of the Atmosphere. 453 



Corresponding degrees of rotation 

 or polarization, or values of R. 



6-813 



1-626 



2-439 



3-252 



4-065 



4-878 



6-504 



8-130 



9-756 



11-382 



13-008 



14-634 



16-260 



17-886 



19-Sil 



21-137 



22-764 



24-396 



26-016 



27-642 



29-268 



30-000 



Hence the maximum polarization of the atmosphere, as 

 measured by a rotation of 30°, is equal to that produced by 

 reflexion from a plate of glass at an angle of 65^°, and with a 

 refractive index of r4826, or to that produced by a surface 

 of diamond at an angle of 75^°. The number of refractions 

 at a given angle, or the angle, with a given number of plates 

 of glass, at which a rotation of 30° is produced, will be found 

 from the formula in my paper on the Compensations of Po- 

 larized Light*. 



As the sun rises above the horizon, the lines of equal pola- 

 rization change their form, and the degree of polarization 

 varies at points of the sky whose distance from the sun is in- 

 variable. The neutral points above and below the sun approach 

 •his disc till he reaches the meridian, when the distance of each 

 from the sun is a minimum ; they then separate again, and 

 attain their maximum distance, when he reaches the horizon. 

 In countries where the sun passes across the zenith, these two 

 neutral points coincide with the sun, when he reaches the 

 zenith, and again separate. 



• Transactions of the Royal Irish Academy, vol. xix. part 2. p. 13. 



