252 SIB DAVID BREWSTER ON THE 



After a cloud had passed the polarisation was diminished. 



Mean Time. 

 3 h 15 m R=22£° maximum in plane of zenith and sun. 



R=14£ elsewhere. 

 5 R=26^ maximum in plane of zenith and sun. 



R=24£ in horizon. 



Babinet's neutral point near the sun. 

 7 R = 22J° in zenith and horizon. 



Height. 



7 Arago's neutral point.* 22° 5' 



8 Do. do. 17 48 



9 Do. do. 15 50 



R=:20i 3 in zenith. 

 R = 22J in horizon. 



1841, May 25. 



Mean Time. 

 6 h m Arago's neutral point in horizon, and the hyperbolic neutral line distinct. 



1841, May 27.— Slightly hazy. 



Mean Time. 

 4 h 45"> R = 20i° in zenith. 



R^19^- in horizon. 



Babinet's neutral point not seen. 



1841, May 28. 



Mean Time. 

 ll h m R=15^°. Hazy bands, ill-defined and ragged. 



Observations resumed at St Andrews. 

 1841. June 3. — In the morning, R = 14^~ and 18^. 



Mean Time. 

 6 h m p.m. R=25£° in zenith and horizon. 

 6 27 Arago's neutral point not above horizon. 



6 3<> Do. do. very near the horizon. 



6 43 Do. do. above and close to horizon. 



See Edin. Trans, vol. xxiii. p. 214, for the height of Arago's neutral point. 



1841, June 6.— Barom. 29-9. 



Mean Time. 

 4 h 45 ra p.m. R=14|° through zenith. 



R=23J 45' above S. horizon. 

 R = 22J in S. horizon. 



In and near the horizon, the white bands of the polariscope are bluish on the 

 side of the neutral line from the sun. Maximum polarisation more than 90° 

 from sun, and diminished by clouds coming on. 



Mean Time. Arago.j 



6 h 0» | r 18° 36' 



8 20 \ Sky verv clear. \ 19 28 



8 30 J ( 21 20 



* The height of Arago s neutral point is to be understood as above the antisolar point, and 

 that of Babinet as above the sun. 



t The numbers under Arago and Babinet ai-e the heights of their neutral points above the 

 antisolar point and the sun. 



