ON GEOLOGICAL TIME. 39 



an error of a technical kind in Laplace's process 

 the omitting to take into account in the tangential 

 component of the sun's disturbing force on the 

 moon, the disturbing influence of the variation of 

 the eccentricity of the earth's orbit, and he worked 

 out the theory with this correction. 



17. The result, roughly stated, was to halve 

 the amount of acceleration calculated by Laplace 

 and to leave half of Dunthorne's observed relative 

 acceleration of the moon to be accounted for 

 otherwise. In 1853, Adams communicated to 

 Delaunay, one of the great French mathematicians, 

 his final result, that at the end of a century the 

 moon is 57 seconds of angle in advance of the 

 position she had when relatively to the meridian 

 of the earth, according to the angular velocity of 

 the moon's motion at the beginning of the century, 

 and the acceleration of the moon's motion truly 

 calculated from the various disturbing causes then 

 recognised. This, then, shows an unaccounted for 

 gain per century of n"'4 per century of angular 

 velocity of the moon's motion, on the hypothesis 

 that the earth's angular velocity is uniform. 



