138 ROCHESTER ACADEMY OF SCIENCE. [Jan. 26, 
exceptionally favorable circumstances this band has been traced com- 
pletely across the sky. In that portion of it which is most remote from 
the sun there has been found a spot brighter than the rest, which has 
been called the gegenschein. The zodiacal light is brightest in the 
tropics, and in that location has been thought by some to exhibit pulsa- 
tions. Its-spectrum however is usually continuous, indicating that it 
shines by reflected sunlight. Auroral or other lines have been detected 
in its spectrum only exceptionally and under such circumstances that 
they may perhaps have been due to intermixture of light from other 
sources. 
In the middle latitudes the zodiacal light is brightest in March and 
October, in the former case after sunset, and in the latter before sunrise. 
At these times one margin of the band is better defined than the other, 
and more exactly included within the plane of the ecliptic. At other 
seasons there is decreasing brightness, and both edges become ill 
defined. It does not seem possible to explain these differences fully 
by referring them to variations in the angle made with the horizon, or 
to the interference of twilight. The peculiarities mentioned, and others 
yet to be described, are consistent with the idea that the zodiacal light 
is a visible extension of the solar corona. 
This extension of the corona is probably double, corresponding to 
the bifurcation seen during eclipses, each section overlying a sunspot 
belt. It consists doubtless of meteoric particles of the usual ferruginous 
character, moving in definite orbits, and shining by reflected light. It 
is a solar appendage, but not a part of the sun’s atmosphere. Like the 
rings of Saturn, it does not conform to the plane of the earth’s orbit 
but to that of the equator of the body which it surrounds, which in this 
case is the sun itself. As viewed from the earth these coronal exten- 
sions are at times foreshortened, and at times opened out, so as to 
become more plainly visible. In the spring months the south pole of 
the sun is inclined toward the earth, so that the latter is almost exactly 
in the heliocentric zenith of the southern sunspot belt and coronal 
extension. Consequently the particles composing this extension are in 
a direct line between sun and earth, and shining as they do by reflected 
light, like the new moon, they become almost invisible. Coincidently 
the coronal extension overlying the northern sunspot belt is opened out 
to its widest extent, and reflects more light earthward than at any other 
time. Hence if these extensions become visible as the zodiacal light, 
the southern edge at this season should be the more sharply defined, 
and more exactly include within the plane of the ecliptic, because of 
the lack of illumination described, and the northern edge on the other 
