48 'LIGHT SCIENCE FOR LEISURE HOURS. 



differential equations involved in the problem of the 

 lunar motions that is, when the eccentricity is made a 

 function of the time non-periodic or secular terms 

 appear in the expression for the moon's mean motion ' 

 and so on ? Let it suffice to say that Laplace had 

 considered only the effect of the sun in diminishing 

 the earth's pull on the moon, supposing that the slow 

 variation in the sun's direct influence on the moon's 

 motion in her orbit must be self-compensatory in long 

 intervals of time. Adams has shown, on the contrary, 

 that when this variation is closely examined, no such 

 compensation is found to take place ; and that the 

 effect of this want of compensation is to diminish by 

 more than one-half the effects due to the slow varia- 

 tion examined by Laplace. 



These views gave rise at first to considerable con- 

 troversy. Pontecoulant characterised Adams's pro- 

 cesses as f analytical conjuring-tricks ; ' and Leverrier 

 stood up gallantly in defence of Laplace. The contest 

 swayed hither and thither for awhile ; but gradually 

 the press of new arrivals on Adams's side began to 

 prevail. One by one, his antagonists gave way ; new 

 processes have confirmed his results, figure for figure ; 

 and no doubt now exists, in the mind of any astro- 

 nomer competent to judge, of the correctness of 

 Adams's views. 



But, side by side with this inquiry, another had 

 been in progress. A crowd of diligent labourers had 

 been searching with close and rigid scrutiny into the 

 circumstances attending ancient eclipses. A new light 



