THE PLANETS AND ASTEROIDS.
MERCURY.
Including our own globe there are eight principal planets—viz.,
Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. The two
first-named being between us and the sun, are termed _interior_
planets; the others are _exterior_. Mercury, Venus, and Mars are
smaller than Earth. The other four are much larger.
[Illustration: Fig. 576.—An Orrery.]
We have already described the planets as bodies wandering through the
zodiac, and reflecting the sun’s light. Their orbits are very different
from the moon’s; for instance, planets take a retrograde motion as
well as a direct one. The sun and the planets revolving around him
constitute the solar system.
We will commence our brief consideration of them with Mercury, the
planet nearest to the sun.
The distance of Mercury from the sun is 35,000,000 of miles, less than
half the distance our earth is from him, and so receives much more
heat and light than we do. The sun to the Mercurians, if there be any
inhabitants upon the planet, must appear about seven times larger than
he does to us. Mercury’s year is about eighty-five days in length,
so the seasons must be shorter if they follow the same rotation as
ours. It passes through space with an exceedingly rapid motion, and so
probably the ancients called the swift planet Mercury after the winged
messenger of Jove.
Mercury is not an easy planet to observe, owing to its proximity to the
sun, yet the ancients managed to descry it. But it can be seen just
before sunrise and sunset in autumn, and in spring if the weather be
clear. It possesses phases similar to our moon. Some authorities have
stated that Mercury has an atmosphere, but this circumstance, as well
as its formation, is still shrouded in mystery. Mercury’s day is a few
minutes longer than ours.
[Illustration: Fig. 577.—Transit of Mercury.]
A transit of Mercury is represented in the accompanying illustration
(fig. 577). This phenomenon took place in 1845, but there have been
many others noticed. The first recorded took place in November 1631,
and these transits always occur in May or November.
VENUS.
Venus is the planet next in order, and revolves about 66,000,000
of miles from the sun. It is the nearest planet to the earth, and
is somewhat smaller than the latter. This planet is both a morning
and evening star, and is very brilliant—so much so, that any close
observation with the telescope is not possible; and when at her nearest
point she is invisible as she passes between us and the sun, and of
course when fully illuminated she is directly beyond the sun, and
enclosed in his rays. But under other circumstances she is distinctly
visible as a crescent in the evening, and nearly full as a morning
star. Venus goes round the sun in 224 days, and her day is rather less
than ours.
[Illustration: Fig. 578.—Orbit of Venus.]
Venus has long been celebrated as the morning and evening star, as
“Lucifer” and “Hesperus.” “Lucifer, son of the morning,” is mentioned
by Isaiah. That Venus possesses an atmosphere denser than our own
can scarcely be doubted. The observations made during the successive
transits, particularly the last (1874), seem to have established the
fact that aqueous vapour exists around, and water in, Venus. No
satellite can be found, though the ancients reported such an attendant
upon this planet.
The apparent diameter of Venus varies considerably in consequence of
her varying distances at the inferior and superior conjunction. When
nearest the earth, if she presented her fully illuminated disc to our
gaze, we should see a miniature moon, and even under the circumstances
Venus throws a shadow, so brilliant is her light.
[Illustration: Fig. 579.—Venus, at quadrature.]
The transits of Venus have been referred to, and, like those of
Mercury, are simply a passing, or “transit,” of the planet across the
illuminated disc of the sun. The transits afford means to ascertain
the volume and distance, etc., of the sun, and this year (1882) the
next transit is expected. There will not be another for more than one
hundred years.
[Illustration: Fig. 580.—Venus, near inferior conjunction.]
Whether Venus has a constitution similar to our globe is of course
doubtful. The matter is less dense than the earth, and there is an
atmosphere half as dense again as ours. Spots have been noticed
crossing the planet, which may have been vapours or clouds, and the
rotation of Venus on its axis was calculated from these spots as being
23^h 21^m 22^s. The seasons in Venus must be very different from ours,
as her inclination is greater than our earth, and as the sun is so much
nearer to her than to us her tropical and polar regions are close, and
a vertical sun is scarcely enjoyed by two places for three successive
days, and she may have two winters and summers, two springs and autumns!
MARS.
Having already considered the earth, we pass on from Venus to Mars. The
orbit of the latter planet is exterior to the earth’s, as is proved by
his never appearing “horned,” nor ever passing across the sun’s disc.
Therefore no “transits” of Mars can take place as transits of Venus and
Mercury.
