A436 TRANSACTIONS OF SECTION A. 
I showed before a smoothed curve (fig. 3) which I proposed to take as representing 
the facts to be accounted for. The resemblance of the two curves seems to be 
striking. Incidentally it has been noticed how the prominent features of the 
distribution of continent and ocean are associated with the presence of various 
harmonics. As regards the contour of the great ocean basins, we seem to be 
justified in saying that the earth is approximately an oblate spheroid, but more 
nearly an ellipsoid with three unequal axes, having its surface furrowed according 
to the formula for a certain spherical harmonic of the third degree, and displaced 
relatively to the geoid towards the direction of the Crimea. 
As regards the amount of elevation and depression in different parts, the 
agreement of the theory with the facts is not so good. The computed elevation is 
too small in Southern Africa, Brazil, and the southern part of South America, 
too great in the Arctic regions, to the south of Australasia, and in the Mediter- 
ranean region. There are many reasons why we could not expect the agreement 
to be very good. One is the roughness of the method of harmonic analysis that 
was used. But there is also the fact that many causes must have contributed to 
the shaping of our actual continents and oceans besides those which have been 
taken into account in the theory. It appears, however, that the broad general 
features of the distribution of continent and ocean can be regarded as the conse- 
quences of simple causes of a dynamical character: eccentric position of the centre 
of gravity, arising from a past state of inadequate resistance to compression, an ~ 
inherited tendency, so to speak, to an ellipsoidal figure, associated with the 
Ocean 
Ocean 
Fig. 14. 
attraction of the moon in a bygone age, the rotation, and the interactions of these 
various causes. 
In attempting to estimate the bearing of the theory on geological history we 
must be guided by two considerations. The first is that the earth is not now 
eravitationally unstable. From observations of the propagation of earthquake 
shocks to great distances, we can determine the average resistance to compression, 
and we find that this resistance is now sufficiently great to keep in check any 
tendency to gravitational instability. The eccentric position of the centre of 
gravity must be regarded as a survival from a past state in which the resistance 
to compression was not nearly so great as it is now. The second guiding con- 
sideration is that, according to the theory, the inequalities which are expressed by 
spherical harmonics of the third degree are secondary effects due to the interaction 
of the causes which give rise to inequalities expressed by harmonics of the first 
and second degrees. We should expect, therefore, that the inequalities of the 
third degree would be much smaller than those of the first and second degrees ; 
but the harmonic analysis shows that the three inequalities are entirely comparable, 
We must conclude that the harmonics of the first and second degrees which we 
can now discover by the analysis are survivals from a past state, in which such 
inequalities were relatively more important than they are now. Both these con- 
siderations point in the same direction, and they lead us to infer that certain 
secular changes may have taken place in the past, and may still be going on. 
Sixty-nine years ago Charles Darwin wrote: ‘The form of the fluid surface of the 
nucleus of the earth is subject to some change the cause of which is entirely 
