This shorter tail is due to the particles that we have
just spoken of as being driven sunward from the earth by the action of
ultra-violet light. No doubt this whole subject is too technical for
popular statement; but at any rate the general reader can understand
the picturesque side of the theory, for its advocates assure us that
if we were on the moon we would doubtless be able to see the
comet-like tails of the earth, and then we could appreciate the part
that they play in producing the phenomenon of the Zodiacal Light.
That the Light as we see it could be produced by the reflection of
sunlight from swarms of particles careering round the earth in the
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.
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