THE WANDERINGS OF THE NORTH POLE. 83 



been able to get nearer to it than from one end of England to the other. 

 Indeed, as a matter of fact, our knowledge of the movements of the 

 pole are derived from observations made not alone hundreds but even 

 many thousands of miles distant. It is in such observations as those 

 at Greenwich or Berlin, Pulkowa or Washington, that the determina- 

 tions have been made by which changes in the position of the pole can 

 be ascertained with a delicacy and precision for which those would 

 ha»cdly be prepared who were not aware of the refinement of modern 

 astronomical methods. I do not hoAvever imply that the observations 

 conducting" to the discoveries now about to be considered have been 

 exclusively obtained at the observatories I have named. There are a 

 large number of similar institutions over the globe which have been 

 made to bear their testimony. Tens of thousands of different observa- 

 tions have been brought together, and by discussing them it has been 

 found possible to remove a large part of the errors by which such work 

 is necessarily affected, and to elicit from the vast mass those grains of 

 truth which could not have been discovered had it not been for the 

 enormous amount of material that was available. Mr. Chandler has 

 discussed these matters in a remarkable series of papers, and it will be 

 necessary for me now to enter into some little detail, both as regards 

 the kind of observations that have been made, and the results to which 

 astronomers have been thereby conducted. 



Greenwich Observatory lies more than 2,000 miles from the North 

 Pole, and yet if the pole were to shift by as much as the width of 

 Eegent street, the fact that it had done so would be quite perceptible 

 at Greenwich. Let me endeavor to explain how such a measurement 

 could be achieved. In finding the latitude at any locality we desire, 

 of course, to know the distance between the locality and the equator, 

 expressed in angular magnitude. But though this is distinctly the 

 definition of latitude, it docs not at once convey the idea as to how 

 this element can be ascertained. How for instance would an astrono- 

 mer at Greenwich be able to learn the angular distance of the observa- 

 tory from the equator! The equator is not marked on the sky, and it 

 is obvious that the observer must employ a somewhat indirect process 

 to ascertain what he wants. Here, again, we have to invoke the aid 

 of that celestial pole to which I have so often referred. Think of that 

 point on the sky which is the common center of the circles exhibited 

 on Prof. Barnard's photograph. That point is not indeed marked by 

 any special star, but it is completely defined by the circumstance that 

 it is the center of the track performed by the circumpolar stars. We 

 thus obtain a clear idea of this definite point in the sky, and the hori- 

 zon is a perfectly definite line, at all events from any station where 

 the sea is visible. It is not difficult to imagine that by suitable meas- 

 urements we can ascertain the altitude of this point in the heavens 

 above the horizon. That altitude is the latitude of the place; it is, in 

 fact, the very angle which lies between the locality on the earth and 



