ZOXE OF PLANETS BETWEEN MARS AND JUPITER. 57 



assigned the position of a star which did not really exist. 

 On the 1st of January, 1801, Piazzi observed a small 

 star, which on the following evening appeared to have 

 changed its place. On the 3d he repeated his observa- 

 tions, and he now felt assured that the star had a retro- 

 grade motion in the zodiac. On the 24th of January 

 he transmitted an account of his discovery to Oriani and 

 Bode, communicating the position of the star on the 3d 

 and 23d of that month. He continued to observe the 

 star until the llth of February, when, he was seized 

 with a dangerous illness, which completely interrupted 

 his labors. His letters to Oriani and Bode did not reach 

 those astronomers until the latter end of March, at which 

 time the planet had approached too near the sun 'to 

 admit of further observations, and it was necessary for 

 this purpose to wait until the month of September, when 

 the planet would have extricated itself from the solar 

 rays. Its re-discovery, after the lapse of so considerable 

 a period, subsequent to the most recent observation, 

 could not be accomplished without a pretty accurate 

 knowledge of the orbit in which it was moving; but 

 the data communicated by Piazzi were insufficient for 

 this purpose. After some delay he communicated to 

 astronomers all the observations made by himself down 

 to the end of February. Professor Gauss found that 

 they might all be satisfied within a few seconds by an 

 elliptic orbit, of which he calculated the elements; and 

 with the view of aiding astronomers in searching for the 

 planet, he computed an ephemeris of its motion for 



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