LE VERRIER AND ADAMS' PLANET. 



would leave to futurity the decision of the question, whether these 

 deviations were due to errors of observation, or to an undiscovered 

 disturbing agent. We shall presently he enabled to appreciate 

 the sagacity of this reserve. 



7. The motions of the planet continued to be assiduously 

 observed, and were found to be in accordance with the tables for 

 about fourteen years from the date of the discovery of the planet. 

 About the year 1795, a slight discordance between the tabular 

 and observed places began to be manifested, the latter being a 

 little in advance of the former, so that the observed longitude L 

 of the planet was greater than the tabular longitude L'. After 

 this, from year to year, the advance of the observed upon the 

 tabular place increased, so that the excess L L' of the observed 

 above the tabular longitude was continually augmented. This 

 increase of L L' continued until 1822, when it became stationary, 

 and afterwards began to decrease. This decrease continued until 

 about 1830-31, when the deviation L L' disappeared, and the 

 tabular and observed longitudes again agreed. This accordance, 

 however, did not long prevail. The planet soon began to fall 

 behind its tabular place, so that its observed longitude L, which 

 before 1831 was greater than the tabular longitude L', was now 

 less ; and the distance I/ L of the observed behind the tabular 

 place increased from year to year, and still increases. 



It appears, therefore, that in the deviations of the planet from 

 its computed place, there was nothing irregular and nothing com- 

 patible with the supposition of any cause depending on the 

 accidental errors of observation. The deviation, on the contrary, 

 increased gradually in a certain direction to a certain point ; and 

 having attained a maximum, then began to decrease, which 

 decrease still continues. 



The phenomena must, therefore, be ascribed to the regular 

 agency of some undiscovered disturbing cause. 



8. It is not difficult to demonstrate that deviations from 

 its computed place, such as those described above, would 

 be produced by a planet revolving in an orbit having the 

 same or nearly the same plane as that of Uranus, which 

 would be in heliocentric conjunction with that planet at the 

 epoch at which its advance beyond its computed place attained 

 its maximum. 



Let A B c D E F, fig. 2, represent the arc of the orbit of Uranus 

 described by the planet during the manifestation of the perturba- 

 tions. Let N N' represent the orbit of the supposed undiscovered 

 planet in the same plane with the orbit of Uranus. Let a, b, c, 

 d, e, and / be the positions of the latter when Uranus is at the 

 points A, B, c, D, E, and F. It is therefore supposed, that Uranus 

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