LE VEREIER AND ADAMS* PLANET. 



It is then apparent, that from A to D the disturbing force, 

 accelerating the orbital motion, will transfer Uranus to a position 

 in advance of that which it would otherwise have occupied ; and 

 after passing D, the disturbing force retarding the planet's motion 

 will continually reduce this advance, until it bring back the 

 planet to the place it would have occupied had no disturbing force 

 acted; after which, the retardation being still continued, the 

 planet will fall behind the place it would have had if no disturb- 

 ing force had acted upon it. 



Now it is evident that these are precisely the kind of dis- 

 turbing forces which act upon Uranus ; and it may, therefore, 

 be inferred that the deviations of that planet from its com- 

 puted place are the physical indications of the presence of 

 a planet exterior to it, moving in an orbit whose plane either 

 coincides with that of its own orbit, or is inclined to it at a 

 very small angle, and whose mass and distance are such as to 

 give to its attraction the degree of intensity necessary to pro- 

 duce the alternate acceleration and retardo^'on which have been 

 observed. 



Since, however, the intensity of the disturbing force depends 

 conjointly on the quantity of the disturbing mass and its distance, 

 it is easy to perceive that the same disturbance may arise from 

 different masses, provided that their distances are so varied as to 

 compensate for their different weights or quantities of matter. A 

 double mass at a fourfold distance will exert precisely the same 

 attraction. The question, therefore, under this point of view, 

 belongs to the class of indeterminate problems, and admits of an 

 infinite number of solutions. In other words, an unlimited 

 variety of different planets may be assigned, exterior to the sys- 

 tem which would cause disturbances observed in the motion of 

 Uranus, so nearly similar to those observed, as to be distinguishable 

 from them only by observations more extended and elaborate than 

 any to which that planet could possibly have been submitted since 

 its discovery. 



9. The idea of taking these departures of the observed from the 

 computed place of Uranus, as the data for the solution of the 

 problem to ascertain the position and motion of the planet which 

 could cause such deviations, occurred, nearly at the same time, 

 to two astronomers, neither of whom at that time had attained 

 either the age or the scientific standing which would have raised 

 the expectations of achieving the most astonishing discovery of 

 modern times. 



H. Le Verrier, in Paris, and Mr. J. C. Adams, Fellow and 

 Assistant Tutor of St. John's College, Cambridge, engaged in the 

 investigation, each without the knowledge of what the other was 

 178 



