Page "Percival Lowell" Paragraph 8

Lowell's greatest contribution to planetary studies came during the last decade of his life, which he devoted to the search for Planet X, a hypothetical planet beyond Neptune.

Lowell believed that the planets Uranus and Neptune were displaced from their predicted positions by the gravity of the unseen Planet X. Lowell started a search program in 1906 using a camera in aperture.

The small field of view of the reflecting telescope rendered the instrument impractical for searching.

From 1914 to 1916, a telescope on loan from Sproul Observatory was used to search for Planet X.

Although Lowell did not discover Pluto, Lowell Observatory ( 690 ) did photograph Pluto in March and April 1915.