PRESIDENTIAL ADDRESS. A433 
fig. 7. The equatorial regions of elevation given by the analysis are near the ends 
of a diameter, as we should expect. ; 
It has not been necessary to enter into a minute description of the harmonics of 
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the first and second degrees, because*they-represent very simple things—a shifting 
of the surface to one side and a distortion of it into an ellipsoid. The harmonics 
of the third degree arefnot so familiar.&There are essentially four of them, each 
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Fig.8. 
specifying a standard pattern of deformation. ‘The first of these, the zonal 
harmonic, gives us a division of the surface into two polar caps and two zones by 
means of the equator and the parallels of latitude about 51° north and 51° south. 
Fia.9. 
Alternate zones are depressed and elevated, as shown in fig. 8. The existence of 
an Antarctic continent and an Arctic Ocean is specially associated with the 
presence of this harmonic, and the disproportion of the continental areas in the 
1907. FF 
