478 



SCIENCE. 



[N. S. Vol. I. No. 18. 



We could take a solid bodj^, pass an axis 

 through it in any direction, and make it 

 rotate on that axis. 



It was shown by Euler, more than a cen- 

 tury ago, that if a solid body rotated on an 

 axis dififerent from that of figure, the posi- 

 tion of the axis of rotation in the bodj' 

 would be subject to a slow change, consist- 

 ing iu a constant revolution around the axis 

 of figure. Were this body the earth, the 

 latitude of a place, as determined bj^ astro- 

 nomical observation, would change in the 

 same way. The time of one revolution of 

 the pole would depend upon the figure of 

 the earth. The flattening of the earth is 

 such that, were it a perfectly rigid body, the 

 time of revolution would be about 305 days; 

 that is to say, the north pole would make 

 its circuit in a period of 305 days. 



There being no necessity that the two 

 poles should coincide, the question was 

 naturally raised whether, perhaps, there 

 might actually be such a difference of the 

 two poles, and, in consequence, a change of 

 latitude of every place on the earth's sur- 

 face having a period of 305 days. The first to 

 investigate this qu.estion with all the refine- 

 ments of modern astronomy was C. A. F. 

 Peters, who, half a century ago, was an as- 

 sistant at the Pulkowa Observatory. In 

 his classic paper on the parallax of the fixed 

 stars, one section is devoted to the qiiestion 

 of the variabilitj' of the latitude in a period 

 of 304 days, which, according to the then 

 accepted value of the flattening of the earth, 

 would be the time of one revolution of the 

 poles. He found a coefiicient of 0".079, 

 with a probable error of 0".017. This re- 

 sult was so extremely minute that it might 

 have arisen from unavoidable sources of er- 

 ror; and the conclusion therefore reached 

 was that if there was anj^ such separation of 

 the two poles, it was too small to be certainly 

 detected by the most refined observations. 



In 1862 our late fellow member, Profes- 

 sor Hubbard, of the ITaval Observatory, 



commenced a series of observations with 

 the prime-vertical ti'ansit of that institu- 

 tion, which would be available for the same 

 research. They were interrupted after a ~ 

 little more than a year, by his untimelj' 

 death, but were continued four years longer 

 by Ms successors. The result was the same 

 as that reached by Peters ; no change hav- 

 ing a period of 305 days could be detected. 



In 1873 the question was investigated by 

 Nj-ren in connection with a longer series of 

 observations on the latitude of the Pulkowa 

 Observatory. His results were somewhat dis- 

 cordant, and the only conclusion that could 

 be drawn fi-om them was that the variation 

 could not be certainlj-- detected by these 

 most refined observations. 



Ten years later Nyren repeated the de- 

 termination, in connection with his obser- 

 vations for the determination of the con- 

 stant of abberation. These observations, 

 made with the prime-vertical transit, were 

 carried through with the minutest attention, 

 and the utmost care to avoid everj^ con- 

 ceivable source of error. Curious discord- 

 ances were nevertheless found in the re- 

 sults for the constant of abberation. 



In 1885 Kiistner showed that they could 

 be accounted for by supposing a change 

 going on in the latitude. But nothing 

 could be inferred respecting the law or the 

 cause of the change. 



As a result of these investigations, the 

 coincidence of the earth's axes of rotation 

 and of figure has, until within a verj' few 

 years, been assumed bj^ astronomers as a 

 practicalljr established fact ; and all their 

 methods of observation have rested upon 

 the idea of absolute coincidence. This con- 

 fidence has not been disturbed until within 

 a few years, when the question has been 

 reopened. But it has now apparently been 

 settled upon a new and firmly established 

 basis. 



Dr. Chandler's work upon this subject 

 began with observations made by him in 