Yet Mars is most favourably situated for astronomical observation by
us, because it turns its full disc to us. Venus is nearer to us than
Mars—but, as we have explained, when she comes nearest to us she is
quite invisible. Astronomers have been enabled to ascertain a good deal
concerning the planet of war—“the red planet Mars.”
Mars has been considered very like the earth. We perceive seas and
continents, and the shape of Mars is like the earth. But our globe is
larger than Mars, which is much less dense, so the force of gravitation
is less also. Mars moves upon his axis in about twenty-four hours
and a half, and takes rather more than 686 days to revolve round the
sun. (_See_ page 489.) Thus its days are a little longer than, and its
years twice as long as our days and years. When in “opposition,” or on
the opposite side of us from the sun, Mars is at his brightest. This
happened in September 1877. He will come close again to us in 1892.
[Illustration: Fig. 581.—Mars seen from the earth.]
All planets are wanderers, but of all the wanderers Mars has the most
eccentric orbit. He curls about, so to speak, in loops and curves in
a very irregular manner, and therefore his distance from the earth
varies very considerably; and this eccentric behaviour of the warlike
planet must have, as we believe it did, puzzled the ancients very
much. But—and here reason came to human aid—this very fact, this great
eccentricity of the planetary motions, caused Copernicus to investigate
the subject with great attention, and he at length explained the true
reason of these irregular orbits from the hypothesis that it was around
the sun, and not around the earth that the planets moved in regular
orbits.
It is quite ascertained that Mars is very like our earth in miniature.
We annex a diagram of the planet, and when it is examined with a good
telescope the seas and continents can be quite distinctly perceived.
At the poles there appears to be a white or snowy region at varying
periods, which would lead us to the conclusion that the atmospheric
changes and the seasons are similar to our own; and as the inclination
of the planet is nearly the same as the earth, this supposition may be
accepted as a fact.
Thus we see that Mars is the most like earth of all the planets, and
its inhabitants—if, indeed, it is now inhabited—must have a beautiful
view of us when the weather is fine, for we are so much larger. Mars is
also attended by two satellites, or moons, as Professor Hall reported
from Washington in 1877. These moons have been named _Deimos_ and
_Phobos_, and are both very small, their diameter being only about six
miles; but late astronomers have reasoned that they must be three times
this diameter.
[Illustration: Fig. 582.—Earth seen from Mars.]
There have been numerous theories concerning Mars being inhabited, and
of course these suggestions made respecting life on one planet may,
with varying circumstances, be applied to another. Each planet may
have had, or may yet have, to pass through what has been termed a
“life-bearing stage.” We on earth are at present in the enjoyment of
that stage. So far as we can tell, therefore, Mars may be inhabited
now, as he bears much the same appearance as our planet. Certain
changes are going on in Mars, and all planets, just as they go on here
in our earth, and as they did long, long ages before the earth was
populated, and which will continue to go on after life on the earth has
ceased to exist.
Mars is, as we know, much further away from the sun than earth is, and
must receive less direct heat. When he was created, or formed, we can
only conjecture, but in all probability he cooled before the earth did,
as he is smaller. Here another theory concerning the state of Mars
arises, and in support of it we may quote an American authority upon
the planet.
“His mass is not much more than one-ninth of the earth’s, while his
surface is about one-third of hers. Then, if originally formed of
the same temperature, he had only one-ninth her amount of heat to
distribute. If he had radiated it away at one-ninth of her rate, his
supply would have lasted as long, but radiation takes place from the
surface in proportion to the surface, hence he parted with it three
times as fast as he should have done to cool at the same rate as the
earth, and must have attained a condition which she will not attain
until three times as long an interval has elapsed from the era of her
first existence than has already elapsed. Geologists agree that the
last-named period must be measured by many millions of years; hence it
follows that twice as many millions of years must elapse before our
earth will be in the same condition as Mars, and Mars must be three
times as far on the way toward planetary decrepitude and death as
our earth. Then assigning two hundred thousand years as the extreme
duration of the period during which men capable of studying the
problems of the universe have existed, and will exist on this earth,
the theory holds that Mars would have entered on that stage of his
existence many millions of years ago, and that the appearance of the
planet itself implies a much later stage of planetary existence.”
