ecome visible about that time, a very close
appulse is possible. It is not unlikely, also, that if the elements of
Pallas were so far perfected as to afford reliable indications, that the
near approach of the comet might thus be heralded in advance, and lead
to an earlier detection of its presence. Would it not be a worthy
contribution to science, for some one possessing the necessary leisure,
to give an ephemeris of the planet for that epoch; as a very slight
change in Mr. Hind's elements of the comet, would cause an actual
intersection of the two orbits in about heliocentric longitude 153d? The
subsequent nodal passage of Pallas will take place near opposition, and
be very favorably situated for determining the instant of its passage;
and, of all the elements, this would be more likely to be affected than
any other.[47]

THE ZODIAL LIGHT.

A phenomenon, akin to that which we have just been considering, is
presented by that great cone of diffused light which accompanies the
sun, and which in tropical climes displays a brilliancy seldom witnessed
in high latitudes, on account of its greater deviation from the
perpendicular. Sir John Herschel conjectures that it may be "no other
than the denser part of that medium, which, as we have reason to
believe, resists the motion, of comets,--loaded, perhaps, with the
actual materials of the tails of millions of those bodies, of which they
have been stripped in their successive perihelion passages, and which
may be slowly subsiding into the sun." If these materials have been
stripped, it is due to some force; and the same force would scarcely
permit them to subside into the sun. Once stripped, these portions must
be borne outwards, by the radial stream, to the outer verge of the
system. Still, there are, no doubt, denser particles of matter, of the
average atomic density of Mercury and Venus, which can maintain their
ground against the radial stream, and continue to circulate near the
central plane of the vortex, in all that space between the earth and the
sun. But if the zodial light be the denser part of that medium, which
astronomers now generally recognize as a resisting medium, how happens
it that it should be confined to the plane of the ecliptic? Why should
it not be a globular atmosphere? Here, again, our theory steps in with a
triumphant explanation; for while it permits the accumulation of such
particles around the equatorial plane of the sun, it allows no
resting-pl