American astronomer Percival Lowell at his observatory in Flagstaff, Arizona. In this 1914 photograph Lowell is seen observingVenus high in the daytime sky, with the refracting telescope's 24-inch (61 cm) lens diameter stopped down to 3 inches (7.6 cm) to reduce the effects of atmospheric turbulence.
Lowell has been described as "the most influential popularizer of planetary science in America before Carl Sagan". His efforts to find Planet X eventually led to the discovery of Pluto, 14 years after his death. Pluto was named partly in recognition of Lowell's efforts, although the Planet X theory was subsequently disproved.
