auses, unknown to us,
might account for it. Subsequent and more exact calculations fail
to find any retardations in at least two revolutions between 1865
and [Page 131] 1871. Indications point to a retardation of one and a
half hours both before and since. But such discrepancy of result
proves nothing concerning a resisting medium, but rather is an
argument against its existence. Besides, Faye's comet, in four
revolutions of seven years each, shows no sign of retardation.

The truth may be this, that a kind of atmosphere exists around the
sun, perhaps revealed by the zodiacal light, that reaches beyond
where Encke's comet dips inside the orbit of Mercury, and thus
retards this body, but does not reach beyond the orbit of Mars,
where Faye's comet wheels and withdraws.

_Of what do Comets consist?_

The unsolved problems pertaining to comets are very numerous and
exceedingly delicate. Whence come they? Why did they not contract to
centres of nebulae? Are there regions where attractions are balanced,
and matter is left to contract on itself, till the movements of
suns and planets adds or diminishes attractive force on one side,
and so allows them to be drawn slowly toward one planet, and its
sun, or another? There is ground for thinking that the comet of
1866 and its train of meteors, visible to us in November, was thus
drawn into our system by the planet Uranus. Indeed, Leverrier has
conjecturally fixed upon the date of A.D. 128 as the time when it
occurred; but another and closer observation of its next return,
in 1899, will be needed to give confirmation to the opinion. Our
sun's authority extends at least half-way to the nearest fixed star,
one hundred thousand times farther than the orbit of the earth.
Meteoric and cometary matter lying [Page 132] there, in a spherical
shell about the solar system, balanced between the attraction of
different suns, finally feels the power that determines its destiny
toward our sun. It would take 167,000,000 years to come thence to
our system.

The conditions of matter with which we are acquainted do not cover
all the ground presented by these mysterious visitors. We know
a gas sixteen times as light as air, but hydrogen is vastly too
heavy and dense; for we see the faintest star through thousands of
miles of cometary matter; we know that water may become cloudy vapor,
but a little of it obscures the vision. Into what more ethereal,
and we might almost say spiritual, forms matter