PRESIDENTIAL ADDRESSES. 525 



latitude in each case. This is just what would 

 result from motion of the north and south polar 

 ends of the earth's instantaneous axis of rotation, 

 in circles on the earth's surface of 7-5 metres 

 radius, at the rate of once round in 385 days. 



Some time previously it had been found by Mr. 

 S. C. Chandler that the irregular variations of 

 latitude which had been discovered in different 

 observatories during the last fifteen years seemed 

 to follow a period of about 427 days, instead of 

 the 306 days given by Peters' and Maxwell's 

 dynamical theory-, on the supposition of the earth 

 being wholly a rigid body. And now, the German 

 observations, although not giving so long a period 

 as Chandler's, quite confirm the result that, what- 

 ever approximation to following a period there is, in 

 the variations of latitude, it is a period largely 

 exceeding the old estimate of 306 days. 



Newcomb, in a letter which I received from him 

 last December, gave, what seems to me to be, 

 undoubtedly, the true explanation of this apparent 

 discrepance from dynamical theory, attributing it 

 elastic yielding of the earth as a whole, He 



