504 POPULAR LECTURES AND ADDRESSES. 



demonstration that motion, relatively to the 

 Earth, of the Earth's instantaneous axis of 

 rotation, is the cause of variations of latitude 

 which had been observed in Berlin, Greenwich, 

 and other great observatories, and which could 

 not be wholly attributed to errors of observation. 

 This, Professor Foerster remarks, gives observa- 

 tional proof of a dynamical conclusion contained 

 in my Presidential Address to Section A of the 

 British Association, at Glasgow, in 1876, to the 

 effect that irregular movements of the Earth's 

 axis to the extent of half a second may be 

 produced by the temporary changes of sea-level 

 due to meteorological causes. 



It is proposed that four permanent stations for 

 regular and continued observation of latitude, at 

 places of approximately equal latitude and on 

 meridians approximately 90 'apart, should be 

 established under the auspices of the International 

 Geodetic Union. The reason for this is that a 

 change in the instantaneous axis of rotation in 

 the direction perpendicular to the meridian of 

 any one place would not alter its latitude, but 