Mars is a very interesting study, and the reddish hue which is so
distinctive is perceived in certain spots when examined by the
telescope’s aid. These red places were discovered by Cassini. Mr. Dawes
made drawings of Mars, and Mr. Proctor has by their aid constructed a
regular map of Mars, and a chart of the surface of the planet. There
is much more land than water on Mars, as the bright surfaces which
indicate land are much more extensive than the darker portions which
betoken the existence of water. But these “markings” are not always
visible, in consequence of something coming between us and the land on
Mars, and this has been attributed to the production of vegetation,
which a French _savant_ declared was ruddy-coloured, and that this
autumnal tint departed in the winter.
The seasons of Mars are not equal, in consequence of his wandering
propensities, and winter is warmer up there than our winter, while
summer is cooler than our summer. That there are clouds and an aqueous
atmosphere surrounding Mars we learn from spectroscopic observation
and analysis, and in fine we may look upon Mars as similar to our
earth. Respecting the question of its habitation we take the liberty to
quote Mr. Richard Proctor:—
“I fear my own conclusion about Mars is that his present condition is
very desolate. I look on the ruddiness of tint to which I have referred
as one of the signs that the planet of war has long since passed its
prime. There are lands and seas in Mars, the vapour of water is present
in his air, clouds form, rains and snows fall upon his surface, and
doubtless brooks and rivers irrigate his soil, and carry down the
moisture collected on his wide continents to the seas whence the clouds
had originally been formed. But I do not think there is much vegetation
on Mars, or that many living creatures of the higher types of Martian
life as it once existed still remain. All that is known about the
planet tends to show that the time when it attained that stage of
planetary existence through which our earth is now passing must be
set millions of years, perhaps hundreds of millions of years ago. He
has not yet, indeed, reached that airless and waterless condition,
that extremity of internal cold, or in fact that utter unfitness to
support any kind of life, which would seem to prevail in the moon. The
planet of war in some respects resembles a desolate battle-field, and
I fancy that there is not a single region of the earth now inhabited
by man which is not infinitely more comfortable as an abode of life
than the most favoured regions of Mars at the present time would be for
creatures like ourselves.”
[Illustration: Fig. 583.—CHART OF MARS (Names according to Proctor and
Green).
A Peer Continent.
B Herschel Continent.
C Fontana Land.
D Secchi Continent, East.
E Secchi Continent, Central.
F Secchi Continent, West.
G Mädler Continent.
H Leverrier Land.
1 Herschel Strait.
2 Dawes Ocean.
3 Maraldi Sea.
4 Oudemans Sea.
5 Trouvelot Bay.
6 Funchal Bay.
7 Campani Sea.
8 De la Rue Ocean.]
THE MOONS OF MARS.
We must devote a few lines to the satellites of Mars, which during
the last four years have proved a very interesting study for the
astronomers, and some very interesting facts have been ascertained
concerning the ruddy planet, which is now proved not to be “moonless
Mars,” as the poet declared.
There are two satellites, which, in consequence of their distance
from him, being so different, vary in apparent size. The outer one is
twelve thousand, the inner one about three thousand five hundred miles
from the planet, so the former would revolve in about thirty hours in
a direction from west to east, and the inner moon goes round in the
same way in about seven hours and a half. Mars revolves in twenty-four
and a half hours from west to east. So the outer moon rises for him in
the east, and the inner one in the west. This is accounted for by the
fact that one travelling slower than Mars rises in the east, the other
outruns him, and comes up in the west.
But if we suppose ourselves upon Mars we shall find that, after all,
we have only one moon properly so called. The outer satellite is very
small and very far away, so it is useless to give light—at most, it
is no bigger than Mars appears to us on earth. So the Martians do not
see two moons passing each other in the sky—that is, unless their eyes
are of greater range and power than ours. Thus they have one moon
rising in the west, appearing in all its phases _every night_, while
our moon takes twenty-eight days to pass through her phases; for we
must remember that Mars’ moon takes only seven hours and forty minutes
to pass through its orbit, and therefore each quarter will not occupy
quite two hours.
THE MINOR PLANETS, OR ASTEROIDS.
Passing onward from Mars towards Jupiter we arrive at a number of
smaller planets, which will not concern us very much, as they are
very small and scarcely visible without a good telescope. But a very
interesting chapter in the history of astronomy was commenced when the
discovery of these bodies was begun. In old times astronomers noticed
a very considerable gap between Mars and Jupiter, which was remarkable
when the regular progression of the distances between the planets
was remembered. So Kepler was of opinion that some planet would be
discovered having its orbit in that space between Mars and Jupiter. It
is, however, to Piazzi, the Italian, that the discovery of the zone of
asteroids is due.
