Roger of Salisbury, in fact, when placed at the head of the Exchequer, found a great difference between the weight and the actual value of the coin received.
Both Schiaparelli and Lowell were at first so surprised at this phenomenon that they thought it must be an optical illusion, and it was only after many observations in different years, and by the application of every conceivable test, that they both became convinced that they witnessed a real feature of the planet's surface.