42 HISTORY OF ASTRONOMY. 



sell's satellite. By his computations, the great anomalies 

 which had been observed, and which are represented on 

 page 12, almost entirely disappear. All the modern ob- 

 servations are represented quite as well as by the theories 

 of Adams and Le Yerrier, and the observation of 1690 

 much better. The error of Flamsteed's observation of 

 1690, according to Adams's computation, was 50", and ac- 

 cording to Le Terrier's computation, 20"; but according 

 to Peirce's theory, this observation is represented within a 

 single second. 



So then the anomalies of Uranus, which had so long 

 perplexed astronomers, are perfectly accounted for. But 

 it is obvious, from a glance at the diagram on page 30 , 

 that the planet actually discovered is moving in an orbit 

 considerably different from what had been computed, so 

 that it has been claimed by Professor Peirce that Neptune 

 is not the planet whose existence had been predicted by Le 

 Verrier. Is this discrepancy between the observed and 

 predicted orbits of a serious nature ; and if so, how is it 

 to be accounted for ? This question has been fully dis- 

 cussed by Le Yerrier himself. Le Yerrier attempted to 

 deduce the position of a new planet, by studying the ir- 

 regularities in the motion of Uranus. The data which 

 he was obliged to employ, were liable to some uncertainty. 

 This uncertainty of the data did not result merely from 

 the uncertainty of the observations, but from two other 

 causes, viz., a possible error in the mass of Saturn suffi- 

 cient to add 3" to the uncertainty of the observations, and 

 from the possible influence of a planet situated beyond 



