442 H. C. Lewis—Zodiacal Light. 
this width is apparently greatly increased, and, the horizon 
light interfering, the whole southern sky beneath the Via Lac- 
tea may seem illuminated. On rare occasions it is possible to 
detect an inner zone of greater brightness, some 2° wide. At 
such times the principal band of light has a width of 5°-6°, 
while beyond and on either side a very diffuse portion meas- 
ures from edge to edge as much as 20°. This diffuse portion 
is particularly noticeable on the northern edge. It must be 
understood that each of these portions shade by insensible de- 
grees one into the other, and that probably no two observers 
would give the same widths. 
The zodiacal band lies in the zodiac, upon or close to the 
ecliptic. The observations appear to show that while its axis 
of greatest brightness is either on or very slightly north of the 
ecliptic, the axis of symmetry is decidedly north of that line. 
Probably in the southern hemisphere the reverse would be the 
case. 
The zodiacal band is generally quite obscured in the pres- 
ence of the moon, but two or three observations are recorded, 
in which the zodiacal band has apparently been seen by moon- 
light. That such an extremely faint object as the zodiacal 
band should be seen by moonlight, as though illuminated by 
it, is an interesting fact, which, however, is not as yet sus- 
tained by sufficient observation. 
2 Gegenschein.—The term gegenschein, given by Brorsen 
to a light which appears opposite to the sun, but which has 
been confused by others with the eastern part of the zodiacal 
band, is here limited to the round or oval spot of light which 
nightly appears at that place in the zodiacal band which is 
180° from the sun. 
The writer has paid particular attention to the observation 
and careful mapping of this object. He has made more than 
forty maps of its position among the stars at different times, and 
upon subsequent calculation, he has found that almost without 
exception, the center of the gegenschein, thus mapped, lies 
within 1° or 2° of a point in the heavens 180° in longitude 
from the sun. 
The gegenschein is an extremely faint spot of light some 7° 
in diameter, lying in the zodiacal band. It is best placed for 
observation about midnight, and can be detected by shifting 
the eye backward and forward along the zodiacal band. Any- 
one who looks for it in February and March, when the Via 
Lactea is low on the horizon, cannot fail to find it, first in 
Leo and afterwards in Virgo. Night after night it shifts its 
place among the stars, so as to keep opposite to the sun. It is 
of course invisible when crossing the Via Lactea. : 
The gegenschein is decidedly brighter than the zodiacal 
