354 SCHLESINGER— VARIATIONS OF LATITUDE. [April 24, 



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

 the reason for estabhshing 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. When 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, Massachusetts, who 

 took the lead in investigating the nature of latitude variations. By 

 overhauling ancient observations (made of course without any ref- 

 erence to the present subject) he was able to trace the presence of 

 the variations 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 miscel- 

 laneous series of observations and thus to set down a tolerably con- 

 tinuous record of the variations during a century and a half. How- 

 ever interesting a fact this may be from an historical point of view, 

 it does not help very much in a practical study of the subject. 

 There are two reasons for this : first, it is only for European sta- 

 tions (and for the most part only for Greenwich) that we have any 

 knowledge of these earlier variations ; the other component of the 

 wanderings of the pole, namely that in the meridian at right angles 

 to the meridian of Greenwich, did not begin to be known until very 

 recently. Again, these ancient observations were undertaken for 



