Professional Career and Contributions
While at St. John's College as an undergraduate, John came across a problem that caught his attention. The planet Uranus had irregularities in its motion, which at the time could not be explained. John wanted to pursue the problem, and to him it seemed that the irregularities could be explained if one would assume the existence of another planet. John worked on the problem after graduating from St. John's and resolved it with an astounding solution. According to his calculations the irregularities were due to the existence of another planet beyond the orbit of Uranus.
John presented his solution to James Chalis, the director of the Cambridge Observatory, in 1845. Meanwhile, at about the same time, another astronomer by the name of Urbain Le Verrier was working on the same problem and came up with the same solution. He presented his solution independently to the French Academy of Sciences in 1845. Eventually, the new planet was named Neptune and the world recognized that both astronomers independently reached the solution and gave equal recognition to both.
This discovery gave John's carrier a huge boost and in 1847 he was offered knighthood by Queen Victoria. However, John modestly declined the honor. In the meantime he was working a fellowship at St. John's College. In 1848, the Royal Society awarded John its Copley Medal for his discovery. St. John's College founded an Adam's prize to be awarded to students on a breakthrough treatise in mathematics in the same year. In 1851, John was elected to the position of president of the Royal Astronomical Society and the following year his fellowship at the university came to an end. Pembroke College saw this as an opportunity to acquire him and elected him to a lay fellowship at the college, which John held the remainder of his life. He held a short position as professor of mathematics at St. Andrews and then was offered the position of Lowndean Professorship of Astronomy and Geometry at Cambridge. In 1860, he succeeded Challis as the director of the Cambridge Observatory. Here he remained till his death.
In 1852, John published astoundingly accurate tables on the Moon's parallax. The following year, John worked on the problem of the mean motion of the Moon relative to the stars, which had been previously established by La Place and had remained unchallenged for sixty years. His results displaces partially the long held theory of La Place and was met with skepticism at first. Eventually, the results were verified by others and John's theory was accepted.
In 1866, he turned his attention to the Leonid meteors on which Hubert Newton had previously worked and published results. Newton had showed that the longitude of the ascending node, which marked where the shower would occur was increasing. John showed that the Leonids traverse through the Solar System in an elongated elliptical orbit of 33.25 years. Furthermore, John showed that the cluster of meteors was influenced by perturbations from the larger gas giant planets Jupiter, Saturn and Uranus. This is considered one of the most important discoveries that John had made in his career.