I9I5.] SCHLESINGER— VARIATIONS OF LATITUDE. 353 



We must understand that it is only in our time and only after the 

 lapse of many years since Euler published his memoir, that latitude 

 variations have actually been observed. There was nothing in 

 Euler's theory to indicate how large a variation to look for, since 

 this is a matter that depends upon the whole complex of " initial 

 conditions," of which our knowledge is the very vaguest. But this 

 theory does tell us what the period of the variation should be, since 

 this depends upon the shape of the earth and the distribution of 

 the material within it, and precisely the information that is here 

 needed is afforded by a study of precession. Applying this infor- 

 mation Euler was able to say that the period of the latitude varia- 

 tion should be ten months. Bessel at Konigsberg in 1842, later 

 Peters at Pulkova, Nyren also at Pulkova, Downing at Greenwich, 

 and Newcomb at Washington, all searched their observations for 

 evidence of a latitude variation having a period of ten months, but 

 all in vain. Astronomers concluded that if latitude variations 

 existed at all, their extent was too small to be detected by instru- 

 ments of the precision that had then been attained. 



Toward the end of the nineteenth century vague whisperings 

 that this conclusion might be incorrect seem to have been in the air. 

 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 de- 

 termining the amount of the aberration of light ; but he found that 

 his observations gave well-nigh impossible results, 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 observations 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 scepticism. Special observations were at once set on foot 

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

 tion near Honolulu in the Sandwich Islands. These islands are 



