566 



SCIENCE. 



[N. S. Vol. I. No. 21. 



This would indicate that from Aiigust to 

 November, 1884, the pole of the earth had 

 approached Berlin more closely by 20 to 30 

 feet than in the time from March to May. 



This conclusion was fortified by the ex- 

 amination of other data, obtained from the 

 observations made at Pulkova by Nyren. 



Here, then, was evidence of a compara- 

 tively rapid change in latitude. New ob- 

 servations were undertaken at Berlin, Pots- 

 dam, Prague, and Bethlehem, Penn. (all by 

 Talcott's method), and all agreed in show- 

 ing plus and minus changes in latitude for 

 the years 1888-'90. 



There were still some doubters. More- 

 over it was decided to critically test the 

 matter bj^ sending an expedition to the 

 Sandwich Islands, which is 180 degrees 

 (nearly) in longitude from Berlin. If it 

 was known the latitude of Berlin increased, 

 then a point in the northern hemisphere 180 

 degrees away from Berlin should simul- 

 taneously show a decrease in latitude, for if 

 the pole moves toward Berlin it must move 

 from the point on the other side of the earth. 



Our own Government joined in the effort. 

 Marcuse of Berlin and Preston of Wash- 

 ington spent more than a year on the Sand- 

 wich Islands observing for latitude, while 

 at the same time observations were con- 

 tinued at Berlin, Prague and Strassbui'g in 

 Europe, and at Eockville, Bethlehem and 

 San Francisco in the United States. The 

 results of all these observations have been 

 published, and show, without a chance of 

 error, that the earth's axis is moving, that 

 the latitudes at the Sandwhich Islands in- 

 creased when the latitudes in Germany di- 

 minished and vice versa. 



The law of the change was eagerly and 

 industriously sought for by some of the 

 ablest mathematical astronomers of the 

 world. They first worked on the idea that 

 the changes must conform to the 305-day 

 period of Euler, combined with _ an annual 

 change due to causes set forth by Sir W. 



Thoinson. and which I have previously men- 

 tioned. None of these investigations have 

 given a satisfactory formula for the predic-"^ 

 tion of the latitude of any place. 



In 1891 Dr. S. C. Chandler, of Cambridge, 

 Mass., began his investigation of the prob- 

 lem. He remarks : 



" I deliberately put aside all teaching of 

 theorj', 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 exis- 

 tence of the Eulerian period (of 305 days) 

 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. The problem which I therefore 

 proposed to myself was to see whether it 

 would not be possible to lay the numerous 

 ghosts in the shape of various discordant, 

 residual phenomena pertaining to determi- 

 nations of aberration, parallaxes, latitudes 

 and the like, which have heretofore flitted 

 elusively about the astronomy of precision 

 during the century, or to reduce them to 

 some tangible form by some simple consis- 

 tent hypothesis. It was thought that if 

 this could be done a study of the nature of 

 the forces as thus indicated, by which the 

 earth's rotation is influenced, might tend to 

 a phj'-sical explanation of them." 



Dr. Chandler proceeded to examine his 

 own work with the Almucantar at Cam- 

 bridge, the observations of Ktistner, Gyld^n, 

 Nyi-6n, the Washington observations and 

 others. He found that they all seemed to in- 

 dicate that the pole of the rotation axis was 

 moving from west to east about the axis of 

 figure of the earth in a period of 427 days. 

 Other observations did not seem to confirm 

 this period. Finally he made an elaborate 

 analysis of 33,000 observations between 1837 

 and 1891, and the result was an empirical 

 law which can be announced as follows : 



