nck's comet will be absorbed into the Sun, is
probable; that all the comets of the system will be absorbed, is more
than merely possible; but, in such case, the principle of absorption
must be referred to eccentricity of orbit--to the close approximation to
the Sun, of the comets at their perihelia; and is a principle not
affecting, in any degree, the ponderous _spheres_, which are to be
regarded as the true material constituents of the Universe.--Touching
comets, in general, let me here suggest, in passing, that we cannot be
far wrong in looking upon them as the _lightning-flashes of the cosmical
Heaven_.

The idea of a retarding ether and, through it, of a final agglomeration
of all things, seemed at one time, however, to be confirmed by the
observation of a positive decrease in the orbit of the solid moon. By
reference to eclipses recorded 2500 years ago, it was found that the
velocity of the satellite's revolution _then_ was considerably less than
it is _now_; that on the hypothesis that its motions in its orbit is
uniformly in accordance with Kepler's law, and was accurately determined
_then_--2500 years ago--it is now in advance of the position it _should_
occupy, by nearly 9000 miles. The increase of velocity proved, of
course, a diminution of orbit; and astronomers were fast yielding to a
belief in an ether, as the sole mode of accounting for the phaenomenon,
when Lagrange came to the rescue. He showed that, owing to the
configurations of the spheroids, the shorter axes of their ellipses are
subject to variation in length; the longer axes being permanent; and
that this variation is continuous and vibratory--so that every orbit is
in a state of transition, either from circle to ellipse, or from ellipse
to circle. In the case of the moon, where the shorter axis is
_de_creasing, the orbit is passing from circle to ellipse and,
consequently, is _de_creasing too; but, after a long series of ages, the
ultimate eccentricity will be attained; then the shorter axis will
proceed to _in_crease, until the orbit becomes a circle; when the
process of shortening will again take place;--and so on forever. In the
case of the Earth, the orbit is passing from ellipse to circle. The
facts thus demonstrated do away, of course, with all necessity for
supposing an ether, and with all apprehension of the system's
instability--on the ether's account.

It will be remembered that I have myself assumed what we may term _an
ether_. I have