THE SEARCH FOR THE PLANET NEPTUNE BY PROFESSOR CHALLIS. 



[From the Astronomische Nackrichten. No. 583 (1846). Pp. 101106.] 



CAMBRIDGE OBSERVATORY, 



October 21, 1846. 



My more immediate purpose in writing to you at present, is to give 

 some account of observations which I undertook this summer in search of the 

 recently-discovered planet. Mr Adams, a young Cambridge mathematician, 

 had for a long time turned his attention to the perturbations of Uranus, 

 and in the autumn of last year communicated to me and to Mr Airy, 

 the Astronomer Royal, values which he had obtained of the heliocentric 

 longitude, mass, eccentricity of orbit, and longitude of perihelion of a sup- 

 posed disturbing planet, revolving at a mean distance from the Sun about 

 double that of Uranus. These results were deduced entirely from a con- 

 sideration of perturbations of Uranus not otherwise accounted for. M. Le 

 Verrier, by an investigation published in June last, obtained almost precisely 

 the same heliocentric longitude which Mr Adams had arrived at. This 

 coincidence from two independent sources very naturally inspired confidence 

 in the theoretical deductions, and accordingly Mr Airy shortly after suggested 

 to me the employing of the Northumberland telescope of this Observatory 

 in a systematic search after the planet. I commenced observing July 29. 



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