ng planets
float. The resisting medium which opposes its journey may be merely an
ethereal solar atmosphere surrounding the sun, as our air surrounds
the earth, but spreading to distances of millions instead of tens of
miles. On the other hand, it must be remembered also that starlight
passes through universal space, and is everywhere spread out therein,
and that it is hardly possible to think of starlight as an existence
without some sort of material reality. Some physicists believe that
Encke's Comet, with its retarded motions, will some day fall into the
sun; while others fancy that such a consummation can never take place,
because successive portions of its substance will be thrown off by the
tail-forming process with each perihelion return; so that long before
the cometic mass could reach the sun, it will have been altogether
dissipated into space, and nothing will be left to accomplish the
final state of the fall.

The great peculiarity of cometic paths, as compared with the planetary
ones, is, that they consist of ellipses of very much more eccentric
proportions; and that, therefore, the bodies moving in them, go
alternately to much greater and less distances from the sun than the
planets do. It must not be imagined, however, that all comets revolve
about the sun even in the most lengthened ellipses. Three at
least--the comets of 1723, 1771, and 1818--are known to have moved
along hyperbolic paths instead of parabolic or elliptical ones. These
comets, therefore, can make but one appearance in our skies. Having
once shewn themselves there, and vanished, they are lost to us for
ever. They are but stray and chance visitors to the domains of our
sun, and refuse to submit themselves, with the more regular members of
their fraternity, to the regulation-arrangements of our system, or to
appear punctually at the systematic roll-call therein instituted. They
are the true free-wanderers of the Infinite, passing from shore to
shore of immensity, and presenting themselves, for short and uncertain
intervals, to star after star. When they flit through our skies, they
shew themselves in all possible positions, and move along all possible
directions. They sometimes, however, yield too much to temptation, and
have to suffer the penalty of a short imprisonment in consequence.
Lexell's Comet, for instance, rushed in its hyperbolic path too near
to Jupiter, and was caught in the attraction of its mass, and made to
dance attendance