238 HISTORY OF PHYSICAL ASTRONOMY. 



planets. To determine the equation of the center 

 of a body which revolves so slowly, would, accord- 

 ing to the ancient methods, have required many 

 years : but Laplace contrived methods by which the 

 elliptical elements were determined from four ob- 

 servations, within little more than a year from its 

 first discovery by Herschel. These calculations 

 were soon followed by tables of the new planet, 

 published by Nouet. 



In order to obtain additional accuracy, it now 

 became necessary to take account of the perturba- 

 tions. The French Academy of Sciences proposed, 

 in 1789, the construction of new Tables of this 

 Planet as its prize-question. It is a curious illus- 

 tration of the constantly accumulating evidence 

 of the theory, that the calculation of the pertur- 

 bations of the planet enabled astronomers to dis- 

 cover that it had been observed as a star in three 

 different positions in former times ; namely, by 

 Flamsteed in 1690, by Mayer in 1756, and by Le 

 Monnier in 1769. Delambre,, aided by this dis- 

 covery and by the theory of Laplace, calculated 

 Tables of the planet, which, being compared with 

 observation for three years, neyer deviated from it 

 more than seven seconds. The Academy awarded 

 its prize to these Tables, they were adopted by the 

 astronomers of Europe, and the planet of Herschel 

 now conforms to the laws of attraction, along with 

 those ancient members of the known system from 

 which the theory was inferred. 



