"The year 1846 will ever be memorable for having witnessed one of the most striking illustrations of the truth of Astronomy. Few can have forgotten the astonishment with which the discovery of the planet Neptune was then received, or the fact that it was due _not_ to a lucky or accidental pointing of the telescope toward a particular quarter of the heavens, but to positive calculations worked out in the closet; thus proving that before the planet was seen by the eye, it had already been grasped by the mind. The theory of its finding was a triumph of human intellect. The distant Uranus--a planet hitherto orderly and correct--begins to show unusual movements in its orbit. It is, somehow, not exactly in the spot where, according to the best calculations, it ought to have been, and the whole astronomical world is thrown into perplexity. Two mathematicians, as yet but little known to fame, living far apart in different countries, and acting independently of each other, concentrate the force of their penetrating intellects to find out the cause. The most obvious way of accounting for the event, was to have inferred that some error in previous computations had occurred; and in a matter so difficult, so abstruse, and so far off, what could have been more probable or more pardonable? But these astronomers knew that the laws of gravity were fixed and sure, and that figures truly based on them could not deceive. By profound calculations, each arrives at the conclusion that nothing can account for the "perturbation" except the disturbing influence of some hitherto unknown mass of matter, exerting its attraction in a certain quarter of the Heavens. So implicit, so undoubting is the faith of the French astronomer Leverrier, in the truth of his deductions, that he requests a brother astronomer in Berlin, Prussia, to look out for this mass at a special point in space, on a particular night; and there, sure enough, the disturber immediately discloses himself, and soon shows his title to be admitted into the steady and orderly rank of his fellow-planets. The coincidence of the two astronomers--Leverrier, of France, and Adams, of England, arriving at this discovery through scientific calculations, based upon knowledge derived from physical observation, precludes every idea of guess-work, while such was the agreement between their final deductions, that the point of the Heavens fixed upon by both as the spot where the disturber lay, was almost identical." "Such a discovery" says Arago, "is one of the most brilliant manifestations of the exactitude of the system of modern astronomy."