28 WILLIAM H. PICKERING 
An inspection of this figure shows that the Earth’s center of grav- 
ity, which is the center of the circular arcs, does not coincide with 
its center of volume, and this deviation would be still more marked 
were the mobile portions of the surface—i. e., the oceans—drawn 
off. ‘The center of gravity would then be slightly raised in the figure, 
and the center of volume still more so. The ocean side of the solid 
Earth has obviously a higher specific gravity than the continental 
side. 
It is the general opinion among geologists that the continental 
forms have always existed—that they are indestructible. How, then, 
could they have originated ? We know something of the permanent 
surface features of three bodies in the universe besides the Earth; 
namely, the Moon, Mars, and Mercury. None of these shows us 
anything resembling the irregular terrestrial distribution of the 
high-and low-level plains, of our continents and oceans. 
If we examine more minutely the coasts of our great oceans, we 
shall find the Pacific bounded by a nearly continuous line of active 
or extinct. volcanoes, and this is true whether in North or South 
America, Asia, the East Indies, New Zealand, or Antarctica. The 
only possible break is the east coast of Australia, but even here there 
is a line of volcanic islands, lying a short distance off the coast, 
stretching from New Guinea more than half-way to New Zealand. 
The coasts of the Pacific are generally mountainous and abrupt, 
and composed of curves convex toward the ocean. 
The Atlantic coasts, on the other hand, are generally low, flat, 
and composed of curves as often concave as convex. As to vol- 
canoes, they are few and scattering. The only conspicuous exception 
to the general rule is the range of the Lesser Antilles, which both 
in form and volcanic nature reminds us of the Pacific coast of Asia. 
The Indian Ocean resembles the Atlantic, except where it approaches 
the vicinity of the Pacific, and there the characteristic volcanoes 
again appear. 
A curious feature of the Atlantic Ocean is that the two sides 
have in places a strong similarity. Figure 4 is drawn in globular 
projection, which is used so frequently for the hemispheres in ordinary 
atlases, except that in this instance the projection is carried over the 
Pole onto the other side. This projection gives very little distortion 
