46 HISTORY OF ASTRONOMY. ' 



the sun between 29*6 and 35'2. It is not obvious how 

 this last statement can be reconciled with the limits 

 published in 1846. Doubtless Le Yerrier has discovered 

 that the limits which he first assigned were erroneous. 

 If we compare the predicted mean distance with that 

 deduced from the observations, we shall find the error 

 of the former to amount to one fifth of the whole 

 quantity. 



III. The error in the eccentricity of Neptune. 



Le Yerrier assigned to the orbit of his planet an ec- 

 centricity of 0'1076; the computations of Mr. Walker 

 make the eccentricity of Neptune 0*0087. 



The discrepancy is considerable ; but Le Yerrier states 

 that if we admit an uncertainty of 5" only in the modern 

 data, the eccentricity of the body producing the irreg- 

 ularities of Uranus may be chosen arbitrarily between 

 0*2031 and 0'0592 ; and if we admit an uncertainty of 

 7" or 8" in the modern data, the eccentricity may have 

 any value between 0*25 and zero. Professor Peirce has 

 shown that the planet Neptune, with an eccentricity 

 almost zero, reconciles all the modern observations of 

 Uranus within 3". 



IY. Error of the computed mass of Neptune. 



The mass assigned by Le Yerrier to his predicted 

 planet was -g-^Vo f the sun's mass ; but he adds, that if 

 we admit an uncertainty of 5" in the data, this mass may 

 have any value between TT Vo- and TT^O-- The mass of 

 Neptune deduced by Struve, from his own observations 

 of the satellite, is 744-94 ; but the mass deduced from Las- 



