A phenomenon, akin to that which we have just been considering, is
presented by that great cone of diffused light which accompanies the
sun, and which in tropical climes displays a brilliancy seldom witnessed
in high latitudes, on account of its greater deviation from the
perpendicular. Sir John Herschel conjectures that it may be "no other
than the denser part of that medium, which, as we have reason to
believe, resists the motion, of comets,--loaded, perhaps, with the
actual materials of the tails of millions of those bodies, of which they
have been stripped in their successive perihelion passages, and which
may be slowly subsiding into the sun." If these materials have been
stripped, it is due to some force; and the same force would scarcely
permit them to subside into the sun. Once stripped, these portions must
be borne outwards, by the radial stream, to the outer verge of the
system. Still, there are, no doubt, denser particles of matter, of the
average atomic density of Mercury and Venus, which can maintain their
ground against the radial stream, and continue to circulate near the
central plane of the vortex, in all that space between the earth and the
sun. But if the zodial light be the denser part of that medium, which
astronomers now generally recognize as a resisting medium, how happens
it that it should be confined to the plane of the ecliptic? Why should
it not be a globular atmosphere? Here, again, our theory steps in with a
triumphant explanation; for while it permits the accumulation of such
particles around the equatorial plane of the sun, it allows no
resting-place very far removed from this plane. The zodial light,
therefore, is not the resisting medium, but the passage of the radial
stream through a diffuse nebula of atoms, brought down the poles of the
vortex by the polar current, and held in check along the central plane
by gravitation.
If these atoms partook of the velocity of the ether, they would not be
luminous; but being held back by gravitation, they are opposed to the
radial stream, and hence the light.
Many stars are also nebulous. In some cases we see the nebulosity
edgewise, or along the equatorial planes of the stellar vortices; in
others we look down the poles, and the nebulosities are circular, and
there is an endless variety in the shape and intensity of this light.
But the universe seems full of motion, and we are not justified in
supposing, because a star shows no such light, that it is without
rotation. The parallax of the nearest star is only one second, the whole
lenticular mass of light which surrounds our sun would therefore only
subtend an angle of a single second at the nearest fixed star. Seeing
its extreme faintness, therefore, the effulgence of the star would
render it totally invisible, provided that it _could_ traverse the vast
immensity of intervening space, without feeling the influence of that
extinction, which Struve has proved does actually diminish the number of
visible stars.
Corruscations and flickerings have also been noticed in the zodial
light, and as usual, the learned have suggested atmospheric conditions
as the cause, instead of trusting to the evidence of their own senses.
How prone is philosophy to cling to that which is enveloped in the mist
of uncertainty, rather than embrace the _too simple_ indications of
nature. As if God had only intended her glories to be revealed to a
favored few, and not to mankind at large. Blessed will be the day when
_all_ will appreciate their own powers and privileges, and no longer
regard the oracles which emanate from a professional priesthood, whose
dicta have so often tended to darken the simple counsels of truth! To
set the question of pulsations in the zodial light, as well as in the
tails of comets, at rest, only requires previously concerted
observations, in places not very widely apart; for it is scarcely
possible, that atmospheric conditions should produce simultaneous
pulsations in two distant places. If the pulsations are found to be
simultaneous, they are real; if not simultaneous, they may depend on
such conditions; but from the nature of the cause, we should look for
them as much in the zodial light, as in the aurora borealis, regarding
the different intensities.
There is also reason to suspect that the northern side is always the
brightest, both in spring and autumn. On the morning of October 4th,
1853, the light was very vivid and well defined, its northern margin
grazing Regulus and terminating at Mars, which was also to the north of
it. Now, although the _northern side_ was the brightest, the great mass
of light was to the south of the ecliptic, as far down as the cone shape
was preserved; but at 10d from the horizon, a still brighter mass
protruded from the cone towards the north, which was all _north_ of the
ecliptic, and of an irregular form, extending along the horizon. The
time was 4 A.M., and consequently was not due to any crepuscular light.
