526 POPULAR LECTURES AND ADDRESSES. 



added a suggestion, specially interesting to myself, 

 that investigation of periodic variations of latitude 

 may prove to be the best means of determining 

 approximately the rigidity of the earth. As it is 

 we have now, for the first time, what seems to be 

 a quite decisive demonstration of elastic yielding 

 in the earth as a whole, under the influence of a 

 deforming force, whether of centrifugal force round 

 a varying axis, as in the present case, or of tide- 

 generating influences of the sun and moon with 

 reference to which I first raised the question of 

 elastic yielding of the earth's ' material many 

 years ago. 



The present year's great advance in geological 

 dynamics forms the subject of a contribution by 

 Newcomb to the Monthly Notices of the Royal 

 Astronomical Society, of last March. In a later 

 paper, published in the Astronomische NacJiricJitoi, 

 he examines records of many observatories, both 

 of Europe and America, from 1865 to the present 

 time, and finds decisive evidence that from 1865 to 

 1890 the variations of latitude were much less 

 than they have been during the past year, and 



