xii PREFACE TO THE 



express application from M. Le Verrier, recommend- 

 ing him to endeavour to recognize the stranger by 

 its having a visible disk. Professor Challis, at the 

 Observatory of Cambridge, was looking out for the 

 new planet from July 29, and saw it on Aug. 4, and 

 again on Aug. 12, but without recognizing it, in 

 consequence of his plan of not comparing his obser- 

 vations till he had accumulated a greater number 

 of them. On Sept. 29, having read for the first time 

 M. Le Verrier's second paper, he altered his plan, 

 and paid attention to the physical appearance rather 

 than the position of the star. On that very evening, 

 not having then heard of M. Le Galle's discovery, he 

 singled out the star by its seeming to have a disk. 



M. Le Verrier's mode of discussing the circum- 

 stances of Uranus's motion, and inferring the new 

 planet from these circumstances, is in the highest 

 degree sagacious and masterly. Justice to him 

 cannot require that the contemporaneous, though 

 unpublished, labours of Mr. Adams of St. John's 

 College, Cambridge, should not also be recorded. 

 Mr. Adams made his first calculations to account 

 for the anomalies in the motion of Uranus, on the 

 hypothesis of a more distant planet, in 1843 1 . At 



1 Mr. Adams informs me that as early as 1841 he conjectured 

 the existence of a planet exterior to Uranus, and recorded in a 



