manner supposed by Arrhenius' hypothesis is evident enough; and it
will be observed that the new theory, after all, is only another
variant of the older one which attributes the Zodiacal Light to an
extension of the solar corona. But it differs from the older theory in
offering an explanation of the manner in which the extension is
effected, and it differentiates between the corona proper and the
streams of negative particles shot away from the sun. In its details
the hypothesis of Arrhenius also affords an explanation of many
peculiarities of the Zodiacal Light, such as that it is confined to
the neighborhood of the ecliptic, and that it is stronger on the side
of the earth which is just turning away from a position under the sun
than on the other side; but it would carry us beyond our limits to go
into these particulars. The Gegenschein, according to this theory, is
a part of the same phenomenon as the Zodiacal Light, for by the laws
of perspective it is evident that the reflection from the streams of
particles situated at a point directly opposite to the sun would be at
a maximum, and this is the place which the Gegenschein occupies. Apart
from its geometrical relations to the position of the sun, the
variability of the Zodiacal Light appears to affirm its solar
dependence, and this too would be accounted for by Arrhenius'
hypothesis better than by the old theory of coronal extension. The
amount of corpuscular discharge from the sun must naturally be
governed by the state of relative activity or inactivity of the
latter, and this could not but be reflected in the varying splendor of
the Zodiacal Light. But much more extended study than has yet been
given to the subject will be required before we can feel that we know
with reasonable certainty what this mysterious phenomenon really is.
By the hypothesis of Arrhenius every planet that has an atmosphere
must have a Zodiacal Light attending it, but the phenomenon is too
faint for us to be able to see it in the case, for instance, of Venus,