ON THE POLARISATION OF THE ATMOSPHERE. 229 



1842, Feb. 16.— Barom. 30-16. 



Apparent Time. 



12*" 0™. Sun's altitude about 21° 13' ; a China-ink muddy sky. There is clearly a 

 neutral space below the sun, and a little above the horizon. The bands 

 on the sun and below him are negative ; but as the negative polarisation 

 becomes very weak, it must pass into a neutral point. 



1842, Feb. 18. — Cold, wind west, and rather stormy. 



Apparent Time. 



12'» 0™. The neutral point below the sun was distinctly seen, the polarised bands being 

 negative over and below the sun, and below the neutral point positive 

 down to the hoi'izon. The sun's altitude was about 22°, and the distance 

 of the neutral point from the sun about 1 5°. 



1842, Feb. 21. — Barom. 20-44. Fine dry day; wind west. 



Apparent Time. Distance of Neutral Point from Sun. 



12'' 39m. Neutral point 61° above the horizon, 15° 0' 



The positive polarisation between the neutral point and the horizon was 

 compensated by the refraction of one plate of glass, at 20° of incidence. 

 The neutral line was convex towards the sun in the west horizon. 



1842, March 10. — Sky clear in zenith ; wind west. 



Apparent Time. 



ll** 15™. The neutral point distinctly seen below the sun. 



1842, April 3. — Barom. 29-8. Fine clear sky ; cold ; hail in the afternoon. 



Apparent Time. 

 jjh 45m Neutral point below the sun very distinctly seen, the sun's altitude being 

 about 39J°, and the height of the neutral point 26|^°. The distance of 

 the neutral point from the sun was 13°. The bands over the sun down 

 to the neutral point were negative, and those below it down to the 

 horizon positive. 



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



Apparent Time. Distance of Neutral Point from Sun. 

 12h 27™. Neutral point seen distinctly below the sun. 



12 27 15° 25' 



12 63 14 40 



12 56 15 45 



4 13 15 35 



4 33 15 22 



N.B. — All the three neutral points were observed, and their places ascertained 

 this day, and also on April 8. (See pages 217 and 225.) 



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



Apparent Time. Distance of Neutral Point from Sun. 



8** 51"°. Neutral point distinctly seen below the sun. 

 11 6 , 12° C 



1842, April 8. 



Apparent Time. 



£11 7m, The neutral point below the sun beautifully 



seen. Estimated distance from the sun, 16° 0' 



