of the Atmosphere. 127 



1844, February 21. — Barom. 29*28 in. Snow partially cover- 

 ing the ground. 



R= maximum polarization. Height of neutral point 



Apparent time. In zenith. In horizon. above the antisolar point, 



h m o o o i 



3 30 a.m. 27 . . 13 3 



4 40 „ 28^ . . 12 35 

 4 13 ., 28f .. 17 34 



4 40 „ .. .. 19 24 



1844, June 10.— Barom. 29'70 in. 



7 36 a.m. . . . . 21 20 



7 44 „ . . . . 21 20 



8 11 „ 24f 22^ 21 35 

 8 52 „ 27\ 23i 21 50 



1844, June 13. — Barom. 29*4 in. Windy; wind south-west. 



7 a.m. Neutral point in horizon. 11 10 



7 12 „ 24± 20i 13 2 



In the following observations the altitude of the sun was not 

 estimated. The numbers in the fourth column are the altitudes 

 of the neutral point above the horizon. 



1845, April 15. 



5 48 a.m. 26± 22| 7 25 



6 48 „ 27i .241 18 55 



In the normal state of the atmosphere, as represented in the 

 Map, Plate II.*, namely when the sun is in the horizon, Arago's 

 neutral point is about 18^° above the horizon or above the anti- 

 solar point; but when the sun is 11° or 12° above the horizon, 

 and the antisolar point as much below it, the neutral point is in 

 the horizon, and consequently only 11° or 12° above the antisolar 

 pointt- 



As the sun descends to the horizon, and the antisolar point 

 rises, the distance of the neutral point from the latter gradually 

 increases; and when the sun reaches the horizon the neutral 

 point is 18J° above it, and therefore 18J° distant from the anti- 

 solar point. 



After the sun has set, the distance of the neutral point from 

 the antisolar point increases; that is, it rises faster than the sun 

 descends, and its maximum distance, when the twilight is very 

 faint, is about 25°. 



When the sun is advancing to the meridian, and the light of 

 the sky is increasing, the distance of the neutral point from the 

 antisolar point diminishes, as shown in the morning observations 

 on the 14th, 20th, and 21st of November, 1842. 



* This Plate will be given with our next Number, 

 t In abnormal circumstances sometimes only 7°, 8°, 9°, or 10°, as in 

 1842, February 15 and 16. 



