138 NINTH ANNUAL REPORT OF 



while engaged in constructing his great catalogue of stars, was induced 

 carefully to examine, several nights in succession, a part of the constel- 

 lation Taurus, in which Wollaston, by mistake, had assigned the posi- 

 tion of a star which did not really exist. On the first of January, 1801, 

 Piazzi observed a small star which, on the following evening, appeared 

 to have changed its place. On the third, he repeated his observations, 

 and he now telt assured that the star had a retrograde motion in the 

 zodiac. He continued to observe the star until the 11th of February, 

 when he was seized with an illness which interrupted his labors. After 

 the planet had approached too near the sun to admit of further obser- 

 vations for that season, Piazzi communicated to astronomers all his ob- 

 servations. Professor Gauss found that they might all be satisfied by 

 an elliptic orbit, of which he computed the elements. The planet was 

 re-discovered on the 31st of December, almost exactly in the place 

 which had been predicted b}^ Gauss ; and it received the name of 

 Ceres. 



The distance of Ceres from the sun was found to be almost exactl}- 

 the same as had been assigned by Bode's law. In this respect, there- 

 fore, the newly discovered planet harmonized with the other bodies of 

 the system to which it belonged. The new planet was, however, ex- 

 cessively minute, its diameter, according to Herschel's measurements, 

 amounting to only one hundred and sixty-one miles. 



The discovery of this planet was soon tbllov/ed by another of a simi- 

 lar nature. Dr. Olbers, while engaged in searching for Ceres, had 

 carefully studied the positions of ail the small stars lying near her path. 

 On the 28lh of March, 1802, after observing Ceres, he swept over the 

 vicinity with an instrument termed a " comet seeker," and was aston- 

 ished to find a star of the seventh magnitude in a position where he 

 was sure no star had been visible the preceding month. In less than 

 three hours, he found that its place had changed. On the following 

 evening he looked again for his star, and found that its motion was un- 

 questionable. The elements of its orbit were soon determined by Pro- 

 fessor Gauss, who found that its distance from the sun was nearly the 

 same as that of Ceres ; and it received the name of Pallas. 



A comparison of the relative magnitudes of the planetary orbits had 

 suggested the existence of an unknown planet revolving between Mars 

 and Jupiter. Instead of one planet, however, two had been discovered. 

 Olbers remarked that there was a point where the orbits of these two 

 bodies approached very near each other ; and he conjectured that they 

 might possibly be the fragments of a larger planet, which had been 

 split in pieces by some tremendous catastrophe ; and he intimated that 

 there might be many more fragments which had not yet been dis- 

 covered. He also inferred that, according to this theory, the orbits of 

 all the fragments would have two common points of intersection situated 

 in opposite parts of the heavens, through which every fi-agment must 

 pass in the course of each revolution. He therefore proposed every 

 month to search carefully the two points of the heavens in which the 

 orbits of Ceres and Pallas were Ibund to intersect each other. The 

 speedy discovery of a third planet tended to confirm the truth of this 

 hypothesis. 



On the 1st of September, 1804, Professor Harding discovered a small 



