186 THE HISTORY OF SCIENCE 



Almost immediately, however, after the publica- 

 tion of the tables, fresh discrepancies arose between 

 computation and observation. At the first meeting 

 of the British Association in 1832 Professor Airy 

 in a paper on the Progress of Astronomy showed 

 that observational data in reference to the planet 

 Uranus diverged widely from the tables of 1821. 

 In 1833 through his influence the " reduction of all 

 the planetary observations made at Greenwich from 

 1750 ' was undertaken. Airy became Astronomer 

 Royal in 1835, and continued to take special inter- 

 est in Uranus, laying particular emphasis on the fact 

 that the radius vector assigned in the tables to this 

 planet was much too small. 



In 1834 the Reverend T. J. Hussey, an amateur 

 astronomer, had written to Airy in reference to the 

 irregularities in the orbit of Uranus : " The appar- 

 ently inexplicable discrepancies between the ancient 

 and modern observations suggested to me the possi- 

 bility of some disturbing body beyond Uranus, not 

 taken into account because unknown. . . . Subse- 

 quently, in conversation with Bouvard, I inquired if 

 the above might not be the case." Bouvard answered 

 that the idea had occurred to him ; indeed, he had 

 had some correspondence in reference to it in 1829 

 with Hansen, an authority on planetary perturba- 

 tions. 



In the following year Nicolai (as well as Valz) 

 was interested in the problem of an ultra-Uranian 

 planet in connection with the orbit of Halley's comet 

 (itself the subject of a striking scientific prediction 

 fulfilled in 1758), now reappearing, and under the 

 disturbing influence of Jupiter. In fact, the proba- 



