250 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1916. 



But the first clear word to this effect came in 1888 from the lips of 

 Kiistner, at Berlin. He had invented and applied a method for deter- 

 mining the amount of the aberration of light; but he found that his 

 observations gave well nigh impossible resoilts, agreeing neither 

 among themselves nor with earlier reliable observations. By a nice 

 chain of logic he was able to exclude one possible explanation after 

 another until there was left only the supposition that the latitude of 

 his station had changed while his obsexvations were in progress. 

 Next he examined nearly contemporaneous observations made at 

 other places, and when he found that he could account for certain 

 puzzling discrepancies he no longer hesitated to announce that lati- 

 tudes were variable after all. 



This announcement awoke the liveliest interest and encountered 

 no little skepticism. Special observations were at once set on foot 

 at various observatories in Europe and America, as well as at a 

 station near Honolulu in the Sandwich Islands. These islands are 

 about opposite in longitude to the European stations, and this was 

 the reason for establishing a station there. For obviously if the 

 pole is really changing its place, then the changes in latitude for two 

 opposite stations will be the reverse of each other. T\nien in 1893 

 this was found actually to be the case, other possible explanations 

 for the observed phenomena at once fell down, and latitude varia- 

 tions became for the first time a universally accepted fact. 



Much time and effort have since been expended in attempting to 

 formulate the " laws " of latitude variations and to give them a 

 mechanical interpretation. But observation has shown that the 

 variations are of unexpected complicity, and as a consequence we 

 are still very far from having satisfactory knowledge of this subject. 

 By the same token it is probable that an intensive study of these 

 variations, particularly from points of view other than the astro- 

 nomical, will teach us much concerning the interior of the earth as 

 well as some of its surface phenomena. 



It was the late Dr. Chandler, of Cambridge, Mass., who took the 

 lead in investigating the nature of latitude variations. By over- 

 hauling ancient observations (made of course without any reference 

 to the present subject) he was able to trace the presence of the varia- 

 tions back to the time of Bradley in the middle of the eighteenth 

 century. Thus it happens that at the very time that Euler was 

 writing the first theoretical paper on the subject, Bradley had already 

 begun making the observations from which the actual existence of 

 latitude variations might have been proven at once. Chandler was 

 able to gather similar evidence from other miscellaneous series of 

 observations and thus to set down a tolerably continuous record of 

 the variations during a century and a half. However interesting a 

 fact this may be from an historical point of view, it does not help 



