The English mathematical astronomer John Couch Adams (1819-1892) was a principal figure in the discovery of the planet Neptune.

Born at Laneast, Cornwall, on June 5, 1819, to a farm family of modest station, John Couch Adams early demonstrated a remarkable capacity for mathematics. He was admitted to Cambridge University on a scholarship in the fall of 1839, and when he graduated in 1843 he was appointed to the faculty, spending virtually the rest of his life there.

The chain of events in which Adams figured so prominently began long before his birth. In 1781 William Herschel had discovered the planet Uranus. From then on, astronomers had sought to account for the movement of Uranus according to the rules which governed the motions of the other planets. By Adams's day it was apparent that their attempts had failed. Although a new orbit had been computed as late as 1820, the refractory planet was already departing from its predicted path by about 1 minute of arc. Although such a small angle is almost inconceivable by the layperson (it is the angle subtended by a nickel at a distance of 100 yards), it represented an intolerable error for 19th-century astronomy.

Finding the Unknown Planet, Neptune

Adams's initial attack on Uranus, begun upon his graduation in 1843, lasted 2 1/2 years. Like earlier efforts, it was based on the law of universal gravitation, according to which the planet describes an essentially elliptical orbit around the sun with slight deviations caused by the attractions of other planets. Adams premised his work on the assumption that the computations of previous mathematicians had been spoiled by an unknown planet, whose actions on Uranus they necessarily failed to take into account. In September 1845 he presented his result to the director of the Cambridge observatory, indicating the approximate spot in the sky where the unknown planet should be found.

So unprecedented was Adams's prediction that no one knew how to treat it. Not until June 1846, when U.J.J. Leverrier in France published a similar result, did the English decide to drop their observational commitments and undertake the extensive search program to locate the planet. As was to appear later, they actually charted the planet on August 4 and 12 among the thousands of observations made. Before they could analyze all the data, however, the planet was discovered at Berlin on September 23 from the computations of Leverrier. Although Adams officially lost the honor of the discovery, the merit of his work was recognized, and his scientific reputation was established.

During the remaining 45 years of his life, he made important contributions to celestial mechanics and received many honors. He died in Cambridge on Jan. 21, 1892.

Further Reading

• Adams's professional work is republished in The Scientific Papers of John Couch Adams (2 vols., 1896-1900). There is no biography. Two accounts of Adams's greatest achievement are Sir Harold Spencer Jones, John Couch Adams and the Discovery of Neptune (1947), and Morton Grosser's highly readable The Discovery of Neptune (1962).