An explanation of the general fact of the brightest light being _always_
on the north side, is given in the present section, in connection with
another phenomenon. If, as some suppose, the light does not reach to the
sun, the annulus must at least fill all the space between Venus and the
earth, but it is far more in accordance with facts as well as with our
theory, to suppose it increases in density to the body of the sun.
Observations made at the observatory of the British Association,
detected, in 1850, sudden brightenings of the light, altogether
different from pulsations. The theory would refer these to that fitful
irregularity in the momentary intensity of the radial stream, which
gives the flickering and tremulous motion to comets' tails. But, the
steady variations in the intensity of this light must be due to other
causes. The longitude of the sun will here come in as a modifying cause;
for the obstruction caused by the body of the sun, when displaced from
the axis of the vortex, must necessarily exercise an influence on the
force and direction of the radial stream. A sudden influx of cometary
matter down the poles of the vortex, in more than usual quantities, will
also tend to brighten and enlarge the zodial light; and, in this last
cause, we have an explanation not only of ancient obscurations of the
solar light, but, also, of those phosphorescent mists, such as occurred
in 1743 and 1831, rendering moonless nights so light that the smallest
print could be read at midnight.
In total eclipses of the sun, the denser portion of the zodial light is
visible as a brilliant corona; but, on such occasions, the brightest
stars only are to be seen, and, consequently, the fainter portions of
the light must be invisible. Hind mentions as many as ten stars visible
in the total eclipse of 1842. According to the same authority, the color
of the corona was like tarnished silver, and rays of light diverged in
every direction, and appeared shining through the light of the corona in
the total eclipse of 1851. In this year on the day of the eclipse (July
28th), the longitude of the sun was about 340d, and, therefore, the body
of the sun obstructed the radial stream as seen from the earth on the
right side; but, in 1842, the longitude of the sun was, according to our
table, about 116d, the sun's centre then being 700,000 miles from the
axis of the vortex, and on the opposite side with respect to the earth;
the position was, therefore, not so favorable for the appearance of
these rays which, in many cases, have given the appearance of a whirling
motion to the corona.
At this date, July 7th, 1842, the corona, according to Prof. Airy,
"possibly had a somewhat radial appearance, but not sufficiently marked
to interfere with the general annular structure." Mr. Baily, on the
contrary, says, the corona had the appearance of brilliant rays; and, at
Milan, long jets of light were particularly noticed. There can be no
doubt but that the passage of the radial stream past the outer margin of
the moon must also give rise to the same phenomena as when passing the
sun, and in this we have an explanation of the fact, that, previous to
the moment of first contact, an appearance resembling a
faintly-illuminated limb of the moon, has been perceived near the body
of the sun; as well as of those flashes of light which have been
observed in the lunar disc as the eclipse advances. One important fact,
worthy of note, is, that these luminous streaks are more nearly parallel
than is due to a radiation from the centre. These streaks have, also,
been seen bent at right angles at the middle of their height, as a flame
is by means of a blowpipe, precisely analogous to cometary rays being
driven backwards to form the tail, as already described, thus indicating
a common origin. If the moon had an atmosphere, we should, no doubt, see
a greater display; but, having no rotating vortex to protect her from
the radial stream, her atmosphere must have been long since stripped
off, leaving her exposed to the withering winter blast of the great
stream of the solar vortex. In this connection, we may also allude to
the appearance of the moon when totally eclipsed. Instead of
disappearing at these times, she sometimes shines bright enough to
reveal her smallest spots. This has been generally referred to the
refraction of the earth's atmosphere bending inwards the solar rays. May
it not be owing to the brilliancy of the solar corona, which, in 1842,
was described as so intense that the eye was scarcely able to support
it? This is a far more palpable cause for the production of this
phenomenon, but of which astronomers cannot avail themselves, as long as
they are uncertain of the origin of this corona.