[Illustration: Dec. 8th. Dec. 9th.
Fig. 584.—Field of view showing motion of minor planets amongst the
stars.]
Piazzi was surveying the constellation Taurus, where he fancied he had
discovered a change of place in a star which he had observed on the
1st of January in that year (1801). He was quite sure of this change
next day (the 3rd of January), and he expressed his opinion to Bode and
Oriani. But letters took a long time to pass in those days, and when
the other astronomers had received the advices the new star had been
lost in the sun’s glory. But after a year, on the 31st December, 1801,
the planet was again seen and the discovery was proved. The new planet
was named CERES.
The discovery of Ceres led to other discoveries. For, while searching
for her, Olbers found other minor planets, and so on to the present
day. Now we have nearly two hundred asteroids, and more are probably to
be found in the zone beyond Mars.
It would answer no purpose to give a list of the asteroids. We need
only remark that the first four were discovered in quick succession,
and then a lapse of thirty-eight years occurred before the fifth was
found, thus—
CERES, discovered by Piazzi at Palermo, January 1st, 1801.
PALLAS, “ Olbers at Bremen, March 28th, 1802.
JUNO, “ Harding at Lillienthal, September 2nd, 1804.
VESTA, “ Olbers at Bremen, March 20th, 1807.
ASTRÆA, “ Hencke at Driessen, December 8th, 1845.
Since 1848 there have been numerous minor planets discovered every year.
The hypothesis that all these asteroids are fragments of one large
planet which has been destroyed was started by Olbers; and in
confirmation of this view it has been determined that the asteroids
have essentially the same character. The orbits of these minor planets
are different from the larger “wanderers,” and cross each other, as
will be seen from the accompanying diagram, so that a collision may one
day ensue.
Planetoids and extra zodiacal planets are titles which have been
bestowed upon these bodies, of which VESTA is the first in order in the
system, and revolves in 1,325 days, at a mean distance of 225,000,000
of miles from the sun. JUNO and CERES take each about four of our years
to revolve in their orbits, at greater distances still, averaging
260,000,000 of miles. Pallas and Ceres are most alike in their periods
and distance from the sun; the principal asteroids are only about 300
miles in diameter, while the smaller are very tiny indeed, and one
certainly has quite disappeared.
[Illustration: Fig. 585.—Orbit of asteroids.]
JUPITER, THE GIANT.
Jupiter has been well named the Giant planet, since his diameter is
eleven times greater, and he is thirteen hundred times larger than our
planet. His inclination is very small, and you now know that under such
circumstances he enjoys very small changes of seasons. Jupiter has four
moons, or satellites, and an illustration of the “Jovian System” is
herewith given.
[Illustration: Fig. 586.—The Jovian System.]
Jupiter himself was well known to the ancients, but Galileo was the
discoverer of the “moons.” His telescope was, of course, a very
imperfect instrument, and while he was gazing at the planet he noticed
three stars close by the bright disc, two on one side, but next day
Galileo perceived them all at the same side. Next time he looked there
were only two, and after many anxious observations he found out, not
only that Jupiter had three attendant stars, but four!
These moons were found to revolve round Jupiter in times varying from
nearly two days to nearly sixteen days, according as they were at a
less or greater distance from him. They were found to have their times
of eclipses and transits, etc., also. These moons act with respect to
Jupiter very much as the inner planets act with respect to the sun, for
observation showed Galileo that the satellites sometimes appeared on
one side of the planet, and at other times on the opposite side.
From the diagram of the Jovian System we shall understand the orbits
of the moons, which are all of nearly equal size,—two thousand miles
in diameter,—and cause eclipses of the sun to Jupiter. If the earth
be in the same direction as the sun the moons are lost to view. The
satellites disappear into the shadow, and are eclipsed at 1′″, 2′″,
3′″, 4′″, respectively, but they do not always come into view again
immediately they have passed through the planet’s shadow, because the
earth is a little at one side of the sun. So when the satellite gets
behind the edge of Jupiter, his shadow being on the opposite side to
the satellite’s, it is said that the “moon” is in “occultation”; when
it disappears in the shadow it is “eclipsed.” Cassini discovered the
“transit” of Jupiter’s moons. The annexed diagram illustrates the
eclipses, etc., very clearly. At the four points, A B C D, we have the
earth; J is Jupiter with his moons; 1 2 3 4 is their orbits. At _a_
moon No. 1 enters his shadow, and emerges at _b_. From the earth at D
_a_ will be visible, but not _b_, because Jupiter is in the way. So at
B, the coming out, or _emersion_, will be visible, but not the entrance
into the shadow, or _immersion_. At A the satellite is in transit _d_,
on the disc of the planet, J.
