Percival Lowell's calculations showed that the mass of Mars was much less than that of Earth. Since Lowell assumed that Mars was largely covered by water, he theorized that this difference in mass meant that Mars was rapidly losing water vapor: its oceans were literally disappearing into thin air. Lowell further believed that this dehydration of the planet had accelerated Martian evolution and brought forth a race of highly intelligent beings who had built canals as a survival measure.
Through his telescope, Lowell had seen snowy glaciers at both ends of the planet. He had also noticed that during the Martian summer a deep blue crescent formed along the southern ice cap. As the summer progressed, the ice cap disappeared altogether. So when the planet's vast seas evaporated, the only sources of water left on Mars must be its north and south poles. Lowell believed that the Martians were siphoning off water from the poles and pumping it through a labyrinthine plumbing system across the planet to their few surviving cities. Lowell reasoned that an engineering feat of this magnitude would require so much knowledge and such thorough global cooperation that the inhabitants of Mars must be wise and peaceable. They were desperately working to slow their inevitable end.
The public was infatuated with Lowell's story, but astronomers of the day responded with skepticism.
