of the Atmosphere. 351 



1842, March 4. — Cloudy and sunshine. 



Apparent time. Arago. 



h m 



1 18 R=25|° in zenith, and 22|°at 30° alt. W. horizon. 



1 48 One plate of glass at 60° incidence compensates the po- 

 larization on the sea -horizon opposite the sun. 

 3 53 , 



3 58 .. .. .. . . 11 13 



5 23 . . . . . . . . 12 22 



5 26 17 55 



Babinet. 



5 38 R=27^° in zenith, and 221° in horizon. 17 22 



1842, March 7. — ll h 30 m R = 28i° in zenith, to 18J in 

 horizon j but at l h 30 m , after showers of hail and rain, 11 = 22^° 

 in zenith. 



1842, March 10. — Sky clear, and wind in west. 



11 R = 27i° in zenith. 



11 15 Neutral point seen below sun. 



3 14 R=28° in zenith, 24^° in horizon. 



4 Arago's neutral point not risen. 



4 10 The + bands scarcely seen in horizon. 

 4 13 R=28° in zenith. 



Arago. 



4 15 . . .... . . 12 55 



4 20 .. .. .. .. 13 56 



4 ny I The secondary neutral point just touch-) ,. r 4 

 ' j ing the sea horizon . . j 



1842, March 13.-— 12 h 36 m R = 26J° in zenith. Sky clear. 



4 27 The breach in the + bands not completed. 12 15 

 4 39 But at 4»39 m the neutral point is formed. 12 6 



Both on the 10th and 13th Arago's neutral point is above the 

 horizon, though marked by the cause which produces the secon- 

 dary neutral point. Over a space of 3^° above the sea-horizon, 

 the + bands almost wholly disappear before the — ones are 

 perceptible, and the neutral point is distinct on the sea-horizon. 



1842, March 16. — Barom. 22'96 in., the sun occasionally 

 shining through a thickish haze in a sky without blue. Wind 

 slight in south-west. 



10 45 Polarization the same as on March 2 ; Babinet's neutral 

 point 30° above the sun, or more than 60° above the 

 horizon ! 



1842, March 17.— Barom. 29'77 in. Much rain last night. 

 Wind west ; white clouds flying. 



] 20 R=26|° in zenith plane, and soon after 24£°. 

 10 50 R=20|° in zenith plane, and in a clear sky over which 

 clouds have passed. 



