266 POPULAR LECTURES AND ADDRESSES. 



we must not, however, infer that the deviations 

 indicated by Peters, Maxwell, and Ncwcomb are 

 unreal. On the contrary, any that fall within the 

 limits of probable error of the observations ought 

 properly to be regarded as real. There is, in fact, 

 a vera causa in the temporary changes of sea-level 

 clue to meteorological causes, chiefly winds, and to 

 meltings of ice in the polar regions and return 

 evaporations, which seems amply sufficient to 

 account for irregular deviations of from .!" to ._,',," 

 of the earth's instantaneous axis from the axis of 

 maximum inertia, or, as I ought rather to say, of 

 the axis of maximum inertia from the instan- 

 taneous axis. 



As for geological upheavals and subsidences, if 

 on a very large scale of area, they must produce, 

 on the period and axis of the earth's rotation, 

 r! frets comparable with those produced by changes 

 of sea-level equal to them in vertical amount. 

 I'W simplicity, calculating as if the earth were of 

 equal density throughout, I find that an upheaval 

 'of all the earth's surface in north latitude and cast 

 longitude and south latitude and west longitude 



