452 <A. W. Wright—Polarization of the Zodiacal Lrght. 
of parts of the field, or as with the double-image prism, the 
Nicol’s prism, or a bundle of glass plates set at the polarizing 
angle, by a diminution of the brightness of the object itself. 
None of them, however, gave results of any value. In resuming 
the study of thesubject some months later, the attempt was made 
to find a combination which should give a large field of view, 
and which, while absorbing as little light as possible, should 
indicate the presence of even small proportions of polarized 
light, by sufficient variations of intensity to render it available 
with the faintest visible illumination. : 
avart in which the tourmaline was replaced by a Nicol, 
though possessing almost perfect transparency, was found to 
give too small a field of view, and bands too faint to render it 
of any service. Another instrument was constructed on a plan 
owever, are inherent to this mode of investigation; one, that 
if the field is not of uniform brightness throughout, the brighter 
ties can only be found by indirect vision, the eye being turn 
to some point in the median line of the images. Although 
this instrument is capable of 
was soon abandoned for a better. : 
Among the polariscopic apparatus belonging to the phy sical 
‘cabinet of Yale College, a quartz plate was found, cut_perpe? 
dicularly to the axis, and exhibiting by polarized light a” 
unusual intensity of color. It is a macle, the body of the plate 
consisting of left-handed quartz, through which passes some 
what excentrically a band of right-handed quartz, 6°5 millimeter 
breadth. This band is not bounded by sharp lines ° 
division on the sides, but by intermediate strips (0 4 in ed 
figures), about two millimeters in breadth, which are of ane 
ent structure, and are apparently formed by the interleaving © 
the strata of the two portions at their edges. In the polarizing 
apparatus these strips simply vary from bright to dark, without 
ee _ * Phil. Mag., vol. xliii, 1872, p. 382. 
