NO. 8.] REMARKS ON THE EARTH'S CRUST. 85 
of force are obliged to turn back towards the oceans again, und that 
more rapidly than they had turned in under the continent. On account of 
the inconsiderable depth of the oceans as compared with the thickness of the 
earth’s crust, however, this turning back is not so complete as to cause a 
regular distribution of the lines of force over the outer surface of the earth. 
The lines of force will therefore be crowded rather more closely together on 
the continents, along their boundary or towards the coast-line; while immedi- 
ately outside this, on the ocean, they will lie farther from one another than 
the normal distance. An endeavour to illustrate these conditions is made in 
the accompanying figure. 
If we now consider a tube of force issuing from the outer surface, and 
terminating in one of the surface-elements into which we have imagined the 
surface of the inner nucleus to be divided, it is evident, since the lines of 
force, according to the above, lie somewhat closer together than normally 
just within the coast-line of a continent, that this tube of force will cut 
off from the free surface an element somewhat smaller than it would have 
been had the lines of force been normally distributed over the free surface, 
and the acceleration been normal in consequence. The reverse will be the 
case if the tube of force intersects the free surface somewhat beyond the 
coast-line out on the ocean. According to our explanation on page 69, the direct 
consequence of this will be that the acceleration must be rather greater than 
normal on the continents in the neighbourhood of the coast-line, and somewhat 
less than normal out on the ocean a little beyond the shore, as we have 
demonstrated above. 
We have assumed above that on an average there are equally large 
masses over equal elements of the surface of the inner nucleus. If we imagine 
that there is an equilibrium of pressure upon this from the outer crust, the 
result arrived at above will not be altered in any degree worth mentioning. 
In order to satisfy this new condition, we need only, as regards the continents, 
add at sea-level a stratum of rock about 50 m. thick, to the masses we have 
considered above. 
As regards the oceanic islands, the increased attraction on them is easily 
explained, whether we imagine the masses of which they are formed to repre- 
sent actual surplus mass, or assume — which seems the more reasonable — 
