Having moved to Flagstaff, Arizona, I felt compelled to learn more about Percival Lowell and his theories about Mars. My source was Mars as the Abode of Life
(Brohan Press, 1908), which was the final version of a theory most famously developed in Mars and its Canals
(McMillan, 1906). Mars as the Abode of Life includes Lowell's attempts to answer (or dismiss) critics of his theories, most notably Alfred Russell Wallace* in his Is Mars Habitable? A critical examination of Professor Percival Lowell's book
The subject makes for a fascinating study in the history of science. Without radioactive decay, the internal heat of the planets is generated from the mechanical energy of the particles falling together to form them. Without continental drift or plate tectonics, geographic features (mountains and valleys; continents and ocean basins) formed in place as the crust cooled, contracted, and cracked or buckled. Volatiles are lost both by escape at the top of the atmosphere (which is correct) but also by constantly seeping through cracks and fissures into the planetary interior. Craters and maria on the Moon are caused by extensive volcanism, in the past if not recent history.
It's important to remember that up to this point astronomy was conducted by peering through telescopes by eye and recording observations in sketches (like a court reporter). Schiaparelli's canali
were accepted as real even by Lowell's critics, because they had been consistently seen and recorded by some of the most able observers using the best equipment under the most favorable conditions available. (Lowell claimed to have a photographic plate capturing their image, but I haven't been able to find a copy.) Lowell was convinced that Mars was featureless and flat, because he'd never been able to observe mountain peaks casting long shadows near sunset, or remaining in sunlight after the terminator had passed.
Google Earth has a set of overlay images of Mars based on Lowell's (and others') hand-drawn maps. It's interesting to toggle between these and the maps generated from spacecraft visiting Mars (the Viking orbiter images are complete and easy to read), to see what he got right and what was just flat wrong.
*Wallace is best remembered for his work on speciation by natural selection, and particularly its effect on the geographic distribution of species (cf. Wallace Line