rarely forms a ball or flies in one
compact mass: every single shot follows its
own independent trajectory, and the charge
spreads.

Besides this, the observations and
calculations made on the course of the comet's
nucleus, indicate that it, the nucleus, has an
elliptical orbit with a period of about twenty-
one centuries.  But all the particles which
may have acquired even moderate
accelerations, would necessarily assume hyperbolical
orbits.  An ellipse, or oval, is a curved line
which returns into itself, like a circle, and
might equally, like it, be taken for an emblem
of eternity.  A hyperbola is a sort of oval
with one end burst open and the lines
imperfectly straightened, so that there is no return
into itself.  It is a curve which may be
roughly compared to a pair of sugar-tongs
with never-ending, legs, distended by a large
lump of sugar: for a hyperbola's legs may be
lengthened, or may extend, infinitely.
Consequently, if any cause breaks open a comet's
elliptical orbit, or the elliptical orbit of any
of its non-coherent portions so as to pull and
wring it into a hyperbola, there is no more
return possible for that comet, or that portion
of a comet.  Now, when we remember the
immense length of a comet, it is clear that
the perturbations of the planets, acting
unequally on the different portions of a comet,
in consequence of their unequal distances,
are certainly sufficient to give them diverging
orbits.  The materials of the tail are thus
dissipated for ever, or nearly so.  Therefore,
could we even live one-and-twenty centuries,
take Donati's comet, we ne'er shall look upon
its like again; even if we saw its professed self.
Finally, Donati's comet appears to have
experienced, at its perihelion, powerful physical
actions from the solar heat.  These actions
must have accelerated the particles of one-half
of the nucleus, and retarded those of the other
half; so that the former would take orbits of
longer period, or even hyperbolical orbits,
whilst the period of the latter would be
shortened.  Donati (who is about to publish
drawings of his comet in its different phases)
himself says, that there can be no doubt that
the sun successively detached matter from
the comet's head, which matter was afterwards
dispersed by taking its departure from
the nucleus, to constitute the hairy portion
and the tail of the star.  A comet would
thus be a magnificent firework, which would
burn itself out and become dissipated by the
very act of its display.

From the motion of comets which describe
hyperbolical orbits, Monsieur Brento
ingeniously calculates the direction and the greatness
of the sun's motion of translation through
space.  It would appear that, at the present
moment, the sun's velocity of translation,
instead of being great and proportional to the
magnitude and importance of that heavenly
body, is scarcely equal to the sixth of that
of the earth in her orbit.

Professor Govi, one of Donati's friends,
ascertained, in the first place, the polarisation
of the comet's light, confirming what Arago
had observed in eighteen hundred and thirty-
five in Halley's comet; secondly, he determined
the position of the plane of polarisation
of this light, whose trace coincided
sensibly with the axis of the tail.  This
coincidence continued to exist till the tenth of
October; after which date bad weather
prevented the comet's being observed for
some time.  This position of the plane of
polarisation in reference to the position of
the sun, removes all doubt as to the source of
at least the most considerable portion of the
light with which the comet shone,—namely,
that it was derived from the sun.

These are not the only nor the least
considerable chips that have fallen from the
comet and its predecessors.  Our readers will
recollect that the existence of the ether (if
demonstrated) was demonstrated by a comet.*
It had been previously rendered probable,
and has since been confirmed, by calculations
based on the undulatory theory of light as a
hypothesis, and by their accordance with
actual phenomena.  The discovery of the
phenomena of interference, in which two
lights, by mingling with each other,
reciprocally annul each other's effects; that of the
polarisation of light, which renders its rays
susceptible of being reflected without being
refracted in a certain plane for that particular
ray, and susceptible, on the other hand, of
refraction and not of reflection in another plane
holding a special relation to the first.  These
two grand discoveries of modern natural
philosophy have compelled mathematicians to
recognise, in light, a series of undulations
which are propagated in an eminently elastic
fluid, named by them, as we know, the ether.
And then the retardation which the
propagation of light suffers by passing through
bodies endowed with the highest refracting
powers (well established by diverse
experiments) gives strong support to this view of
the nature of light.  But further: from the
notion of a repulsive ether, Monsieur Brento
has deduced a sublime consequence, and has
thus made a comet the parent, or rather the
ancestor, of a new proof of the infinity of the
created universe.

* See page 464 of the present volume.

In the first place; since the light and heat
of the stars can only reach us by the agency
of the ether, it follows that this fluid must
fill the whole of the celestial space in which
the stars perform their movements.  Secondly,
as everything indicates that the movement of
the stars in the firmament do not meet with
any sensible resistance, it follows that the
density of the ether which they traverse
must be indefinitely small in comparison
with that of the stars; lastly, since the light
of the stars evidently reaches us in straight
lines, it follows that the density of the ether