THE VAGARIES OF AN ORBIT. 375 



as it ascended, just as you have seen the earth's shadow in an 

 eclipse of the moon ohiiterate the silvery radiance of the lunar 

 disc — finally reaching ridge and summit and loftiest peak, and lo, 

 it was night, the ruddy orb of Mars over the now ink-black top 

 of Buachaill-Etive putting the fact beyond all question ; and, while 

 our fair companion went for a stroll along the beach, gaily singing 

 a merry roundelay as became her innocence and her years, we 

 retired in a mood of mind that, while it was pleasant upon the 

 whole, had yet a tinge of sadness about it, to our study and 

 our books. 



France has recently lost one of her greatest men by the death of 

 M. Leverrier, her distinguished astronomer, the most distinguished 

 astronomer, it is not too much to say, of the present century. 

 Many, indeed, achieved greater triumphs with the telescope, for 

 with the telescope Leverrier did comparatively little ; it was as a 

 mafhematical astronomer that he was unrivalled. He came first 

 prominently into notice while stiU a young man, with his cometary 

 investigations, and his researches into the motions of the planet 

 Mercury, constructing tables by which transits of the latter can be 

 predicted with such absolute correctness that the mean error never 

 exceeds sixteen seconds of time. But it is with the discovery of 

 the planet Neptune that Leverrier's name is imperishably asso- 

 ciated. The case briefly stated was this : — It was found, after a 

 time, that the planet Uranus, discovered by Sir "William Herschel, 

 did not actually follow the orbit which theory had assigned to it. 

 It had a mysterious trick of leaving the computed track, and 

 describing a greater orbit, if the law of gravitation was to hold 

 good, than the tables founded on that law warranted. Astro- 

 nomers were puzzled to account for the vagaries of an orbit that, 

 according to their theory, ought to be well-behaved, and staid and 

 steady-going as any other member of the solar system. What 

 could the perturbations of Uranus mean? was the question asked; 



