The ocean has always performed one function in the evolution of history; it has provided the outlet for the exercise of redundant national powers.  The abundance of opportunity which it presents to these disengaged energies depends upon the size, location and other geographic conditions of the bordering lands.  These opportunities are limited in an enclosed basin, larger in the oceans, and largest in the northern halves of the oceans, owing to the widening of all land-masses towards the north and the consequent contraction of the oceans and seas in the same latitudes.

[Sidenote:  Contrasted historical roles of northern and southern hemispheres.]

A result of this grouping is the abundance of land in the northern hemisphere, and the vast predominance of water in the southern, by reason of which these two hemispheres have each assumed a distinct role in history.  The northern hemisphere offers the largest advantages for the habitation of man, and significantly enough, contains a population five times that of the southern hemisphere.  The latter, on the other hand, with its vast, unbroken water areas, has been the great oceanic highway for circum-mundane exploration and trade.  This great water girdle of the South Seas had to be discovered before the spherical form of the earth could be proven.  In the wide territory of the northern hemisphere civilization has experienced an uninterrupted development, first in the Old World, because this offered in its large area north of the equator the fundamental conditions for rapid evolution; then it was transplanted with greatest success to North America.  The northern hemisphere contains, therefore, “the zone of greatest historical density,” from which the track of the South Seas is inconveniently remote.  Hence we find in recent decades a reversion to the old east-west path along the southern rim of Eurasia, now perfected by the Suez Canal, and to be extended in the near future around the world by the union of the Pacific with the Caribbean Sea at Panama; so that finally the northern hemisphere will have its own circum-mundane waterway, along the line of greatest intercontinental intercourse.

[Sidenote:  Size of the oceans]

The size of the ocean as a whole is so enormous, and yet its various subdivisions are so uniform in their physical aspect, that their differences of size produce less conspicuous historical effects than their diversity of area would lead one to expect.  A voyage across the 177,000 square miles (453,500 square kilometers) of the Black Sea does not differ materially from one across the 979,000 square miles (2,509,500 square kilometers) of the Mediterranean; or a voyage across the 213,000 square miles (547,600 square kilometers) of the North Sea, from one across the three-hundredfold larger area of the Pacific.  The ocean does not, like the land, wear upon its surface the evidences and effects of its size; it wraps itself in the same garment of blue waves or sullen swell, wherever it