l, must be
admitted to run out to a great depth on either side from the sun, and
reach far into that unoccupied space intervening between our system and
the nearest fixed stars, and from these opposite points the solar vortex
is supplied with that stream of ether which passes down either pole to
restore a partial equilibrium in the density of the ether of the vortex,
rarefied by centrifugal force. As certain portions of the heavens are
crowded with stars, and other parts comparatively vacant, we may expect
a similar inequality in the distribution of that cometic dust, which
causes a certain amount of extinction in the light of the stars, and,
therefore, seeing that the two extremities of the axis of the solar
vortex are so widely separated, it would not be wonderful if different
quantities of such matter were brought down into the vortex from these
extremities.

From recent observations made by H. R. Birt, at the observatory of the
British Association, it would appear that the brightest portion of the
zodial light is always north of the ecliptic. Others have also remarked
the same, and if we couple this fact with the suggestion just made, we
are justified in suspecting that a greater quantity of cometic dust
comes down the northern pole of the vortex than down the southern. This
matter, in passing outward, does not, of course, immediately attain to
the central plane of the vortex, but is more thickly distributed along a
plane parallel to this plane. And the same will be observed by that
matter coming down the southern pole; it will be, in a certain degree,
retained in a plane south of the central plane, but still parallel with
it. This would account for the greater brightness of the northern side
of the zodial light. It would, also, account for the greater frequency
of meteors in summer and autumn than in the opposite seasons. From May to
November the earth is above the central plane of the vortex, and,
consequently, on the northern side; but after passing the node in
November, she is on the under or southern side, and the meteors are less
frequent. With this general explanation we shall close. If what we have
advanced be an approximation to the truth, the theory itself affords
ample indications of what observations are requisite to prove or
disprove it; and, on this account, a theory is of great benefit, as
suggestive of many questions and combinations of facts which otherwise
might never be thought of.

We have thus