In 1840 the distinguished astronomer Bessel declared that attempts to explain the discrepancies "must be based on the endeavor to discover an orbit and a mass for some unknown planet, of such a nature, that the resulting perturbations of Uranus may reconcile the present want of harmony in the observations." Two years later he undertook researches in reference to the new planet of whose existence he felt certain. His labors, however, were interrupted by the death of his assistant Flemming, and by his own illness, which proved fatal in 1846, a few months before the actual discovery of Neptune. It is evident that the quest of the new planet had become general. The error of Uranus still amounted to less than two minutes. This deviation from the computed place is not appreciable by the naked eye, yet it was felt, by the scientific world, to challenge the validity of the Newtonian theory, or to foreshadow the addition of still another planet to our solar system. In July, 1841, John Couch Adams, a young undergraduate of St. John's College, Cambridge, whose interest had been aroused by reading Airy's paper on the _Progress of Astronomy_, made note of his resolution to attempt, after completing his college course, the solution of the problem then forming in so many minds. After achieving the B.A. as senior wrangler at the beginning of 1843, Adams undertook to "find the most probable orbit and mass of the disturbing body which has acted on Uranus." The ordinary problem in planetary perturbations calls for the determination of the effect on a known orbit exerted by a body of known mass and motion. This was an inverse problem; the perturbation being given, it was required to find the position, mass, and orbit of the disturbing planet. The data were further equivocal in that the elements of the given planet Uranus were themselves in doubt; the unreliability of its planetary tables, in fact, being the occasion of the investigation now undertaken. That thirteen unknown quantities were involved indicates sufficiently the difficulty of the problem. Adams started with the assumptions, not improbable, that the orbit of the unknown planet was a circle, and that its distance from the sun was twice that of Uranus. This latter assumption was in accord with the so-called "Bode's Law," which taught that a simple numerical relationship exists between the planetary distances (4, 7, 10, 16, 28, 52, 100, 196), and that the planets as they lie more remote from the sun tend to be more nearly double the distance of the next preceding. Adams was encouraged, by his first attempt, to undertake a more precise determination.