That day the lad changed his teachers.

Of the session more than two months yet remained. Every few days he might have been seen at the store, examining books, drawing money reluctantly from his pocket, hurrying away with another volume. Sometimes he would deliver to the clerk the title of a work written on a slip of paper: an unheard-of book; to be ordered—perhaps from the Old World. For one great book inevitably leads to another. They have their parentage, kinship, generations. They are watch-towers in sight of each other on the same human highway. They are strands in a single cable belting the globe. Link by link David's investigating hands were slipping eagerly along a mighty chain of truths, forged separately by the giants of his time and now welded together in the glowing thought of the world.

Not all of these were scientific works. Some were works which followed in the wake of the new science, with rapid applications of its methods and results to other subjects, scarce conterminous or not even germane. For in the light of the great central idea of Evolution, all departments of human knowledge had to be reviewed, reconsidered, reconceived, rearranged, rewritten. Every foremost scholar of the world, kindling his own personal lamp at that central sunlike radiance, retired straightway into his laboratory of whatsoever kind and found it truly illuminated for the first time. His lamp seemed to be of two flames enwrapped as one; a baleful and a benign. Whenever it shone upon anything that was true, it made this stand out the more clear, valuable, resplendent. But wherever it uncovered the false, it darted thereat a swift tongue of flame, consuming without mercy the ancient rubbish of the mind. Vast purification of the world by the fire of truth! There have been such purifications before; but never perhaps in the history of the race was so much burned out of the intellectual path of man as during the latter half of the nineteenth century.

There is a sort of land which receives in autumn, year by year, the deposit of its own dead leaves and weeds and grasses without either the winds and waters to clear these away or the soil to reabsorb and reconvert them into the materials of reproduction. Thus year by year the land tends farther toward sterility by the very accumulation of what was once its life. But send a forest fire across those smothering strata of vegetable decay; give once more a chance for every root below to meet the sun above; for every seed above to reach the ground below; soon again the barren will be the fertile, the desert blossom as the rose. It is so with the human mind. It is ever putting forth a thousand things which are the expression of its life for a brief season. These myriads of things mature, ripen, bear their fruit, fall back dead upon the soil of the mind itself. That mind may be the mind of an individual; it may be the mind of a century, a race, a civilization. To the individual, then, to a race, a civilization, a century, arrives the hour when it must either consume its own dead or surrender its own life. These hours are the moral, the intellectual revolutions of history.

The new science must not only clear the stagnant ground for the growth of new ideas, it must go deeper. Not enough that rubbish should be burned: old structures of knowledge and faith, dangerous, tottering, unfit to be inhabited longer, must be shaken to their foundations. It brought on therefore a period of intellectual upheaval and of drift, such as was once passed through by the planet itself. What had long stood locked and immovable began to move; what had been high sank out of sight; what had been low was lifted. The mental hearing, listening as an ear placed amid still mountains, could gather into itself from afar the slip and fall of avalanches. Whole systems of belief which had chilled the soul for centuries, dropped off like icebergs into the warming sea and drifted away, melting into nothingness.

The minds of many men, witnessing this double ruin by flame and earthquake, are at such times filled with consternation: to them it seems that nothing will survive, that beyond these cataclysms there will never again be stability and peace—a new and better age, safer footing, wider horizons, clearer skies.

It was so now. The literature of the New Science was followed by a literature of new Doubt and Despair. But both of these were followed by yet another literature which rejected alike the New Science and the New Doubt, and stood by all that was included under the old beliefs. The voices of these three literatures filled the world: they were the characteristic notes of that half-century, heard sounding together: the Old Faith, the New Science, the New Doubt. And they met at a single point; they met at man's place in Nature, at the idea of God, and in that system of thought and creed which is Christianity.

It was at this sublime meeting-place of the Great Three that this untrained and simple lad soon arrived—searching for the truth. Here he began to listen to them, one after another: reading a little in science (he was not prepared for that), a little in the old faith, but most in the new doubt. For this he was ready; toward this he had been driven.

Its earliest effects were soon exhibited in him as a student. He performed all required work, slighted no class, shirked no rule, transgressed no restriction. But he asked no questions of any man now, no longer roved distractedly among the sects, took no share in the discussions rife in his own church. There were changes more significant: he ceased to attend the Bible students' prayer-meeting at the college or the prayer-meeting of the congregation in the town; he would not say grace at those evening suppers of the Disciples; he declined the Lord's Supper; his voice was not heard in the choir. He was, singularly enough, in regular attendance at morning and night services of the church; but he entered timidly, apologetically, sat as near as possible to the door, and slipped out a little before the people were dismissed: his eyes had been fixed respectfully on his pastor throughout the sermon, but his thoughts were in other temples.