[Illustration: Fig. 587.—Satellite in Transit.]
[Illustration: Fig. 588.—Eclipses of Jupiter’s Moons.]
From the observation of the eclipses of Jupiter’s moons the rate of
the transmission of light was discovered by Roëmer in 1675, and its
progressive motion was calculated. The eclipses were noticed to take
place later than the calculated time, when the planet was approaching
conjunction. Roëmer suggested that the delay was owing to the greater
distance the light had to travel—a distance equal to the diameter of
the earth’s orbit, or about 190,000,000 of miles. The time was about
sixteen minutes. Light was found to travel at the rate of nearly
12,000,000 of miles a minute.
Let us now endeavour to picture Jupiter himself. Here we have an
illustration of the planet. He is the biggest, and the brightest,
except Venus, of all the planets. He revolves at a distance of
476,000,000 of miles from the sun, and his year is equal to nearly
twelve of ours, while his day is scarcely ten hours long, showing
a rapidity more than twenty times the rate of our earth. Jupiter,
therefore, must have a very much greater diameter than the earth.
There is much less sunlight and heat found on Jupiter than upon Earth,
because he is so much farther from the sun than we are, but at the same
time the heat comes at less intervals than with us. And here the theory
already noticed respecting the gradual cooling of the planets will be
remembered. Jupiter, we can easily imagine, would take much longer to
get cool than Mars or the earth, and, though his rapid rotation would
assist him, he must be still in the midst of a glowing atmosphere
without form and void—perhaps a furnace for cloud and vapour generation.
[Illustration: Fig. 589.—Jupiter.]
Now when Jupiter is examined with the telescope it will be seen that
he is crossed by belts of vapour (_see_ also page 489); and when we
consider the results of the spectrum analysis of the planet, we may
fairly assume that Jupiter is in a very heated state, and that we
cannot really perceive the actual body of the planet at all yet. There
is an immense quantity of water thus surrounding Jupiter, and he is
still in the condition in which our earth was before geology grasps
its state, and long ere vegetation or life appeared. The waters have
yet to be “gathered together into one place,” and the dry land has yet
to appear upon Jupiter, who is a very juvenile, if a very enormous
planet. Under these conditions we can safely assume that there are no
inhabitants of Jupiter.
The belts, or zones, of Jupiter vary in hue, and the continual
changes which are taking place in this cloud region tend to show that
disturbances of great magnitude and importance are occurring.
It is useless to speculate upon what will happen in Jupiter when the
disc is eventually cooled. The planet, we know, has not nearly reached
maturity; the earth is in the full prime of its life, and the moon is
dead and deserted. What the millions of years which must elapse before
Jupiter has cooled may bring forth we need not try to find out. The
earth will then, in all probability, be as dreary as the moon is now,
and we shall have returned to dust.
SATURN.
We now come to the most curious of all the planets—Saturn, which is
an immense globe surrounded by a beautiful bright ring, or rather
series of rings, and attended by eight moons. He appears to possess
much the same constitution as Jupiter, but enveloped in an even denser
atmosphere than the latter. Saturn’s diameter is about nine times
greater than the earth; he revolves on an inclined axis in about ten
hours, and has seasonal alternations of unequal length. His year is
about thirty of ours (10,759 days). The most striking phenomena in
connection with Saturn are his _rings_.
[Illustration: Fig. 590.—Saturn.]
Saturn’s rings are supposed to be a close agglomeration of stars, or
satellites, revolving around the planet and encircling him in a belt.
The rings are apparently broad and flat and thin, resembling roughly
the horizon of a globe.
The globe of the planet is not exactly in the centre of the rings,
which have been measured, and are approximately as below:—
Diameter of exterior ring 169,000 miles.
Diameter of interior ring 124,000 “
Diameter of innermost ring 100,000 “
Interval between innermost ring and Saturn 19,000 “
Intervals between the rings 18,000 “
Thickness of the rings 130 “
Breadth of the rings 37,000 “
[Illustration: Fig. 591.—Saturn’s rings at Equinox.]
