278 VARIATION OF LATITUDE. 



to indicate that the pole of the rotation axis was moving from west to 

 east about the axis of figure of the earth in a iieriod 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 : 



The pole of the rotation axis of the earth moved with its greatest 

 velocity about the pole of the axis of figure about the year 1774; the 

 period then was 348 days. The velocity has diminislied with an accel- 

 erated rate since then. In 1890 the period was 443 days. The distance 

 of one pole from the other was about 22 feet, equal to 0.22". 



Further elaborate examination of this material developed the exceed- 

 ingly important and interesting result that the changes in latitude 

 were the sum of two periodic fluctuations superposed on. each other. 

 One had a period of about 427 days and an amplitude of 0.12"; the 

 second had a period of a year, with an amplitude that was variable 

 between 0.04" and 0.20". 



Sometimes these two fluctuations worked together, giving a total 

 range of 0.33", and at times they conspired against each other, reduc- 

 ing the range to a mininuim of a few hundredths of a second. He 

 compared his theory with the observations, and the result was, in the 

 main, exceedingly satisfactory. 



His conclusions were attacked as to the 427-day term. The annual 

 term could be explained as due to meteorologic causes. 



Professor New comb, however, in March, 1892, explained, in a paper 

 communicated to the Monthly Notices of the Eoyal Astronomical 

 Society, that in deducting the Eulerian i)eriod of 305 days the earth, as 

 we have remarked, was considered absolutely rigid; that- when the 

 eflect of the mobility of the oceans and of the lack of perfect rigidity 

 of the earth were taken into account, the mathematics reijuired a time 

 of rotation of the true pole about the axis of figure longer than the 

 previously accepted 305 days. Making certain assumptions, Newcomb 

 obtained a period of 443 daj'S.' 



An additional interesting conclusion which Dr. Chandler has lately 

 jmblished is that the fluctuation with a period of 427-428 days is a cir- 

 cular one, as theory seems to demand, while the annual fiuetuations 

 appear elliptical in character. 



An exceedingly interesting and important confirmation of the Chand- 

 lerian i>eriod of 427 days, or about 14 months, was lately announced by 

 M. Tisserand. Examination has been made of the tide records of the 

 Helder in Holland. These are kept with great accuracy. It has been 

 found that between 1851 and 1893 these tide records show a variation 

 in the average sea level indicating a 14-month period. The greatest 



'Prof. R. S. Woodward has lately obtained, by a new discussion of the theoretical 

 l>roblem, a formula that seems to indicate the correctness of Chandler's empirical 

 formula. 



