May io, 1896.] 



SCIENCE. 



725 



and at Bethleliem, Eockville and San Fran- 

 cisco, 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 lati- 

 tudes at the Sandwich Islands increased 

 whea the latitudes in Germany diminished 

 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. 

 Thompson. None of these investigations 

 gave any satisfactory formulas for the predic- 

 tion of the latitude of a place. In 1 89 1 Dr. S. 

 C. Chandler of Cambridge, Mass., began his 

 investigations of the problem. He remarks : 



" I deliberately put aside all teaching 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 exis- 

 tence of the Eulerian period (of 305 days) 

 probably arose from a defect in 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 my- 

 self was to see whether it would not be 

 possible to lay the numerous ghosts in the 

 shape of the various discordant, residual 

 phenomena pertaining to determinations of 

 aberration, parallaxes, latitudes and the like, 

 which have heretofore flitted elusively about 

 the asti'onomy of precision during the cen- 

 tury ; or to reduce them to some tangible 

 form by some simple, consistent hypothesis. 

 ^ ^ ^ It was thought that if this could be 

 done, a study of the nature of the forces are 

 thus indicated, by which the earth's rota- 

 tion is influenced, might tend to a physical 

 explanation of them." 



Dr. Chandler examined a great mass of 

 observations, new and old, and from their 

 discussion has obtained a formula which at 

 the present time expresses very well the 

 changes of latitude at any place at any 

 1 epoch. For his excellent and laborious 

 work of several years, Dr. Chandler has re- 

 ceived medals from our National Academy 

 and the Eoyal Astronomical Society of 

 London. 



The result of Dr. Chandler's investiga- 

 tion show that the pole of the axis of rota- 

 tion of the earth may be considered as re- 

 volving from west to east in a circle with a 

 radius of about 14 feet, with an average 

 period of 428.6 days. The center of this 

 circle moves from west to east around the 

 circumference of an ellipse in about a year. 

 The pole of the axis of figure is at the cen- 

 ter of this ellipse. Evidences of still 

 greater complexity in the motion of the 

 pole seem to be exhibited by Dr. Chandler's 

 analysis. These motions combining make 

 the actual path of the pole sometimes the 

 arc of an ellipse, at times a circular arc and 

 then again almost a straight line. At 

 times the various changes conspire to give 

 a maximum of ".33, and at others the 

 minimum separation of few hundredths of a 

 second of the pole of rotation from the pole 

 of figure. 



During the year 1895 Chandler's formula 

 makes the pole move nearly parallel witk 

 our meridian. This would produce observ- 

 able changes of latitude here, but none at- 

 places 90 degrees east (in Europe) or west 

 of us. To thoroughly test the formula ob- 

 servations must be kept up for many years 

 at various places on the earth's surface. 



The International Geodetic Association 

 propose the establishment of four observa- 

 tories on the same parallel of latitude: in 

 Japan, Sicily, Virginia and California. At 

 these places it is suggested that photo- 

 graphic observations be kept up for many 

 years, so that more exact data can be ob- 



