Mr. W. Brennand. 



[Dec. 11, 



Table B. 

 Chemioal Action of Sun and Sky. 



N.B. For sun altitudes 50 to 90, the figures are not the result of direct obser- 

 vations ; for sun altitudes 1 to 10, the figures are less certain by reason of thin 

 haze often present. 



on which stands a style parallel to the tube, by means of which this 

 particular tube can be brought in a line with the sun. By another 

 motion the plane of the tubes can be adjusted to the plane of symmetry 

 (or elsewhere) . 



[A vertical plane through the stm at any time divides the visible 

 sky into two exactly similar portions. I call this the plane of 

 symmetry.] 



19. The observations (Table C) were taken 23rd December, 1864, 

 at Dacca (among other similar observations taken in the same cold 



