18fi6.] 197 [Chase. 



opposite polarizations and the position of the neutral points with per- 

 fect ease, even at midday. 



6. In our climate it is by no means unusual to have days on which 

 all the three neutral points can be observed, and their places deter- 

 mined. During the whole period of Brewster's observations at St. 

 Andrew's he found but two such days, April 5th and 8th, 1842 

 (loc. cit. pp. 124, 163). 



7. Quasi neutral lines, dividing bands of opposite polarization, can 

 be found in nearly all parts of the sky by rotating the polariscope 

 45° from the line of maximum positive or negative polarization. 

 But a slight additional rotation will show that the neutralization is 

 only apparent. 



8. The position of a true neutral point can be determined by 

 sweeping its neighborhood alternately with the vertical and with the 

 horizontal bands and marking the intersection of the lines of vanish- 

 ing polarization. 



9. In consequence of the arrangement of the lines of equal polari- 

 zation, when the sky is swept with a polariscope for a few degrees on 

 each side of a neutral point, the line which separates the oppositely 

 polarized bands forms curves with a convexity determined by the 

 position of the sun or the anti-solar point.* 



10. Some of my observations have indicated an apparent correla- 

 tion between these curves and the magnetic dip and terrestrial lati- 

 tude. I have not been able to satisfy myself whether this correspon- 

 dence was merely accidental, or whether it indicated another point 

 of analogy between the laws of light and magnetism. 



11. The varying effects of haze or cloud, appear, on the whole, 

 to confirm Brewster's theory that the neutral point is produced " by 

 the opposite action of light polarized by reflection and refraction." 

 (See pp. 123, 169, 176, 178, 180.) 



12. In one instance, soon after sunset, the reflection from scattered 

 clouds in the neighborhood of the anti-solar point was such as to 

 totally eclipse Arago's neutral point, the polarization being positive 

 over the entire arch, from Babinet's neutral point to the eastern 

 horizon. 



The report of the Judges of the annual election held this 

 day was read, and the following named officers were declared 



* I am not sure whether this is the "singular effect" thus described by 

 Brewster (loc. cit. p. 124). "In conveying the bands vertically round, the 

 neutral line, in place of crossing them at a right angle, was the arc of a circle, 

 to which one of the bands was a tangent." (See also pp. 121, 167.) 



