Percival Lowell's Quest
Lowell had become interested in studying what he thought were artificial canals on Mars, and in 1894 established the Lowell Observatory in Flagstaff, Arizona. Mars wasn't the only planet that interested him, and in 1905, he began a search for the ninth planet.
Besides being able to apply his mathematical skills, Lowell had his own observatory at his disposal, something John Couch Adams had lacked when he predicted Neptune's position. Lowell's staff conducted a photographic survey of the sky, with Lowell's calculations thrown in to help narrow the search.
Lowell initially kept his search a secret, so that others might not steal his project. However, when the extreme difficulties of finding a planet became evident, Lowell was no longer worried about an opportunistic astronomer taking the glory, and by 1908 was publicly calling his elusive quarry "Planet X."
By 1908, William Pickering was also conducting a search for what he called "Planet O." Pickering had helped Lowell set up his observatory, though he became rather critical of Lowell's ideas that Mars held intelligent life.
Over the next eight years, Lowell applied himself and his staff with increasing vigor to the search. He hired Elizabeth Williams to help with the computations, and improved the equipment, upgrading his search with the 40-inch reflector telescope, the largest at the observatory. By the end of 1915, no planet had been discovered.
Lowell's discouragement deepened when the American Academy of Arts and Sciences declined to publish his paper on his theoretical and observational efforts to find the ninth planet. After this, Planet X was no longer mentioned in his writings.
By July of 1916, the photographic search ended. Ironically, Planet X appeared twice in this set of plates, but being much dimmer than predicted, it went unrecognized as the sought-after prize. On November 12, 1916, Lowell died of a massive stroke at his observatory.
Lowell's LegacyThe search for Planet X did not end with Lowell's death. His will provided for a million dollars to support the observatory, and designated his assistant Vesto Slipher as director of the observatory. Lowell also left quite a sum to his wife Constance. The observatory staff was ready to use the observatory endowment to carry on Lowell's work, but Lowell's widow was not enthusiastic about this arrangement.
She contested the will, and by the time the court battles ended and the estate was settled in 1927, much of the money had gone toward legal fees. Still, Planet X waited, heedless of the problems that delayed its discovery. The observatory ordered a new 13-inch telescope, and prepared to resume Lowell's quest.