20 MAGNITUDE, FIGURE, AND 



mobile notwithstanding the great pressure to which they 

 are subject, may cause internal displacements of mass, which 

 may modify, after very long intervals of time, the geometric 

 surface itself in the curvature of the meridians and parallels 

 within small distances; while the physical surface is ex- 

 posed, in its oceanic portion, to a constantly recurring 

 periodical displacement of mass by the ebb and flow of the 

 tides. The smallness of the effect on gravitation of the 

 first-named supposed class of phsenomena, may cause a very 

 slow and gradual change taking place in continental regions 

 to escape discovery by actual observation : according to 

 EesseFs calculation, in order to increase the height of the 

 pole at any particular place only 1", there must be supposed 

 to be displaced in the interior of the earth a mass of such 

 weight as that, its density being taken as equal to the mean 

 density of the earth, its bulk shall be equal to 114 cubic 

 geographical (German) miles. (German geographical miles 

 are 15 to a degree). ( 5 ) Large as this volume may appear 

 for the supposed displaced mass when we compare it with 

 the volume of Mont Blanc, of Chimborazo, of Kinchinjunga, 

 it will seem less so when we recollect that the terrestrial 

 spheroid contains above 2650 millions of such cubic 

 miles. 



The problem of the figure of the Earth the connection of 

 which with the geological question respecting an earlier fluid 

 state of the rotating planetary body had already been recog- 

 nised at the great epoch ( 6 ) of Newton, Huygens, and Hooke, 

 has been attempted to be solved, with unequal success, in 

 three different ways : by astro-geodesical measurement of 

 degrees, by pendulum experiments, and by the inequalities 

 of the Moon in latitude and longitude. The first method 



