and at the same time the more numerous modern ones; and it was finally concluded that the ancient observations were erroneous, or that some strange and unknown action disturbed, or had disturbed, the planet; consequently M. Bouvard discarded entirely the old observations, and used only those taken between 1781 and 1820, in constructing the tables of Uranus. For some years past it has been found that the tables thus constructed do not agree any better with modern observations, than they do with the ancient observations; _consequently it was evident that the planet was under the influence of some unknown cause_. Several hypotheses have been suggested as to the nature of this cause; some persons talked of a resisting medium; others of a great satellite which might accompany Uranus; some even went so far as to suppose that the vast distance Uranus is from the Sun caused the law of gravitation to lose some of its force; others thought that the rapid flight of a comet had disturbed its regular movements; others thought of the existence of a planet beyond Uranus, whose disturbing force caused the anomalous motions of the planet; but no one did otherwise than follow the bent of his inclination, and did not support his assertion by any positive considerations. “Thus was the theory of Uranus surrounded with difficulties, when M. Le Verrier, an eminent French mathematician, undertook to investigate the irregularities in its motions. His first paper appeared on the 10th November, 1845, and his second on June 1, 1846 (published in the Comptes Rendûs). In this second paper, after a most elaborate and careful investigation, he proves the utter incompatibility of any of the preceding hypotheses to account for the planet’s motions, except only that of the last one, viz., that of a new planet. He then successively proves that this planet cannot be situated either between the Sun and Saturn, or between Saturn and Uranus; but that it must be beyond Uranus. And in this paper he asks the following questions:--‘Is it possible that the irregularities of Uranus can be owing to the action of a planet situated in the ecliptic, at a distance of twice the mean distance of Uranus from the Sun? If so, where is it actually situated? What is its mass? What are the elements of the orbit it describes?”