1916] on The Movements of the Earth's Pole 675 



however, quite obvious to Cliandler that his series of observations 

 contained no warrant for an Eulerian period of ten months and he 

 therefore, to quote his own words, " deUberatelj put aside all 

 teachino:s of theory, because it seemed to me high time that the facts 

 should be examined by a purely inductive process ; that the nugatory 

 results of all attempts to detect the existence of the Eulerian period 

 probably arose from a defect of the theory itself, and that the 

 entangled condition of the whole subject required that it should be 

 examined afresh by processes unfettered by any preconceived notions 

 whatever." This bold rejection of theory and"^ appeal to observation 

 alone was rewarded with immediate success, and Chandler was able 

 to show that his observations of 1884-5 contained unmistakable 

 evidence of the rotation of the one pole about the other in a period 

 of not 305 days, but 428 days. Wherein, then, lay the deficiency of 

 Euler's investigation ? As already hinted this arose from the assump- 

 tion of rigidity and it was shown first by Newcomb and afterwards, 

 more completely, by Hough, that the 428 day period was fully in 

 accord with a degree of elastic yielding of the earth quite consonant 

 with probability. Hough showed that if the earth were as rigid as 

 steel the period would become 440 days ; that the actual period is 

 somewhat shorter than this means that the earth as a whole is 

 decidedly more rigid than steel, a result which accords perfectly with 

 other known phenomena which depend upon the earth's elasticity, 

 such as the rate of propagation of earthquake waves. 



Immediately following on this initial success Chandler undertook 

 a prolonged and most laborious examination of old observations and 

 reached results which have not completely borne the test of subse- 

 quent review\ He was confident that the whole movement of the 

 pole might be explained as the superposition of two rotations, one 

 circular with a 428 day period and one eUiptical with a period of a 

 year. He thought, further, that there was evidence that the longer 

 period had varied in past times and that in 1770 it was less than a 

 year. This last result was traversed by Newcomb, who showed its 

 extreme improbability. While fully bearing in mind the lessons of 

 past experience as to the unwisdom of relying too closely upon pure 

 theory, we cannot resist the conclusion that to accept any large 

 change in the 428 day period within recent years would be to set 

 aside the whole dynamical justification for accepting this period as a 

 reality, it being quite impossible to admit that the elastic constants 

 of the earth can be subject to any appreciable alteration within such 

 time as a century or so. 



As regards an annual period we should now prefer to say that, 

 while there are doubtless seasonal transfers of material upon the 

 earth, such as the accumulation and melting of arctic ice, w^hich may 

 produce a movement of the pole with an approach to a yearly 

 periodicity, the part of the movement due to a true annual period is 

 very small and is quite masked by large irregular disturbances. We 



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