The canals on MarsThe canals were discovered on Mars by Giovanni Virginio Schiaparelli in 1877. For obvious reasons the discovery created great excitement. Numerous maps of the canal pattern appeared and even if they were not always consistent with each other, this did not stop Percival Lowell from founding an observatory in Flagstaff, Arizona (USA) for the main purpose of investigating Mars and other planets. Many years later in the same observatory Lowell discovered Pluto and he was the first to conjecture that the canals represent waterways built by the inhabitants of Mars. And that was the state of affairs up to the seventies in the 20th century. Few were those who still believed in Marsians by that time, but only space probes sent towards Mars made it hundred percent clear that there are no canals on the planet. Why, yes, the photographs showed empty river-beds, various ravines, but all that is the effect of natural geological processes. Nothing to do with any kind of artificial constructions.
There seems to be no case similar to that of the Mars canals in the entire history of astronomy. For almost a century there was no doubt about their existence and the illusion was strong enough to make people spend a lot of money on research projects. It was only much later that the astronomers began to search for a proof that an illusion it was indeed. Experiment proved that the human eye tends to incorporate irregularly dispersed spots into a regular pattern, especially when single spots cannot be distinguished. But, after all, maybe it is not bad to have illusions? Perhaps without this particular illusion H.G. Wells would have never written his book on Martians, the famous observatory would have never come into existence and the interest of laymen in the universe would have been much smaller. Who knows?