An erroneous guess, if it is a good guess, sometimes produces excellent results. In 1778, Bode, of Berlin, published a “law” that states the distances of the various planets from the sun. It is often expressed simply in this way: Set down 4, and add to it successively the numbers 3, 6, 12, 24, etc., and the sums obtained, viz., 4, 7, 10, 16, 28, etc., represent the relative distances of all the planets from the sun, viz., Mercury 4, Venus 7, Earth 10, Mars 16, [Asteroids 28], Jupiter 52, etc. In reference to all the planets then known to exist, the correspondence of the alleged law to the facts was remarkable. The one point in which the alleged system utterly failed was in requiring the existence of a planet to fill the gap between Mars and Jupiter. So boldly did Biela press his convictions of the correctness of this law upon the notice of his fellow-workers, that they resolved, in 1800, to divide the zodiac into twenty-four zones, to be apportioned among them, for the express purpose of searching for undiscovered planets. This well-organized effort was, erelong, rewarded by the surprising discovery of four new planets, the first one on the first night of the new century, January 1, 1801, and three more soon after. As no more seemed to be forthcoming, the search was relinquished in 1816. A fifth was found in 1845, and nearly five hundred since. Since 1891 photography has been wondrously serviceable in finding these bodies. A sensitive plate, on being exposed toward that part of the sky which it is desired to examine, will record all the perceptible stars as round disks; while any planets that appear in the field of view will, by their motion, leave their trace in the form of elongated trails or streaks, thus betraying themselves at once on the photographs. In this way Charlois, of Nice, Italy, has found nearly ninety small planets. All these planetoids, as the minor planets are often termed, are quite small, being but twenty to one hundred miles in diameter, and not consequential members of the solar system. Bode’s law thus fulfilled its temporary mission; but egregiously failed when Neptune claimed admission to a place in the solar system, for its distance from the sun was utterly out of harmony with that required by the law of Bode.
III. HOW NEPTUNE WAS FOUND.
The patience of Job had a strong parallel in the labors of those tireless toilers to whose minute computations we owe our knowledge of Neptune’s path in the skies. For this far-off planet was discovered not by the use of a telescope, or any optical instrument, but simply by a process of mathematical reasoning. The story is simply this. For sixty years after Uranus was recognized, there were irregularities in its motion that could not be satisfactorily accounted for. In the orbit that it was believed to pursue, it was sometimes in advance of its proper position, and sometimes it seemed to fall behind. Sometimes it appeared to be drawn a little to the right, and at other times as far the other way.
The thought at last came separately to several penetrating minds, not that the observations of its position were in error, but that Uranus must be drawn away from its supposed path by the attraction exercised upon it by some unseen body. And if such an object existed, was it a planet? Where was it? How large was it? What was its path in the far-off ether?
THE MOVEMENT OF URANUS AND NEPTUNE.
The inner circle shows the position of Uranus at various dates; the outer circle the position of Neptune. The arrows show the direction toward which Uranus was drawn.
In the year 1842, the Royal Society of Sciences of Göttingen proposed as a prize question the full discussion of the theory of the motions of Uranus. It was specially sought to learn the cause of the large and increasing error of Bouvard’s Tables that had been relied upon to show its motion and its precise position at any time. Several able mathematicians undertook this intricate problem. Among them were John C. Adams, of Cambridge University, England, Sears C. Walker, of Washington, a man whose sad fate it was to pass away ere his magnificent abilities could receive extended recognition, and M. Le Verrier, of Paris. Working unknown to each other, they reached similar conclusions almost at the same time. Though not the first to solve the problem, the brilliant Frenchman was the first to announce his result, which he did by writing a letter to Dr. Galle, of the Berlin Observatory, where there was one of the largest telescopes in Europe, and asking him to search for his computed planet, and assigning its supposed place in the heavens. The very night he received the letter Dr. Galle found the planet within one degree of the point designated. The next night it had moved one minute of space, and was also seen to have a perceptible disk. This settled the question, and stamped it as a planet. Le Verrier well merited the title bestowed upon him, “First astronomer of the age.”