The discovery of the planet Neptune by Dr. Galle on the twenty-third
of September, 1846, was one of the most important events in the
intellectual history of this century. Certainly it was no small thing
to find a new world. Discoverers on the surface of our globe are
immortalized by finding new lands in unknown regions. What, therefore,
should be the fame of him who finds a new world in the depths of
space? Perhaps the discoverer of an asteroid or planetary moon may
not claim, in the present advanced stage of human knowledge, to rank
among the flying evangels of history; but he who found the great
planet third in rank among the worlds of the solar system, a world
having a mass nearly seventeen times as great as that of our own, may
well be regarded as one of the immortals.
We have referred the discovery of Neptune to Dr. Johann Gottfried
Galle, the German astronomer and Professor of Natural Sciences at
Berlin. But this Dr. Galle was only the _eye_ with which the discovery
was made. He was a good eye; but the eye, however clear, is only an
organ of something greater than the eye, and that something in this
case consisted of two parts. The first part was Urbain Jean Joseph
Leverrier, the French astronomer, of the Paris Observatory. The other
part was Professor John Couch Adams, the astronomer of the University
at Cambridge, England. These two were the thinkers; that is, they
were, as it were, jointly the great mind of the age, of which Galle
was the eye.
In getting a clear notion of the discovery of Neptune, several other
personages are to be considered. One of these is the astronomer Alexis
Bouvart, of France, who was born in Haute Savoie, in 1767, and died
in June of 1843, three years before Neptune was found. Another
personage was his nephew, the astronomer E. Bouvart, and a third was
the noted Prussian, Friedrich Wilhelm Bessel, Director of the
Observatory at Königsberg, who was born in 1784, and died on the
seventeenth of March, 1846, only six months before the discovery of
our outer planet.
Still another character to be commemorated is the English astronomer
Professor James Challis, Plumian Professor and Director of the
Observatory at Cambridge, England. This contributor to the great event
was born in 1803, and died at Cambridge on the third of December,
1882. Still another, not to be disregarded, is Dr. T.J. Hussey, of
Hayes, England, whose mind seems to have been one of the first to
anticipate the existence of an ultra-Uranian planet. And still again,
the English astronomer royal, Sir G.B. Airy must be mentioned as a
contributor to the final result; but he is to be regarded rather as a
contributor by negation. The great actors in the thing done were
Leverrier, Adams and Galle. English authors contend strongly for
placing the names in this order: Adams, Leverrier and Galle.
Suffice it to say that when Uranus was discovered by the elder
Herschel in 1781, that world was supposed to be the outside planet of
our system. Hitherto the splendid Saturn had marked the uttermost
excursion of astronomical knowledge as it respected our solar group.
For about a quarter of a century after Herschel's discovery the world
rested upon it as a finality. The orbit of Uranus was thought to
circumscribe the whole. But in the meantime, observations of this
orbit led to the knowledge that it did not conform in all respects to
astronomical and mathematical conditions. The orbit showed
irregularities, disturbances, perturbations, that could not be
accounted for when all of the known mathematical calculations were
applied thereto. Uranus was seen to get out of his path. At times he
would lag a little, and then at other times appear to be accelerated.
Each year, when the earth would swing around on the Uranian side of
the sun, the observations were renewed, but always with the result
that the planet did not seem to conform perfectly to the conditions of
his orbit. What could be the cause of this seeming disregard of
mathematical laws?
Astronomers could not accept the supposition that there was any actual
violation of the known conditions of gravitation. Certainly Uranus was
following his orbit under the centripetal and centrifugal laws in the
same manner as the other planets. There must, therefore, be some
undiscovered disturbing cause. It had already been noted that in the
case of the infra-Uranian planets they were swayed somewhat from their
paths by the mutual influence of one upon the other. This was
noticeable in particular in the movements of Jupiter, Saturn and
Uranus. When Saturn, for instance, would be on the same side of the
sun with Jupiter, it might be noted that the latter was drawn outward
and the former inward from their prescribed curves. The perturbation
was greatest when the planets were nearest, together. In like manner
Uranus did obeisance to both his huge neighbors on the sun's side of
his orbit. He, too, veered toward them as he passed, and they in turn
recognized the courtesy by going out of their orbits as they passed.
What, therefore, should be said of the outswinging movement of Uranus
from his orbit in that part of his course where no disturbing
influence was known to exist? Certainly _something_ must be in that
quarter of space to occasion the perturbation. What was it?
It would appear that the elder Bouvart, the French astronomer referred
to above, was the first to suggest that the disturbances in the orbit
of Uranus, throwing that planet from his pathway outward, might be and
probably were to be explained by the presence in outer space of an
unknown ultra-Uranian planet. Bouvart prepared tables to show the
perturbations in question, and declared his opinion that they were
caused by an unknown planet beyond. No observer, however, undertook to
verify this suggestion or to disprove it. Nor did Bouvart go so far as
to indicate the particular part of the heavens which should be
explored in order to find the undiscovered world. His tables, however,
do show from the perturbations of the orbits of Jupiter, Saturn and
Uranus that the same are caused by the mutual influence of the planets
upon one another.
