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 of stuff as our Earth, and reflect the Sun's light as the Earth and the other planets do; but being so tiny they cannot reflect much of it and are consequently very hard to see. Most of the brightest of them have probably been found by this time, but every year more and more faint ones are found, so that we scarcely know whether there is any limit to their number. As regards distance from the Sun, they differ considerably among themselves, but with one or two rare exceptions they agree to keep within the gap between Mars and Jupiter. Now in Bode's time this was a real gap since none of the minor planets were known, and Bode thought that there must be a planet to fill the gap. The idea of a number of little planets doing duty for a big one had not at that time occurred to any one: it was merely thought that there was one missing planet, and Bode set the police on the track of the culprit. This may sound a strange statement; what he actually did was to get a number of astronomers to agree among themselves to watch different parts of the sky for the missing planet; but the little band of searchers were jokingly called the "astronomical police," so that my statement is not far wrong. It must have been mortifying to them when the culprit was first seen by an outsider (sometimes that happens to our earthly police in spite of their vigilance). Another astronomer called Piazzi, who was not looking for the planet at all, happened to find it; he watched it for a few nights to be sure of it, and sent a note of its position to a brother astronomer—one of the "police," but the post travelled very slowly in those days when there were no railways, so that it was a long time