
PHENOMENA OF THE ZODIACAL LIGHT. 499 
1831, particularly if, as it has been said, the lightest part of these singular twi- 
lights did not coincide with the place of the sun below the horizon.” 
Sir Joun HerscHeEv’s views, published only five years ago, were called forth 
by the tail of the great comet of 1843 having been by some so pertinaciously 
mistaken for the zodiacal light. 
“ The zodiacal light,” said he, “as its name imports, invariably appears in 
the zodiac, or, to speak more precisely, in the plane of the sun’s equator, which is 
7 inclined to the zodiac, and which plane, seen from the sun, intersects the ecliptic 
in longitude 78° and 258°, or so much in advance of the equinoctial points. In 
consequence, it is seen to the best advantage at, or a little after, the equinoxes, 
after sunset at the spring, and before sunrise at the autumnal equinox, not only 
because the direction of its apparent axis lies at those times more perpendicular 
to the horizon, but also because at those epochs we are approaching the situation 
in which it is seen most completely in section. 
“ At the vernal equinox, the appearance of the zodiacal light is that of a pretty 
broad pyramidal, or rather lenticular, body of light, which begins to be visible as 
soon as the twilight decays. It is very bright at its lower or broader part near 
the horizon, and (if there be broken clouds about) often appears like the glow of 
a distant conflagration, or of the rising moon, only less red; giving rise, in short, 
to amorphous masses of light, such as have been noticed by some as possibly ap- 
pertaining to the comet. At higher altitudes its light fades gradually, and is seldom 
traceable much beyond the Pleiades, which it usually however attains and in- 
volves; and (what is most to my present purpose) its axis at the vernal equinox is 
always inclined (to the nortward of the equator) at an angle of between 60° and 
70° to the horizon; and it is most luminous at its base, resting on the horizon, 
_ where also it is broadest, occupying, in fact, an angular breadth of somewhere 
about 10° or 12° in ordinary clear weather.” 
The ring hypothesis of Cassini has, however, been followed in a greater or 
less degree, by La Puace, ScuEersert, and Porsson, as well as by Humsotp7, 
_ who is an observer, and publishing in 1844 is the latest of all the authorities. 
His description of the general appearance of the light is most vivid and truth- 
ful, and can perhaps only be fully appreciated by those who have seen it under 
similar favourable circumstances. 
‘« Those who have dwelt long,” says he, “ in the zone of Palms, must retain 
a pleasing remembrance of the mild radiance of this phenomenon, which, rising 
pyramidally, illumines a portion of the unvarying length of the tropical nights. 
~ [have seen it occasionally shine with a brightness greater than that of the milky 
way, near the constellation of Sagittarius ; and this not only in the dry and highly 
rarified atmosphere of the summits of the Andes, at elevations of thirteen to 
fifteen thousand feet, but also in the boundless grassy plains or Manos of Venezuela, 
and on the sea-coast under the ever-clear sky of Cumana. The phenomenon is 
