 



R=:Maximum Polarisation. 

 In Zenith. In Horizon. 



Height of Neutral Point ahove 

 the Antisolar Point. 



6'' 23°! 



6 58 



7 7 



30" 

 301 



261° 



19° 17' 

 18 46 

 15 45 



The polarisation was unusually great, equivalent to a rotation of the plane of 

 polarisation of about 29° ; it became stronger as it grew darker. 



N.B. — This day and April 8th were the only days on which I was able to 

 observe the three neutral points, and determine their place. (See pp. 217 and 229.) 



1842, 



April 



8. 





Apparent Time 





6^ 



Qm 





6 



25 





6 



45 





7 



7 





7 



20 



R=:Maximum 

 In Zenith. 



Polarisation. 

 In Horizon. 



24J° 



181° 



27i 



28f 



... 



Height of Neutral Point above 

 the Antisolar Point. 



17° 15' 



18 20 



19 11 

 21 5 

 19 31 



1842, April 13.— Barom. 30-12. Fine day. 



. . nr R=:Maximum Polarisation. Height of Neutral Point above 



5h 51m 



in /Cjeniio. 



in Horizon. 



ine Antisoiar r 



18° 50 



6 23 



29° 



221° 



18 



6 58 



29i 



... 



18 40 



7 12 



... 



... 



17 35 



7 21 



30^ 



... 



17 57 



At 7^ 32™, the maximum polarisation or rotation was 32|°, the greatest ever 

 observed. (See p. 235.) 



1842, May 15. — A haze. 



Apparent Time. 



Qh 34m 



15° 



6 48 



... 



7 28 



20^ 



8 29 



231 



R^Maximum Polarisation. 

 In Zenith. In Horizon. 



15° 



Height of Neutral Point above 

 the Antisolar Point. 



18° 10' 

 19 55 



17 44 



18 1 



