a space of sea so wide that the farther shore is invisible, and yet imagine the farther shore also.  You will see America across the Atlantic and Japan across the Pacific; but you cannot see, in one single effort of the imagination, an Atlantic of empty blue water stretching to an empty horizon, another beyond that equally vast and empty, another beyond that, and so on until you have spanned the thousand horizons that lie between England and America.  The mind, that is to say, works in steps and spans corresponding to the spans of physical sight; it cannot clear itself enough from the body, or rise high enough beyond experience, to comprehend spaces so much vaster than anything ever seen by the eye of man.  So also with the stretching of the horizon which bounded human knowledge of the earth.  It moved step by step; if one of Prince Henry’s captains, creeping down the west coast of Africa, discovered a cape a hundred miles south of the known world, the most he could probably do was to imagine that there might lie, still another hundred miles farther south, another cape; to sail for it in faith and hope, to find it, and to imagine another possibility yet another hundred miles away.  So far as experience went back, faith could look forward.  It is thus with the common run of mankind; yesterday’s march is the measure of to-morrow’s; as much as they have done once, they may do again; they fear it will be not much more; they hope it may be not much less.

The history of the exploration of the world up to the day when Columbus set sail from Palos is just such a history of steps.  The Phoenicians coasting from harbour to harbour through the Mediterranean; the Romans marching from camp to camp, from country to country; the Jutes venturing in their frail craft into the stormy northern seas, making voyages a little longer and more daring every time, until they reached England; the captains of Prince Henry of Portugal feeling their way from voyage to voyage down the coast of Africa—­there are no bold flights into the incredible here, but patient and business-like progress from one stepping-stone to another.  Dangers and hardships there were, and brave followings of the faint will-o’-the-wisp of faith in what lay beyond; but there were no great launchings into space.  They but followed a line that was the continuance or projection of the line they had hitherto followed; what they did was brave and glorious, but it was reasonable.  What Columbus did, on the contrary, was, as we shall see later, against all reason and knowledge.  It was a leap in the dark towards some star invisible to all but him; for he who sets forth across the desert sand or sea must have a brighter sun to guide him than that which sets and rises on the day of the small man.