North Polar Cap of Mars.

Percival Lowell (1855-1916) Mars and Its Canals. New York: Macmillan Co., 1911.

Percival Lowell founded his observatory in 1894 in Flagstaff, Arizona. Lowell Observatory became a famed site for research, and still exists today as a National Historic Landmark. Lowell used the observatory to study Mars. He held that a system of canals was visible that evidenced an intelligent, Martian race. He also believed in the existence of a ninth planet, which was eventually found by another astronomer and named Pluto (although astronomers recently downgraded Pluto to the status of a "dwarf planet").

His study of Martian polar caps, illustrated in his map shown here, was fundamental to his assertion that the planet has the proper environment and atmosphere to support life.