454 A. W. Wright—Polarization of the Zodiacal Lrght, 
longer diagonal of the Nicol is in that plane; when the bands 
are dark, the plane of polarization is parallel to the shorter 
diagonal. 
On the completion of the instrument the first’ favorable 
opportunity was improved to test its efficiency upon the zodiacal 
h t was almost immediately found to indicate the exist- 
ence of light polarized in a plane passing through the sun. 
The bands were fainter than had been expected, and at first 
were overlooked. More careful attention, however, and the 
observance of suitable precautions established their presence 
beyond a doubt. The observations were made in a room in the 
upper floor of one of the college buildings, the windows of which 
look toward the southwest, and command a clear view nearly 
to the horizon. The room during the observations received 
light only from the sky, which sufficed to render objects dimly 
visible. After being exposed only to this dim light for fifteen 
or twenty minutes, the eye became sufficiently sensitive for 
observation. This was a very necessary precaution, as a 
moment’s exposure to a bright light rendered the eye unfit for 
delicate discrimination of luminous intensities for a long time. 
sponcling to an inclination of 45° in the Nicol, less easily, and 
the dark bands (6 4, figure 2) by glimpses, After determining; 
by repeated observations, the angle made by each of the bancs 
with some fixed line, as the axis of the zodiacal light, or 4 wes 
nearly parallel to it drawn between two known stars, the post 
tion of the plane of polarization was found, by means of light 
a suitable position, or by observing the position of the Nicol. 
The reults of the numerous phair vations of differcht evenings 
