26 HISTORY OF ASTRONOMY. 



was not there to be found. An American astronomer, 

 Mr. Sears C. "Walker, was more fortunate. Mr. Walker 

 proceeded in the following manner. He first computed 

 the orbit which best represented all the observations 

 which had been made at the "Washington observatory, 

 as well as those which had been received from Europe. 

 He then computed the planet's probable place for a long 

 series of preceding years, and sought among the records 

 of astronomers for observations of stars in the neighbor- 

 hood of the computed path. Bradley, Mayer, and La- 

 caille have left us an immense collection of observations, 

 yet they seldom recorded stars so small as the body in 

 question. Among the observations of Piazzi, no one 

 was found which could be identified with the planet. 

 The Madras observations were generally confined to the 

 stars of Piazzi's catalogue. The Paramatta catalogue 

 seldom extends north of the thirty -third parallel of south 

 declination ; and Bessel, in preparing his zones of 

 75,000 stars, did not sweep far enough south to com- 

 prehend the planet. The only remaining chance of 

 finding an observation of the planet was among the 

 observations of Lalande. The Histoire Celeste Frangaise 

 embraces 50,000 stars, and Mr. Walker soon found that 

 Lalande had swept over the supposed path of the planet 

 on the 8th and 10th of May, 1795. He accordingly 

 computed more carefully the place of the planet for this 

 period, making small variations in the elements of the 

 orbit, so as to include the entire region within which the 

 planet could possibly have been comprised. He then 



