God of the sea; sign [Symbol], his trident.
DISTANCE FROM THE SUN, 2,775,000,000 MILES. DIAMETER, 34,500 MILES.
VELOCITY PER MINUTE, 201.6 MILES. AXIAL REVOLUTION UNKNOWN. ORBITAL,
164.78 YEARS. ONE MOON.
Men sought for Neptune as the heroes sought the golden fleece.
The place of Uranus had been mapped for nearly one hundred years
by these accidental observations. On applying the law of universal
gravitation, a slight discrepancy was found between its computed
place and its observed place. This discrepancy was exceedingly
slight. In 1830 it was only 20"; in 1840,190"; in 1884, 2'. Two
stars that were 2' apart would appear as one to the keenest unaided
eye, but such an error must not exist in astronomy. Years of work
were given to its correction. Mr. John C. Adams, of Cambridge,
England, finding that the attraction of a planet exterior to Uranus
would account for its irregularities, computed the place of such
a hypothetical body with singular exactness in October, 1841; but
neither he nor the royal astronomer Airy looked for it. Another
opportunity for immortality was heedlessly neglected. Meanwhile,
M. Leverrier, of Paris, was working at the same problem. In the
summer of 1846 Leverrier announced the place of the exterior planet.
The conclusion was in striking coincidence with that of Mr. [Page
176] Clark. Mr. Challis commenced to search for the planet near the
indicated place, and actually saw and mapped the star August 4th,
1846, but did not recognize its planetary character. Dr. Galle, of
Berlin, on the 23d of September, 1846, found an object with a
planetary disk not plotted on the map of stars. It was the
sought-for world. It would seem easy to find a world seventy-six
times as large as the earth, and easy to recognize it when seen. The
fact that it could be discovered only by such care conveys an
overwhelming idea of the distance where it moves.
[Illustration: Fig. 66.--Perturbation of Uranus.]
The effect of these perturbations by an exterior planet is understood
from Fig. 66. Uranus and Neptune were in conjunction, as shown,
in 1822. But in 1820 it had been found that Uranus was too far
from the sun, and too much accelerated. Since 1800, Neptune, in
his orbit from F to E, had been hastening Uranus in his orbit D
from C to B, and also drawing it farther from the sun. After 1822,
Neptune, in passing from E to D, had been retarding Uranus in his
orbit from B to A.
We have seen it is easy to miss immortality. There is still another
instance. Lalande saw Neptune on May 8th and 10th, 1795, noted that
it had moved a little, and that the observations did not agree;
but, supposing the first was wrong, carelessly missed the glory
of once more doubling the bounds of the empire of the sun.
[Page 177]
It is time to pause and review our knowledge of this system. The
first view reveals a moon and earth endowed with a force of inertia
going on in space in straight lines; but an invisible elastic cord of
attraction holds them together, just counterbalancing this tendency
to fly apart, and hence they circle round their centre of gravity.
The revolving earth turns every part of its surface to the moon in
each twenty-four hours. By an axial revolution in the same time
that the moon goes round the earth, the moon holds the same point
of its surface constantly toward the earth. If we were to add one,
two, four, eight moons at appropriate distances, the result would
be the same. There is, however, another attractive influence--that
of the sun. The sun attracts both earth and moon, but their nearer
affection for each other keeps them from going apart. They both,
revolving on their axes and around their centre of gravity, sweep
in a vastly wider curve around the sun. Add as many moons as has
Jupiter or Saturn, the result is the same--an orderly carrying
of worlds through space.
There lies the unsupported sun in the centre, nearer to infinity
in all its capacities and intensities of force than our minds can
measure, filling the whole dome to where the stars are set with
light, heat, and power. It holds five small worlds--Vulcan, Mercury,
Venus, Earth, and Mars--within a space whose radius it would require
a locomotive half a thousand years to traverse. It next holds some
indeterminate number of asteroids, and the great Jupiter, equal in
volume to 13,000 earths. It holds Saturn, Uranus, and Neptune, and
all their variously related satellites and rings. The two thoughts
that overwhelm us are distance and power. The period of [Page 178]
man's whole history is not sufficient for an express train to
traverse half the distance to Neptune. Thought wearies and fails in
seeking to grasp such distances; it can scarcely comprehend one
million miles, and here are thousands of them. Even the wings of
imagination grow weary and droop. When we stand on that outermost of
planets, the very last sentinel of the outposts of the king, the
very sun grown dim and small in the distance, we have taken only one
step of the infinite distance to the stars. They have not changed
their relative position--they have not grown brighter by our
approach. Neptune carries us round a vast circle about the centre of
the dome of stars, but we seem no nearer its sides. In visiting
planets, we have been only visiting next-door neighbors in the
streets of a seaport town. We know that there are similar neighbors
about Sirius and Arcturus, but a vast sea rolls between. As we said,
we stand with the outermost sentinel; but into the great void beyond
the king of day sends his comets as scouts, and they fly thousands
of years without for one instant missing the steady grasp of the
power of the sun. It is nearer almightiness than we are able to
think.
If we cannot solve the problems of the present existence of worlds,
how little can we expect to fathom the unsoundable depths of their
creation and development through ages measureless to man! Yet the
very difficulty provokes the most ambitious thought. We toil at
the problem because it has been hitherto unsolvable. Every error
we make, and discover to be such, helps toward the final solution.
Every earnest thinker who climbs the shining worlds as steps to
a higher thought is trying to solve the problem God has given us
to do.
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IX.