CONTINENT. Though no mathematical distinction has ever been drawn between a C. and an island, the usage of language has generally recognized five great masses or divisions of land as continents—Europe, Asia, Africa, America, and Australia. Europe, Asia, and Africa form properly one great C., the only one known to the ancients; the second was discovered by Columbus; and the third made its appearance at the antipodes of Europe in the beginning of the 17th century. The existence of an antarctic C. has not yet been satisfactorily established. The apparent irregularity in the shape of the conti nents disappears on nearer examination, and certain uniformities become apparent, the causes of which have long been subjects of speculation. Bacon remarked, that the con tinents were pointed towards the south polar sea, and presented broad conformations toward the north. J. R. Forster followed up this remark by the generalization, that these southern points are the ends of mountain-ranges, which are continued northwards; and that at the e. side of these promontories there are always larger or smaller archipel agos of islands, while the w. side of the continents is indented with large bays.
Not only have attempts been made to reduce the horizontal outlines of the continents to rule, but their vertical dimensions have been Examined with the same view. Obser vation had been confined to ascertaining the heights of individual summits, Alex ander von Humboldt enriched physical geography with a new numerical element, by endeavoring to determine the mean height of continents—i.e., the elevation of the cen ter of gravity of their mass. Ile estimated the mean height of Europe at 103 toises (a toise is about 6 ft. 6 in.), of North America at 117, of South America at 177, and of Asia at 180 toises. Laplace had calculated the mean height of all the continents at 1000 meters; Humboldt found this too great by two thirds, and gives the height of the center of gravity of all the continents, except Africa, above the sea-level at 307 meters, or 1007 feet.