164 Sir David Brewster on the Polarization 



1842, April 8. 



R= maximum polarization. Height of neutral point 

 Apparent time- In zenith. In horizon. above the sun. 



h m o o o i 



6 24* 18* 17 15 



6 25 . . . . 18 20 



6 45 27| .. 19 11 



7 7 28f . .. 21 5 

 7 20 . . . . 19 31 



1842, April 13.— Barom. 30*12. in. Fine day. 



5 51 . . . . 18 50 



6 23 29 22* 18 



6 58 29* . . 18 40 



7 12 .. .. 17 35 

 7 21 30* . . 17 57 



At 7 h 32 m the maximum polarization or rotation was 32^°, 

 the greatest ever observed. (See p. 174.) 



1842, May 15.— A haze. 



6 34 15 15 18 10 



6 48 .. .. 19 55 



7 28 20* . . 17 44 



8 29 23* .. 18 1 



1842, November 14. — Barom. 29*6 in. Fine, frosty and clear 

 morning. 



8 58 a.m. 25* 19* 14 7 



1842, November 21. — Barom. 29*77 in. Frosty morning. 

 Thermometer 31°. 



9 4 a.m. . . . . 18 36 



1842, December 28.— Barom. 29-56 in. 



11 40 a.m. 29 .. 13 41 



12 3 p.m. 27 18* 13 37 

 1 4 „ .. .. 25 25! 



1 23 „ .. .. 27 30! 



2 31 „ 14* .. 27 48! 



These remarkable results were doubtless owing to the causes 

 which produced the following phenomenon : — At l h 4 m , when 

 the neutral point started away from the sun, a white halo of 45° 

 appeared round the sun and continued till 2 h 31 m . It was 

 slightly brown on its inner rim. At l h 23 m the altitude of the 

 halo was 32° 10', and the sun's altitude 8° 30', so that the 

 radius of its outer rim was 23° 40'. 



When the vertical bands of the polariscope passed over the 

 apex of the halo their intensity was increased, and when they 

 passed over the halo in a direction parallel to its horizontal dia- 

 meter their intensity was diminished. As the crystals of ice, 



