SCIENTIFIC PREDICTION 185 



It might naturally be supposed that these so- 

 called ancient observations would lead to a ready 

 determination of the planet's orbit, mass, mean dis- 

 tance, longitude with reference to the sun, etc. The 

 contrary, however, seemed to be the case. When 

 Alexis Bouvard, the associate of Laplace, prepared 

 in 1821 tables of Uranus, Jupiter, and Saturn on 

 the principles of the Mecanique Celeste, he was un- 

 able to fix an orbit for Uranus which would harmo- 

 nize with the data of ancient and modern observa- 

 tions, that is, those antecedent and subsequent to 

 Herschel's discovery in 1781. If he computed an 

 orbit from the two sets of data combined, the re- 

 quirements of the earlier observations were fairly well 

 met, but the later observations were not represented 

 with sufficient precision. If on the other hand only 

 the modern data were taken into account, tables 

 could be constructed meeting all the observations 

 subsequent to 1781, but failing to satisfy those prior 

 to that date. A consistent result could be obtained 

 only by sacrificing the modern or the ancient ob- 

 servations. " I have thought it preferable," says Bou- 

 vard, " to abide by the second [alternative], as being 

 that which combines the greater number of proba- 

 bilities in favor of the truth, and I leave it to the 

 future to make known whether the difficulty of rec- 

 onciling the two systems result from the inaccuracy 

 of ancient observations, or whether it depend upon 

 some extraneous and unknown influence, which has 

 acted on the planet." It was not till three years after 

 the death of Alexis Bouvard that the extraneous in- 

 fluence, of which he thus gave in 1821 some indica- 

 tion, became fully known. 



