The conjunction of environment with a certain organized complexity of grey matter was hardly ever more important to the world than that of Mohammed. The powerful frame, abundant black hair, wonderful dark eyes, and great imposing head may well have attracted the rich widow who “made his fortune” by marrying him, and they stood him in good stead in his later adventurous career. But nothing short of a unique arrangement of his reflex-arcs, chiefly in the association-areas of his brain, could have opened up to him the world of Asia and Europe. Columbus. Who can doubt that it was ultimately to the inherited structure of the convolutions of his brain that Columbus owed his great achievement in opening up a New World; or that to the reactionary and intense “character” of Philip’s brain the persecutions in the Netherlands were due; and on the other hand that to the brain of William of Orange with its liberal and enlightened “character” the Seven Provinces that resisted Philip owed their freedom; the results in the two cases being the decay of Spain from that time forward, and the final success in the struggle for religious liberty. In such a view of historical facts it is not necessary either to follow Carlyle in his extreme claims for the influence of great men and heroes, nor to look upon the hero as an epiphenomenon. It is certain that eventually some other great man would have arisen to do what the great Genoese did, if he had not done it, and as it is claimed that Amerigo di Vespucci did, and it is certain that Philip was only the last of the Hapsburg sovereigns who determined the fall of Spain, and that Huss, Jerome, Wycliffe and Luther in their days initiated the struggle for religious liberty which Holland brought to success. But the facts referred to can hardly be disputed, and the men and their “characters” did certainly determine permanent changes in the world. Napoleon. Among individual men of modern times none strikes the imagination as does Napoleon. Without ignoring the tremendous outburst of the soul of down-trodden France at the Revolution, it cannot be denied that the “character” or grey matter of brain of the man of whom it is said “nothing where he had passed was as it had been before,” was the dominant and natural fact that changed the face of Europe. What physical quality had Napoleon, except those of his grey cells, which could have led him to such results on the environment into which he was cast? Migrations.