10 HISTORY OF ASTRONOMY. 



place of this planet. The materials for the construction 

 of these tables consisted of forty years' regular obser- 

 vations at Greenwich and Paris since 1781, and the 

 nineteen accidental observations, reaching back almost 

 a century further. Upon comparing these observations, 

 Bouvard found unexpected difficulties. He was unable 

 to find any elliptic orbit, which, combined with the 

 perturbations by Jupiter and Saturn, would represent 

 both the ancient and the modern observations. When 

 he attempted to unite the ancient with the modern 

 observations, the former might be tolerably well re- 

 presented, but the latter exhibited discordances too great 

 to be ascribed to errors of observation. Not being 

 able to explain this discrepancy in any satisfactory man- 

 ner, he rejected the ancient observations, and founded 

 his tables upon the observations since 1781. " It being 

 necessary," says he, "to decide between the ancient and 

 the modern observations, I have held to the modern 

 ones as being the most likely to be accurate, and I leave 

 it to time to show whether the difficulty of reconciling 

 the two sets of observations depends . upon the inac- 

 curacy of the ancient ones, or on some foreign and un- 

 known influence to which the pla.net is subjected" 



These tables represent very well the observations of 

 the forty years from which they were derived ; but 

 soon after 1821, new discrepancies began to appear, 

 which have lately increased with great rapidity. In 

 1832, the discordance between the observed and com- 

 puted plaoe of tlje planet, Amounted to nearly half a 



