ON THE POLARISATION OF THE ATMOSPHERE. 



217 



1842, February 16.- 



Apparent Time. 



-Barom. 3016. 



K=Maximum Polarisation. 

 In Zenith. In Horizon. 



Height of Neutral Point above 

 the Antisolar Point. 



12'' Om A.M. 



2 48 „ 



18 „ 



22 „ 



44 „ 



12 „ 



37 „ 



58 „ 



A China-ink muddy sky. 

 22i 

 A secondary neutral point. 



Neut. Point not risen. 



22i at 25° Alt.. 



Do. 



10° 



12 



17 



17 



18 



do. 



30' 







30 



10 



20 



1842, February 18. — Cold, wind west and rather strong. 12^ 0", I observed 

 a curious effect on the polarised bands in the west, the sun's altitude being about 

 30°. In carrying the bands vertically round, the neutral line, in place of crossing 

 them at a right angle, was the arch of a circle, to which one of the bands was a 

 tangent. The sky was clear, but in a short time a cloud was formed in that 

 place. I had observed the same phenomenon previously. It indicates a state of 

 the air similar to that which produces mirage. 



1842, February 21. — Barom. 29 44. Wind west. The sky-line over both the 

 sea and the land unusually distinct and free from haze. 



Apparent Time. 



Height of Neutral Point above 

 the Antisolar Point. 



3h 45m P.M. 



3 57 „ 



4 31 „ 



4 37 „ 



5 6 „ 



10° 



29' 



12 



39 



17 



40 



18 



35 



19 



49 



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



, „• R=:Maximuin Polarisation. Height of Neutral Point above 



"° In Zenith. In Horizon. the Antisolar Point, 



.5h25«»p.M. ... ... 13° 26' 



5 32 „ ... ... 15 25 



6 21 „ 30 26i- 19 1 



6 55 „ ... ... 18 50 



7 12 „ 304 ... 21 5 



N^.B. — This and April 8th are the only days on which I was able to observe all the 



• three neutral points, and determine their place. (See pp. 225 and 229.) 



1842, April 6. — Barom. 30"05. Considerable haze. 



. _,. Height of Neutral Point above 



Apparent Time. ° .■, . .. , r> ■ ^ 



' ' the Antisolar Point. 



5'' 23m 15° 26' 



R=Maximuin Polarisation. 

 In Zenith. In Horizon. 



, April 



8. 



Apparent Time 



5*" 30™ 



P.M. 



5 



38 





5 



46 





5 



52 





6 



5 





6 



22 





6 



47 





7 



5 





7 



18 





24^ 



27i 

 28f 



m 



Height of Neutral Point above 



the Antisolar Point. 



15° 



26 



19 







19 







19 



5 



21 



25 



20 



55 



20 



30 



19 



55 



20 



15 



