On the first day of the last century (January 1, 1801), Piazzi, an astronomer devoted to the sky, was observing at Palermo the small stars of the constellation Taurus, and noting their exact positions, when he remarked one which he had never seen before. The following evening (January 2) he directed his telescope again toward the same region of the sky, and remarked that the star was no longer at the point where he had seen it the day before, and that it had retrograded by 4′. It continued to retrograde up to the 12th, stopped, and then moved in the direct way—that is to say, from west to east. What was this moving star? The idea that it might be a planet did not immediately occur to the mind of the observer, and he took it for a comet, as William Herschel had done in 1781, when he discovered Uranus. However, the skilful Sicilian observer was a member of an association which had for its special object the search for an unknown planet between Mars and Jupiter. From the earliest times of modern astronomy Kepler had described the disproportion, the void which exists between the orbit of Mars and that of Jupiter. If we omit, in fact, the orbit of the small planets or asteroids, we notice that the four planets, Mercury, Venus, the earth, and Mars, are in some measure crowded quite close to the sun, while Jupiter, Saturn, Uranus, and Neptune extend far into immensity. The law of Titius indicates a number, the number 28, as not being represented by any planet. It was in 1772 that this _savant_ published this relation in a German translation which he had made of the _Contemplation de la Nature_ of Charles Bonnet. Bode, Director of the Berlin Observatory, was so astonished at the coincidence that he announced this arithmetical relation as being a real law of nature, and spoke of it in such a way that it is generally known only by his name. He even organized an association of twenty-four astronomers to explore each hour of the Zodiac and search for the unknown. This systematic exploration had not yet produced any result when, by the merest chance, Piazzi saw his moving star, and at first believed it to be a comet. But on receipt of the news, Bode was convinced that this was the looked-for planet. The new planet was found to be at the distance 2.77, and to revolve within a few days of the predicted period. Piazzi gave to the new body the name of _Ceres_, the protecting divinity of Sicily in the “good old times” of mythology.