Barnard. I recall an attempt to see it under his guidance during a
visit to Mount Hamilton, when he was occupied there with the Lick
telescope. Of course, both the Gegenschein and the Zodiacal Light are
too diffuse to be studied with telescopes, which, so to speak, magnify
them out of existence. They can only be successfully studied with the
naked eye, since every faintest glimmer that they afford must be
utilized. This is especially true of the Gegenschein. At Mount
Hamilton, Mr Barnard pointed out to me its location with reference to
certain stars, but with all my gazing I could not be sure that I saw
it. To him, on the contrary, it was obvious; he had studied it for
months, and was able to indicate its shape, its boundaries, its
diameter, and the declination of its center with regard to the
ecliptic. There is not, of course, the shadow of a doubt of the
existence of the Gegenschein, and yet I question if one person in a
million has ever seen or ever will see it. The Zodiacal Light, on the
other hand, is plain enough, provided that the time and the
circumstances of the observation are properly chosen.

In the attempts to explain the Zodiacal Light, the favorite hypothesis
has been that it is an appendage of the sun -- perhaps simply an
extension of the corona in the plane of the ecliptic, which is not
very far from coinciding with that of the sun's equator. This idea is
quite a natural one, because of the evident relation of the light to
the position of the sun. The vast extension of the equatorial wings of
the corona in 1878 gave apparent support to this hypothesis; if the
substance of the corona could extend ten million miles from the sun,
why might it not extend even one hundred million, gradually fading out
beyond the orbit of the earth? A variation of this hypothesis assumes
that the reflection is due to swarms of meteors circling about the
sun, in the plane of its equator, all the way from its immediate