It seems to have remained for Dr. T.J. Hussey, of Hayes, England, to
suggest the actual discovery of the unknown planet by following the
clew of the disturbance produced by its presence in a certain field of
space. Dr. Hussey, in 1834, wrote to Sir George Biddell Airy,
astronomer royal at Greenwich, suggesting that the perturbation of the
orbit of Uranus might be used as the clew for the discovery of the
planet beyond. But Sir George was one of those safe, conservative
scholars who scorn to follow the suggestions of genius, preferring
rather to explore only what is known already. He said in answer that
he doubted if the irregularity in the Uranian orbit was in such a
state of demonstration as to give any hope of the discovery of the
disturbing cause. He doubted even that there was such irregularity in
the Uranian orbit. He was of opinion that the observers had been
mistaken in the alleged detection of perturbations. So the Greenwich
observatory was not used on the line of exploration suggested by
Hussey.
Three years afterward, and again in 1842, Sir George received letters
from the younger Bouvart, again suggesting the possibility and
probability of discovering the ultra-Uranian planet. These hints were
strengthened by a letter from Bessel, of Königsberg. But Sir George B.
Airy refused to be led in the direction of so great a possibility.
It was in 1844 that Professor James Challis, of the Cambridge
observatory, appealed to Sir George for the privilege of using or
examining the recorded observations made at Greenwich of the movements
of Uranus, saying that he wished these tables for a young friend of
his, Mr. John C. Adams, of Cambridge, who had but recently taken his
degree in mathematics. Adams was at that date only twenty-five years
of age. The royal astronomer granted the request, and for about a year
Adams was engaged in making his calculations. These were completed,
and in September of 1845, Challis informed Sir George Airy that
according to the calculations of Adams the perturbations of Uranus
were due to the influence of an unknown planet beyond.
The young mathematician indicated in his conclusions at what point in
the heavens the ultra-Uranian world was then traveling, and where it
might be found. But even these mathematical demonstrations did not
suffice to influence Sir George in his opinions. He was an Englishman!
He refused or neglected to take the necessary steps either to verify
or to disprove the conclusions of Adams. He held in hand the
mathematical computations of that genius from October of 1845 to June
of the following year, when the astronomer Leverrier, of Paris,
published to the world his own tables of computation, proving that the
disturbances in the orbit of Uranus were due to the influence of a
planet beyond, and indicating the place where it might be found. There
was a close agreement between the point indicated by him and that
already designated by Adams.
It seems that this French publication at last aroused Sir George Airy,
who now admitted that the calculations of Adams might be correct in
form and deduction. He accordingly sent word to Professor Challis to
begin a search for the unknown orb. The latter did begin the work of
exploration, and presently saw the planet. But he failed to recognize
it! There it was; but the observer passed it over as a fixed star. As
for Leverrier, he sent his calculations to Dr. Galle, of Berlin; and
that great observer began his search. On the night of the twenty-third
of September, 1846, he not only _saw_ but _caught_ the far-off world.
There it was, disc and all; and a few additional observations
confirmed the discovery.
Hereupon Sir George Airy broke out with a claim that the discovery
belonged to Adams. He was able to show that Adams had anticipated
Leverrier by a few months in his calculations; but the French scholars
were able to carry the day by showing that Adams' work had been void
of results. The world went with the French claim. Adams was left to
enjoy the fame of merit among the learned classes, but the great
public fixed upon Leverrier as the genius who did the work, and Dr.
Galle as his eye.
Several remarkable things followed in the train. It was soon
discovered that both Leverrier and Adams had been favored by chance in
indicating the field of space where Uranus was found. They had both
proceeded upon the principle expressed in Bode's Law. This law
indicated the place of Neptune as 38.8 times the distance of the earth
from the sun. A verification of the result showed that the new-found
planet was actually only thirty times as far as the earth from the
sun. In the case of all the other planets, their distances had been
remarkably co-incident with the results reached by Bode's Law; but
Uranus seemed to break that law, or at least to bend it to the point
of breaking--a result which has never to this day been explained.
It chanced, however, that at the time when the predictions of
Leverrier and Adams were sent, the one sent to Galle and the other to
Challis, Uranus and the earth and the sun were in such relations that
the departure of the orbit of Uranus from the place indicated by
Bode's Law did not seriously displace the planet from the position
which it should theoretically occupy. Thus, after a little searching,
Challis found the new world, and knew it not; Galle found it and knew
it, and tethered it to the planetary system, making it fast in the
recorded knowledge of mankind.
While Daniel O'Connell, the greatest Irishman of the present century,
despairing of the cause of his country, lay dying in Genoa, and while
Zachary Taylor, at the head of a handful of American soldiers was
cooping up the Mexican army in the old town of Monterey, a new world,
37,000 miles in diameter and seventeen times as great in mass as the
little world on which we dwell, was found slowly and sublimely making
its way around the well nigh inconceivable periphery of the solar
system!