“Little memory, no genius, much patience, and an everlasting curiosity about everything,” was how Giovanni Virginio Schiaparelli (Fig. 1.1) once described himself, but that self-deprecating review of his own intellectual capabilities belied his contribution to nineteenth-century astronomy. Although an observer possessed of keen perceptive abilities, he was also nearsighted and colorblind, crucial characteristics that likely influenced his judgment and left a particular imprint on how we now view the reliability of the human eye and brain in making useful astronomical observations.