THE STORY OF NEPTUNE.
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!