But will not the admission of a vorticose motion of the ethereal medium,
affect the aberration of light? It is well known that the question has
been mooted, whether the velocity of reflected light is the same as that
of direct light. The value of aberration having been considered 20".25,
from the eclipses of Jupiter's satellites, while later determinations,
from observations on Polaris, give 20".45. It cannot be doubted that
light, in traversing the central parts of the solar vortex, that is,
having to cross the whole orbit of the earth, should pass this distance
in a portion of time somewhat different to a similar distance outside
the earth's orbit, where the density is greater, and consequently induce
an error in the aberration, determined by the eclipses of Jupiter's
satellites. In the case of Polaris, the circumstances are more equal;
still, a difference ought to be detected between the deduced aberration
in summer and in winter, as, in the first case, the light passes near
the axis of the solar vortex, where (according to the theory) a change
of density occurs. This is an important practical question, and the
suggestion is worthy attention. Now, the question occurs, will light
pass through the rarefied space with greater velocity than through the
denser ether beyond? From recent experiments, first instituted by Arago,
it is determined that light passes with less velocity through water than
through air; and one result of these experiments is the confirmation
they give to the theory of Fresnel, that the medium which conveys the
action of light partly partakes of the motion of the refracting body.
This of itself is a strong confirmation of this theory of an ethereal
medium. It may also be remarked, that every test applied to the
phenomenon of light, adds additional strength to the undulatory theory,
at the expense of the Newtonian theory of emission. As light occupies
time in traversing space, it must follow from the theory that it does
not come from the radiant point exactly in straight lines, inasmuch as
the ether itself is in motion tangentially,--the velocity being in the
sub-duplicate ratio of the distances from the sun inversely.
May not that singular phenomenon,--the projection of a star on the
moon's disc, at the time of an occultation,--be due to this curvature of
the path of a ray of light, by considering that the rays from the moon
have less intensity, but more mechanical momentum, and consequently
more power to keep a straight direction? Let us explain: we have urged
that light, as well as heat, is a mechanical effect of atomic motion,
propagated through an elastic medium; that, _ceteris paribus_, the
product of matter by its motion is ever a constant quantity for equal
spaces throughout the universe,--in a word, that it is, and must
necessarily be, a fundamental law of nature. All departures from this
law are consequences of accidental arrangements, which can only be
considered of temporary duration. Our knowledge of planetary matter
requires the admission of differences in the density, form, and size of
ultimate atoms, and, according to the above law, when the atoms are of
uniform temperature or motion, the product of the matter of each by its
motion, when reduced to the same space, will be constant. The momentum
of two different atoms, therefore, we will consider equal, for the sake
of illustration; yet this momentum is made up of two different
elements,--matter and motion. Let us exaggerate the difference, and
assign a ratio of 1000 to 1. Suppose a ball of iron of 1000 lbs.,
resting upon a horizontal plane, should be struck by another ball of 1
lb., having a motion of 1000 feet in a second, and, in a second case,
should be struck by a ball of 1000 lbs., having a velocity of 1 foot per
second, the momentum of each ball is similar; but experience proves that
the motion impressed on the ball at rest is not similar; the ponderous
weight and slow motion is far more effective in displacing this ball,
for the reason that time is essential to the distribution of the motion.
If the body to be struck be small as, for instance, a nail, a greater
motion and less matter is more effective than much matter and little
motion. Hence, we have a _distinction_ applicable to the difference of
momentum of luminous and calorific rays. The velocity of a wave of sound
through the atmosphere, is the same for the deep-toned thunder and the
shrillest whistle,--being dependent on the density of the medium, and
not on the source from which it emanates. So it is in the ethereal
medium.
This view is in accordance with the experiments of M. Delaroche and
Melloni, on the transmission of light and heat through diaphanous
bodies--the more calorific rays feeling more and more the influence of
thickness, showing that more motion was imparted to the particles of the
diaphanous substance by the rays possessing more material momentum, and
still more when the temperature of the radiating body was low, evidently
analogous to the illustration we have cited. Light may therefore be
regarded as the effect of the vibration of atoms having little mass, and
as this mass increases, the rays become more calorific, and finally the
calorific effect is the only evidence of their existence; as towards the
extreme red end of the spectrum they cease to be visible, owing to their
inability to impart their vibrations to the optic nerve. This may also
influence the law of gravitation. In this we have also an explanation of
the dispersion of light. The rays proceeding from atoms of small mass
having less material momentum, are the most refrangible, and those
possessing greater material momentum, are the least refrangible; so that
instead of presenting a difficulty in the undulatory theory of light,
this dispersion is a necessary consequence of its first principles.
It is inferred from the experiments cited, and the facts ascertained by
them, viz.: that the velocity of light in water is less than its
velocity in air; that the density of the ether is greater in the first
case; but this by no means follows. We have advocated the idea, that the
ethereal medium is less dense within a refracting body than without. We
regard it as a fundamental principle. Taking the free ether of heaven;
the vibrations in the denser ether will no doubt be slowest; but within
a refracting body we must consider there is motion lost, or _light
absorbed_, and the time of the transmission is thus increased.
There has been a phenomenon observed in transits of Mercury and Venus
across the sun, of which no explanation has been rendered by
astronomers. When these planets are visible on the solar disc, they are
seen surrounded by rings, as if the light was intercepted and increased
alternately. This is no doubt due to a small effect of interference,
caused by change of velocity in passing through the rarefied nucleus of
these planetary vortices, near the body of the planet, and through the
denser ether beyond, acting first as a concave, and secondly as a convex
refracting body; always considering that the ray will deviate _towards_
the side of least insistence, and thus interfere.
That heat is simply atomic motion, and altogether mechanical, is a
doctrine which ought never to have been questioned. The interest excited
by the bold experiments of Ericson, has caused the scientific to
_suspect_, that heat can be converted into motion, and motion into
heat--a fact which the author has considered too palpable to deny for
the last twenty years. He has ever regarded matter and motion as the two
great principles of nature, ever inseparable, yet variously combined;
and that without these two elements, we could have no conception of
anything existing.
It may be thought by some, who are afraid to follow truth up the rugged
precipices of the hill of knowledge, that this theory of an
interplanetary plenum leads to materialism; forgetting, that He who made
the world, formed it of matter, and pronounced it "very good." We may
consider ethereal matter, in one sense, _purer_ than planetary matter,
because unaffected by chemical laws. Whether still purer matter exists,
it is not for us to aver or deny. The Scriptures teach us that "there is
a natural body and there is a spiritual body." Beyond this we know
nothing. We, however, believe that the _invisible_ world of matter, can
only be comprehended by the indications of that which is visible; yet
while humbly endeavoring to connect by one common tie, the various
phenomena of matter and motion, we protest against those doctrines which
teach the eternal duration of the present order of things, as being
incompatible with the analogies of the past, as well as with the
revelations of the future.