It's not quite that cut and dry, Lowell's work was not only authoritative, it was corroborated (and challenged, too) by many of his contemporaries. But no one dismissed it out of hand. The issue is how he, and his followers, viewed the available evidence through mental filters which dismissed objections and gave undue weight to supporting facts. We're all guilty of this, to some extent or another, we can afford to be charitable towards him. He did the best with what he had available.

Mars is at the extreme boundary of visual observation, oppositions are infrequent and favorable ones are rare, no two are alike, and very often weather (here AND on Mars) can ruin the observations over the short observing seasons (several weeks long and several years apart).

The visual appearance of the planet is similar to that of the moon with the naked eye, even through the best telescopes and ideal atmospheric conditions. It was not unusual for only one or two telescopes to be available world-wide when a favorable opposition took place. When opposition time coincided with an ecliptic position in the southern hemisphere, most American and European telescopes were ineffective, and not too many 'scopes or astronomers worked down under. Oddly enough, long-focus Victorian refractors were even better suited for this kind of work than today's mega-reflectors. From these brief, intermittent observations, planetary observers tried to reconstruct records of long term Martian phenomena, communicating only by telegraph and journals through the mail. Tools routinely used today such as fast films, digital detectors, and high-contrast color filters either did not exist or were in their infancy. It's not surprising mistaken ideas took root, were passed on uncritically and survived much longer than they should have. When data is scarce and highly subjective, speculation creeps in, and of course, people tend to go with what they believe as much as with what they know. It's just human nature.

Knowing what we know now, I would suspect many of his non-canal observations would be suspect today. Lowell's desire to find supporting evidence for his ideas tended to influence the kind of evidence he took note of and the kind he was likely to dismiss. Anyone who has debugged code knows this, no matter how sure you are you've found the cause of the problem, you still have to run a test to be sure. In Lowell's case, the test was over a half-century in the future. Still, we can take comfort in the fact than when the spacecraft data did finally become available, science quickly accepted it.

Still, if you've ever actually studied Lowell's hand-drawn sketches of the Martian surface, you will get a glimpse into the mystery and romance of science, and of the scientific imagination. There is a strange, alien beauty, an abstract elegance to those pastel shades and geometric canal networks, the graceful Latin and Greek mythological references in the place names, that awesome vision of a dwindling race on a dying world struggling with all their technology and organization to preserve their doomed civilizatiion. Those beautiful maps and globes inspired by Lowell may not tell us much about the planet, but they reveal volumes about the souls of the men who drew them and who felt it was important enough to dedicate their lives to that work. It's kids who were brought up and nourished by that vision who grew up to design the robot probes that finally revealed the true face of the red planet. Today's Mars owes a lot to Lowell's.