The leading interest of arctic exploration thus far, in connection with our present study, has been seen to be concerned with the opening of sea routes, by north-west and north-east, from Europe to Asia. The story of antarctic discovery, on the other hand, brings into prominence a problem of far different character which we have already had occasion to notice incidentally. It might be labelled as the problem of the Fifth Continent, though its origin dates from a period long before the discovery of the fourth. We have seen how the conception of a spherical earth was supported on grounds of speculative philosophy by the Pythagoreans, and proven by the observations of Aristotle. We have met with the Stoic conception of the four land-masses, one in each of the “four quarters” of the globe, of which but one, the _œcumene_, was known. Here, then, was the material already for an antarctic problem. There can be no doubt that its solution was regarded in ancient times as beyond the limit of human endeavour, because the passage of the torrid zone was held impossible in spite of those rumours of far southerly voyages, to which we have referred, and which might otherwise have pointed the way to further discovery. We pass over the period when the antipodean theory was maintained only by the freest of Christian thinkers, and resume the antarctic story at the point where Bartolomeu Diaz demonstrated by experience that the torrid climatic belt is not impassable, and entered a temperate belt to the south of it. After this, the discovery of Brazil, the frequent enforced voyages south of the Horn by mariners driven thither by storms, and the exploration of the Pacific, are all intimately associated with the antarctic problem. Spanish and Portuguese voyagers at the beginning of the sixteenth century revealed Brazil as continental land; a Portuguese expedition in 1514 reported the southern extremity of South America to be in 40° S., and asserted that the coast of a southern continent was observed beyond this. Ferdinand Magellan, again, passing in 1521 through the straits which bear his name, between the South American mainland and Tierra del Fuego, proved nothing as to the continental or insular character of the latter; but the general tendency of geographical theory favoured the idea of a continent. It took various shapes. We find its coastline roughly coincident with the Antarctic Circle according to Leonardo da Vinci’s globe constructed in 1515; this was at least a better estimate of its extent than that of Orontius of 1531, wherein the west of Terra Australis (“lately discovered but not yet fully known,” as it is ingenuously labelled) approaches close to the southern American promontory about 55° S., runs thence eastward between 50° and 60° S. to the south of Africa, extends northward to the latitude of southern Madagascar in the Indian Ocean, where the “region of Brazil” is found, and to the south-east of