SHIFTING OF THE EARTH'S AXIS 419 



minute changes of latitude were taking place, but it is only during the 

 last quarter century that the methods of observation and calculation 

 have reached that degree of refinement necessary to detect these small 

 changes. 



In 1884 and 1885 Dr. Kiistner, astronomer at the Eoyal Observatory 

 of Berlin, made a series of observations upon certain stars for the pur- 

 pose of determining the constant of aberration — the maximum apparent 

 displacement of a star due to the finite ratio between the speed of the 

 earth in its orbit and the velocity of light. One of the quantities used 

 in the reduction of these observations is the latitude of the place of 

 observation. Dr. Kiistner found his results to be discordant, much 

 more so than he had good reason to believe that they should be from 

 the known care and precision with which the observations were made. 

 Upon investigation it was found that these discrepancies could be 

 almost entirely explained away by assuming a change in the latitude. 

 Dr. Kiistner, therefore, in 1888, made the bold announcement that the 

 latitude of the Berlin Observatory had changed during the period over 

 which his observations extended. 



This announcement aroused wide-spread interest and steps were 

 immediately taken by the International Geodetic Association 1 to test 

 the reality of the announced variation. Through the cooperation of 

 the observatories at Berlin, Potsdam, Prague and Strassburg, observa- 

 tions for latitude were begun in 1889 and carried on continuously for 

 over a year. These observations agreed in showing a minute but appre- 

 ciable change in the latitude. In order to test the matter still further, 

 an expedition was sent in 1891-2 to Honolulu, and observations for 

 latitude were made there simultaneously with others made at the 

 observatories just named. As Honolulu is on the opposite side of the 

 earth from Europe, it is seen at once, from Fig. 1, that if the latitude 

 were increasing at the European observatories a corresponding decrease 

 should be shown at the Honolulu station. The results came out as 

 expected and this was generally accepted as a complete demonstration 

 of the reality of this phenomenon. Fig. 2 gives a graphical representa- 

 tion of the results, time being measured along the horizontal and lati- 

 tude along the vertical line. 



The observations thus far made showed that the changes in latitude 

 were periodic in character, that is, the latitude of, any place would 

 increase for a certain length of time and then decrease to a minimum 

 value and so on, continuing to oscillate between certain limits. It is 

 easily seen that such changes in the latitude of any place may be 



1 The International Geodetic Association has its headquarters at Potsdam, 

 Germany, and is supported by the principal governments of Europe, the United 

 States, the Argentine Republic and Japan. It carries out pieces of geodetic and 

 astronomical work which are international in their scope. 



