456 <A. W. Wright—Polarization of the Zodiacal Light. 
experimentally, and showed that the deviation from theory in 
the case of four plates only becomes perceptible above 65°. 
As Prof. Pickering used the value “=1°55, the numbers in his 
table are slightly greater than those used in constructing the 
curve, from Prof. Adams’s tab 
brightness as it had with the zodiacal light. A small scrate 
upon the quartz plate, which could just be seen by the light of 
the latter, served as a means of control in adjusting the inten- 
sity. The experiments being conducted as before, gave, as the 
mean of numerous determinations, the angle 36°°6, correspond- 
ing to a proportion of 16 per cent, which is probably not far 
from the true value of the amount sought. Another, in which 
the light was made perceptibly brighter than that of the zodiacal 
tract, gave for the angle 28°°5, and a percentage of 9°4, which 1s 
certainly too small. We may safely take 15 per cent as near 
the true value. 
_ The fact of polarization implies that the light is reflected, 
either wholly or in part, and is thus derived originally from the 
su e latter supposition is fully confirmed by various 
spectroscopic observations, of M. Liais,* Prof. C. Piazzi-Smy th,t 
and others, which show that the spectrum is continuous, and 
not perceptibly different from that of faint sunlight The 
writer has made numerous observations with a spectTo- 
Scope specially arranged for faint light, of which an accouvt 
. | Tom. 74, . 262. 
+ Monty Notices of the ies Age Gon, June, 1872, p. 277. 
