How was the world discovered? That is to say, how did a certain set of men who lived round the Mediterranean Sea, and had acquired the art of recording what each generation had learned, become successively aware of the other parts of the globe? Every part of the earth, so far as we know, has been inhabited by man during the five or six thousand years in which Europeans have been storing up their knowledge, and all that time the inhabitants of each part, of course, were acquainted with that particular part: the Kamtschatkans knew Kamtschatka, the Greenlanders, Greenland; the various tribes of North American Indians knew, at any rate, that part of America over which they wandered, long before Columbus, as we say, "discovered" it.