262 POPULAR LECTURES AND ADDRESSES. 



Royal Society, seem to show possibly no sensible 

 yielding, or perhaps more probably some degree of 

 yielding, of the earth's figure. The absence from 

 all the results of any indication of a l8'6 yearly 

 tide (according to the same law as the other long- 

 period tides) is not easily explained without 

 assuming or admitting a considerable degree of 

 yielding. 



Closely connected with the question of the 

 earth's rigidity, and of as great scientific interest 

 and of even greater practical moment, is the 

 question, How nearly accurate is the earth as a 

 timekeeper? and another of, at all events, equal 

 scientific interest, How about the permanence of 

 the earth's axis of rotation ? 



Peters and Maxwell, about 35 and 25 years ago, 

 irately raised the question, How much does the 

 earth's axis of rotation deviate from being a prin- 

 cipal axis of inertia ? and pointed out that an 

 answer lo this question is to be obtained by 

 looking for a variation in latitude of any or every 

 place on the earth's surface in a period of 306 

 days. The model before you illustrates the 



