THE OUTER PLANETS. 119 



discovered. After much calculation Le Verrier, 

 in his third memoir (August 31, 1846), assigned 

 to the planet a position in the constellation 

 Aquarius. 



Meanwhile one of Le Terrier's papers happened 

 to reach Airy. Seeing its resemblance to Adams' 

 papers, which had been lying on his desk for 

 months, his scepticism vanished, and he sug- 

 gested to Challis that the planet should be 

 searched for with the Cambridge equatorial. In 

 July 1846 the search was commenced. The 

 planet was actually observed on August 4 and 

 12, but, owing to the absence of star maps, it 

 was not recognised. " After four days of observ- 

 ing," he wrote to Airy, " the planet was in my 

 grasp if I had only examined or mapped the 

 observations." 



Le Verrier wrote to Encke, the illustrious 

 director of the Berlin Observatory, desiring him 

 to make a telescopic search for a planetary object 

 situated in the constellation Aquarius, as bright 

 as a star of the eighth magnitude and possessed 

 of a visible disc. " Look where I tell you," 

 wrote the French astronomer, " and you will see 

 an object such as I describe." Encke ordered 

 his two assistants, Galle and D' Arrest, to make 

 a search on the night of September 23, 1846. 

 In a few hours Galle observed an object not 



