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172 a musician in Bath, Herschel "found that the poles of Mars were distinguished with remarkable luminous spots." He believed that, by observing them carefully, he might secure a key to a knowledge of the planet, and its history, the length of its day, its atmosphere, its seasons. These observations were continued during six or seven years. Sometimes he saw a well-marked lucid spot on Mars: "it is its south pole, for it remains in the same place, while the dark equatorial spots perform their constant gyrations: it is nearly circular." It was not only circular; "it was very brilliant and white." At other times he saw also another "lucid spot" at the planet's north pole. Occasionally both spots were seen, but the one was "thicker," or "much thicker," than the other, while the thinner was, or seemed to be, longer. After six years of watching he writes, "The white polar spot increases in size; it is very luminous." The conclusions he drew from these notes in his journal, and from his calculations to ascertain the seasons on Mars, must have been listened to by those who first heard them read as if they were a page or two from a romance by Fielding or Smollett. We give them in Herschel's own words.

"The analogy between Mars and the earth is, perhaps, by far the greatest in the whole solar system. . . . If then we find that the globe we inhabit has its polar regions frozen and covered with mountains of ice and snow, that only partly melt when alternately exposed to the sun, I may well be permitted to surmise that the same causes may probably have the same effect on the globe of Mars; that the bright polar spots are owing to the vivid reflection of light from frozen regions; and that the reduction of those spots is to be