446 GEORGE B1DDELL AIRY. 



power displayed in the researches from which these predictions re- 

 sulted, or of their deserved prominence in the history of astronomy. 



Among the various researches which were subsequently undertaken 

 by Adams, that relating to the secular variation of the Moon's mean 

 motion was perhaps the most interesting and importaut. This in- 

 vestigation reopened a question which had been regarded as finally 

 settled by Laplace. Adams detected an omission in the work of his 

 predecessor, which, when supplied, proved to disturb the agreement 

 previously supposed to exist between theory and observation. A new 

 physical cause was now required to explain the observed results, and 

 this was found in the retardation of the rotation of the Earth due to 

 the tides. In this case, a protracted discussion of the subject among 

 the foremost mathematicians who concerned themselves with astronom- 

 ical inquiries resulted in confirming the theory maintained by Adams. 

 But the amount of the secular variation forming the original subject of 

 discussion has not yet been definitely fixed by observation. At present 

 it seems probable that the researches of Adams brought theory into 

 better accordance with fact, instead of disturbing an existing agreement. 

 If this view should prevail, tidal retardation must be regarded as com- 

 pensated by terrestrial contraction, or by causes as yet unknown. 



The orbit of the remarkable body of meteors to which is due the 

 recurrence of brilliant displays of shooting stars about the middle of 

 November, three times in each century, was another subject investi- 

 gated by Adams with great success. In general, it may be said that in 

 all the principal discussions of his time respecting recondite questions 

 of theoretical astronomy he took a prominent part, and that no argu- 

 ments were regarded with more respect than his by those capable of 

 appreciating them. 



Besides his academical honors, he received many tokens of distinction 

 from learned societies, and his name was familiar, as it will long con- 

 tinue to be, wherever the mechanism of the solar system is discussed 

 or studied. 



GEORGE BIDDELL AIRY. 



George Biddell Airy was born at Alnwick, England, July 27, 

 1801. His university education was obtained at Cambridge, where his 

 mathematical ability became conspicuous, and where he graduated as 

 Senior Wrangler in 1823. In the following year he was elected a 

 Fellow of Trinity College ; in 1826 he was made a Professor, and in 

 1828 the Director of the Observatory. These early honors were 