The rings were first recognised as such by Huyghens in 1659, but
Galileo had remarked the curious appearance the planet presented.
Cassini confirmed Huyghens’ discovery, and found that the ring was
duplicated, and Mr. Ball made the same discovery. The two outermost
rings are very bright, the inner ring being darker and partially
transparent, for the ball of Saturn can be perceived through it.
[Illustration: Fig. 592.—Enlarging ring.]
But the rings are not always so plainly seen as in the foregoing
diagram. Sometimes they appear as a mere line of light on each side
of the planet, as shown in the margin. This occurs at the time of the
equinox (fig. 591). By degrees, however, as they become inclined, they
appear broader (fig. 592). The inner ring may be formed of vapour, but
the outer ones are of something more solid, as the shadows they cast
upon the planet, and it casts upon them, at certain times (figs. 593
and 594).
[Illustration: Fig. 593.—Ring shadow.]
Saturn possesses eight moons, seven of them revolving in orbits on the
plane of the rings, but one is more inclined. These eight satellites
have been named as follows:—
+-------------+-------------------------+-------------+-----------------+
| Name. | Distance from Saturn in | Time of | Discoverer. |
| | radii of Saturn. Miles. | Revolution. | |
+-------------+-------------------------+-------------+-----------------+
| | | d. h. min. | |
| 1 Mimas | 3·36 (about) 120,000 | 22 37 | Herschel. |
| 2 Enceladus | 4·30 “ 150,000 | 1 8 53 | Herschel. |
| 3 Tethys | 5·34 “ 190,000 | 1 21 18 | Cassini. |
| 4 Dione | 6·84 “ 240,000 | 2 17 41 | Cassini. |
| 5 Rhea | 9·55 “ 340,000 | 4 12 25 | Cassini. |
| 6 Titan | 22·15 “ 790,000 | 15 22 41 | Huyghens. |
| 7 Hyperion | 26·78 “ 945,000 | 21 7 7 | Lassel and Bond.|
| 8 Iapetus | 64·36 “ 2,250,000 | 79 0 8 | Cassini. |
+-------------+-------------------------+-------------+-----------------+
But these eight moons are not so interesting as those belonging to
Jupiter, because the great distance they are away precludes much
examination of them. They vary much in size, Titan being the largest,
and perhaps equal to Mars, Iapetus being next in magnitude. The
light of these satellites and the rings is no doubt very great in
the aggregate, and must have a magnificent appearance in the heavens
(compare page 493). Very likely there are other attendants upon
Saturn, but owing to the brilliancy of the rings it is impossible to
distinguish them.
[Illustration: Fig. 594.—Ring shadow.]
URANUS.
Uranus was discovered by Herschel in 1781, and has been called after
its discoverer, and sometimes the “Georgium Sidus.” It revolves at an
enormous distance from the sun—viz., 1,753,000,000 of miles. It takes
about eighty-four of our years (30,686 days) to go round the sun, and
possesses four moons. It is very much larger than the earth—about four
times the diameter, and forty times its volume. We can only speculate
concerning its physical constitution, which is assumed to be similar
to that of Jupiter, while the changes of temperature and seasons must
vary immensely. The names of the moons are Ariel, Umbriel, Titania, and
Oberon. The outer pair can be seen without much difficulty.
NEPTUNE.
The existence of this planet was determined by calculation before it
had been seen at all. Uranus was observed to be disturbed in his orbit,
moving sometimes faster than at others; and even before Uranus had been
discovered Saturn and Jupiter had been seen to be affected by some
body in the system. M. Leverrier determined to ascertain the cause of
this, and came to the conclusion that some other planet was influencing
Uranus. The Newtonian theory here received a most convincing proof.
While Leverrier was calculating, Mr Adams of Cambridge leaped to the
same conclusion, and wrote the result of his calculations to Professor
Airy, and the planet was seen, but not reported upon. Meantime
Leverrier published his calculations, and the observers at Berlin
detected the new planet in September 1846.
[Illustration: Fig. 595.—Neptune in field of view with stars of 6th,
7th, 8th, and 9th magnitudes.]
Very little can be said concerning Neptune, as its distance is too
great for observation. It is at 2,746,000,000 of miles from the sun,
and takes 164 years to go round it (60,126 days). It is about the same
size as Uranus. It has one moon, which moves round the planet in 5^d
21^h, and is of great size.