438 A. C. Lewis—Zodiacal Light. 
phere is thus obtained. In all cases the observations were made 
in perfect darkness, and recorded as soon after as possible. 
Nearly all of the observations were made in Germantown, 
Pa. (lat, 40°); but a few, especially those upon the “ horizon 
light,” were made at the sea-shore, on board ship, or on the 
mountains. 
The zodiacal light may be divided into three portions :—the 
Zodiacal Cone, the Zodiacal Band and the Gegenschein. This 
division, in addition to its convenience, saves confusion in 
In this latitude, the zodiacal cone is not a symmetrical figure, 
its southern side being more vertical than its northern side. 
southern side is also the more sharply defined of the two, and 
is the side more nearly parallel with the ecliptic. Its axis of 
greatest brightness does not correspond with its axis of sym- 
metry, but lies south of it. There is a very small angle be- 
tween these twoaxes. The axis of greatest brightness appears 
to lie precisely upon the ecliptic. The lateral extension of the 
base of the zodiacal cone, often observed, is probably a purely 
atmospheric effect. 
The brightness of the zodiacal cone depends upon the sea- 
son of the year and the time of the night when observed. I 
brillianey increases rapidly as it approaches the sun, and at 
such times as it can be seen nearest the sun it always appears 
brightest. The time of shortest twilight coincides with the 
greatest brilliancy of the zodiacal cone. In each of the five 
years the evening zodiacal cone was most brilliant from the 
middle of February to the middle of March. Several observa- 
tions have proved it to cast a distinct shadow at that time.* 
* Zodiacal light shadows were noticed on Feb. 12, 1877, at 7.15 P. M., and on 
Feb. 21, 1879, at 7.20 p. m. On the latter night snow covered the ground, on 
which distinct zodiacal light shadows were cast. 
