The networked appearance of the canals owed its existence more to the cartographic process than to any reality on the Martian surface.
Once this network existed on the map, however, it became a powerful icon. Popular Sunday papers frequently published geometric images of Mars; lecturers prepared lantern slides showing canal maps; and books about Mars used the canal-map to augment their arguments that Mars was inhabited. This cartographic icon performed significant visual work, conveying the objectivity of cartography, the idea that Mars was fundamentally visible or legible through science, and the near-certainty of intelligent life on Mars. From a present-day perspective, when we know this was all based on an optical illusion, the near-certainty may seem fantastic or laughable. At the time, however, this was the most reasonable interpretation of the data available, given the iconic cartographic format in which these data made their way into scientific narratives and popular consciousness.
New Imagery and the Decline of the Martian Canals
So far, this essay has shown that map-related controversies spurred increasing interest in the red planet, that Mars maps established the initial authority of the inhabited-Mars hypothesis, and that the iconic image of Mars that was ever-present during the popular canal mania was purely an artifact of cartographic projection. To further appreciate the iconic power of the map, this section will also examine the role cartography played in contributing to declining belief in Martian inhabitants in the early twentieth century. The concept of the canals had always been challenged, whether through criticism of Schiaparelli’s artistic skills, through insistence that the lines were merely optical illusions, or through debates over whether the existence of lines necessarily indicated the existence of intelligent beings. It was not until 1909, however, that those challenges really began to have an impact.
Somewhat ironically, it was the champion of the inhabited-Mars hypothesis, Percival Lowell, who initiated the end of his own era. By 1900, Lowell had garnered significant popular interest in his inhabited-Mars hypothesis, prompting several professional American astronomers to oppose his interpretations rather vocally in the popular press. In the ensuing battle for public opinion with these critics, Lowell pioneered a new method for photographing the Martian surface. In 1905, he used this new technology at his Arizona observatory to capture photographs that indeed showed some dark markings in areas where Lowell had drawn canals on the maps. Lowell circulated these small photographs to astronomers and other scientists, claiming they discredited any charges of optical illusion because of the perfect objectivity of the photographic format. When Lowell’s critics persisted with their criticism, he sent a very high-profile expedition to South America to get additional photographs of Mars in 1907.
