OUR CHIEF TIME-PIECE LOSING TIME. 47 



more slowly, which causes the observed discrepancy. 

 Now it resulted from Laplace's labours as he was 

 the first to announce that the period of the earth's 

 rotation has not varied by one-tenth of a second per 

 century in the last two thousand years. The question 

 thus satisfactorily settled, as was supposed, was shelved 

 for more than a quarter of a century. The result, 

 also, which seemed to flow from the discussion the 

 constancy of the earth's rotation-movement was 

 accepted ; and, as we have seen, our national system 

 of measures was founded upon the assumed constancy 

 of the day's duration. 



But mathematicians were premature in their re- 

 joicings. The question has been brought, by the 

 labours of Professor Adams co-discoverer with Le- 

 verrier of the distant Neptune almost exactly to the 

 point which it occupied a century ago. We are face 

 to face with the very difficulties somewhat modified 

 in extent, but not in character which puzzled Halley, 

 Euler, and Lagrange. It would be an injustice to 

 the memory of Laplace to say that his labours were 

 thrown away. The explanation offered by him is 

 indeed a just one, but it is insufficient. Properly esti- 

 mated, it removes only half the difficulty which had 

 perplexed mathematicians. It would be quite impos- 

 sible to present in brief space, and in form suited to 

 these pages, the views propounded by Adams. What, 

 for instance, would most of our readers learn if we 

 were to tell them that, ( when the variability of the 

 eccentricity is taken into account, in integrating the 



