Some astronomers have given and are still giving their almost undivided attention to asteroidal investigation. The discoveries have been mostly made by a few principal explorers. The astronomer, Palisa, from the observatory of Pola and that of Vienna, has found no fewer than seventy-five of the whole group. The observer, Peters, at Clinton, New York, has found forty-eight asteroids; Luther, of Düsseldorf, twenty-four; Watson, of Ann Arbor, twenty-two; Borrelly, of Marseilles, fifteen; Goldschmidt, of Paris, fourteen, and Charlois, of Nice, fourteen. The English astronomers have found only a few. Among such, Hind of London, who has-discovered ten asteroids, is the leader.
The Italian, German and American astronomers are first in the interest and success which they have shown in this branch of sky-lore. Their investigations have made us acquainted with the dim group of little worlds performing their unknown part in the vast space between the Warrior planet and Jove.
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?