112 E.. C. Pickering—Measurements of the 
the plane passing through the sun, and hence be parallel to the 
plane of polarization. Five series of observations were made 
in this way, all tending to show that the polarization was inde- 
pendent of the distance of the point to the right or left of the 
plane eon through the sun. The results are given in Table 
IV, in which the first column gives the number of the series, 
the second the sun’s altitude, the third its distance from the 
points observed, the fourth the number of the latter, and the 
fifth their mean polarization. 
TABLE 1V.—Polarization of points equidistant from the sun. 
Series. Alt. Dist. Theo, Pol’n. 
12 5° 90° 9 T6°T 
13 20° 60 6 42°9 
14 48° 90° 8 65°4 
45° 60° 10 41°7 
49° 120 2 43°4 
40° 30° 8 10°7 
15 40° 90° 10 60°4 
41° 120° 9 40°9 
43° 60° 10 34°2 
16 —5° 90° 6 T7°D 
One series, the first, is given in full in Table V, to show the 
amount of variation of the different points observed. 
LE V.—Series 12. July 15. 
Bae Distance 90°, Altitude 5°. 
M.D. Pol: 
15 78° 
60 14:3 
45 19°8 
30 77-0 
0 77-2 
30 74°8 
45 75°2 
60 716°8 
75 768 
Mean * > . ee 
All these observations point to one very remarkable rent: 
namely, that the polarization is the same for a He solar 
distance for any meridian distance ; in ee words, that the 
polarization is the same for all points equally distant from the 
sun. The variations in the observations are to be ascri 
partly to errors of observation and partly to real irregularities 
in the atmosphere, as it is evident that they follow no regular 
law. The means therefore give us the true polarization with 
much greater accuracy. ey are represented in fig. 5 b 
small crosses. The next thing is to determine the law which 
connects the polarization with the solar distance in all these 
