ae E. C. Pickering—Measurements of the 
Art. XIV.—Measurements of the Polarization of the Lnght re- 
flected by the Sky, and by one or more plates of glass; by Prof. 
EpWwarp C. PICKERING. 
THE following observations, which will be published in full in 
the Proceedings of the American Academy of Arts and Sciences, 
were conducted to test Fresnel’s formula for the reflection of 
light. He showed that if the light was polarized in the plane of 
sin? (i—r) 
sin? (¢+7)’ 
if polarized in a plane perpendicular to it, the proportion 
incidence, the amount reflected would be A= while, 
2 
would be B = ane TERY zand r representing the angles of 
incidence and refraction respectively. Natural light may be 
regarded as composed of two equal beams pola -_ at right 
* (7) 
angles, hence the amount reflected R=3(A + B)= (= sin? (7 (pr) 
aera a formula which may be applied to any special 
case, by substituting proper values for¢ andr. The value of 
A evidently increases as 7 varies from 0° to 90°. That of B, 
on the other hand, diminishes from 0° until 7+7=90°, when 
it equals 0, or at this angle, which is that of total polarization, 
all of the ray B is transmitted, all the reflected van being 
larized in the plane of incidence. When i=90°, A=1, B=1, 
hence all the light is reflected. When 7=0°, ~ R ‘and 
equal (“ si) hence the reflected light increases with n, being 
zero when n=1, and 100 per cent when n=. Many famil- 
iar phenomena are thus readily accounted for. For instance, 
the brightness of the diamond, the covering power of white 
lead as cr paint, and the brillianey of wet or varnished stones 
and w 
rious case presents itself when n =1+ dn or differs 
from sity only by an infinitesimal amount. A then becomes 
equal to Zdn? (1+tang?2)?, and B=14dn? (1—tang?7)?._ When 
i , B, and # equal tdn?, and this quantity is accordingly 
taken as the unit in Table I. The first column gives various 
values of the angle of incidence, the second and third the 
corresponding values of A and B, the fourth the amount of 
: ion. The 
other columns will be explained hereafter. This table is 
evidently applicable to all cases where the media bounding ee 
pone have cage the same index, whether its absolu 
amount is great or s' 
