May 21, 1895.] 



SCIENCE. 



567 



The pole of the rotation axis of the earth 

 moved witli its greatest velocitj* about the 

 pole of the axis of figure about the year 

 1774 ; the period then was 34S days. The 

 velocity has diminished with an accelerated 

 rate since then. In 1890 the period was 

 443 days. The distance of one pole from 

 the other was about 2'2 feet = 0.22". 



Further elaborate examination of this 

 material developed the exceedingly impor- 

 tant and interesting result that the changes 

 in latitude were the sum of two jyeriodic fluc- 

 tuations superposed on each other. One had 

 a period of about 427 days and an ampli- 

 tude of 0.12" The second had a period of 

 a year -wdth an amplitude that was variable 

 between .04" and .20" 



Sometimes these two fluctuations worked 

 together, giving a total range of .33", and 

 at times they conspired against each other, 

 reducing the range to a minimum 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 terra. The annual term could be 

 explained as due to meteorologic causes. 



Professor Newcomb, however, in March, 

 1802, explained in a paper communicated 

 to the Monthly Notices of the Royal Astro- 

 nomical Society that in deducing the Eu- 

 lerian period of 30.5 days the earth, as we 

 have remarked, was considered absolutely 

 rigid ; that when the efi"ect of the mobility 

 of the oceans and of the lack of perfect rig- 

 idity of the earth were taken into account, 

 the mathematics required a time of rotation 

 of tlie true pole about the axis of figure 

 longer than the previously accepted 30.5 

 days. Making certain assumptions New- 

 comb obtained a period of 443 daj's.* 



An additional interesting conclusion 



* Professor R. S. Woodward ha.s lately ohfciined In- 

 a new discussion of the theoretical prol)leni a formula 

 that seems to indicate the correctness of Chandler's 

 empirical formula. 



which Dr. Chandler has lately published is 

 that the fluctuation witli a period of 427- 

 428 daj's is a circular one, as theory seems 

 to demand, while the annual fluctuations 

 appear elliptical in character. 



An exceeilingly interesting and important 

 confirmation of the Chandlerian period 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 be- 

 tween 1851 and 1893 these tide records 

 show a variation in the average sea level 

 indicating a 14-month period. The greatest 

 divergencies are very small, onlj- 14 mm.= 

 i inch about, l)ut they appear unmistakably 

 and are what theory would demand. 



In a letter recently received from Dr. 

 Chandler he states that he finds that the 

 annual part of the polar motion is an ellipse 

 three or four times as long as broad, and 

 he expresses the law of the motion of the 

 pole in this ellipse as that the areas de- 

 scribed from the centre are proportional to 

 the times. 



We can conclude safely, therefore, that 

 no large changes of latitude have taken 

 place for many thousands of years ; in 

 fact, in geologic times, that there is no 

 adequate proof of prog ress ire changes in the 

 latitude of any place ; but finally that very 

 small periodic changes have occurred, and 

 they are such as can be and are oljserved. 



The feeling is growing in the minds of 

 those who have given the subject close at- 

 tention that we shall find that many and 

 various causes enter into the problem of 

 determining the law of changes. It will, no 

 doubt, take many years of ciireful observa- 

 tion to obtain the data necessary to fully 

 test Dr. Chandler's or any other hyix)thesis. 



The scientific men abroad are discussing 

 the advisability of establishing several ob- 

 servatories at various places on the earth's 

 surface, for the purpose of collecting the data. 



