This retrospective logic may explain the presence and perennial charm of those panoramic pages in our encyclopaedias purporting to show forth the gradual perfecting of great instrumentalities upon which our modern life depends. We survey the "evolution" of printing, for example, from the wooden blocks of the Chinese or of Laurens Coster down to the Hoe press, the stereotype plate, and the linotype machine. Or we see the forms of written record from pictured papyrus, cuneiform brick, and manuscript scroll down to the printed book and the typewritten page; the means of carriage by land from the ox-cart of the patriarchs to the stage-coach, the Cannonball Limited, the motor-truck, and the twelve-cylinder touring-car. And as one contemplates these cheerfully colored exhibits there is in each case an almost irresistible suggestion of a constant and compelling need of "universal man" seeking in more and more marvellously ingenious ways an adequate expression and satisfaction. This need seems never to have lapsed or changed its nature. All along both driving power and direction, it has been the one fixed factor in a long process in which all else has been fluctuating, contingent, and imperfect--all else except the nature of the materials and the principles of mechanics, which, too, are seen in the end to have been mutely conspiring toward the result. Essential human nature, it seems clear, does not and happily cannot change. Spiritual progress, in this ultimate optimism, means simply clearer vision, completer knowledge, and a less petulant and self-assertive habit of insistence upon the details of particular purposes as individual "impulse" and "idiosyncrasy" define them. We fortunate beings of today have available, in the various departments of our life, certain instrumentalities, and to these our interests attach. These interests of ours in their proportional strength (so the argument runs) express our native and generic constitution in so far as this constitution has been able as yet to achieve outward expression and embodiment. And accordingly, in interpreting the long history of technological evolution, we take what we conceive ourselves now to be as normative and essential. We project back into the lives of primitive man, of our own racial ancestors, or of our grandfathers, the habits and requirements which we acknowledge in ourselves today and we conceive the men of the past to have been driven forward on the ways of progress by the identical discontent that would presumably beset ourselves if we were to be suddenly carried back to their scale and manner of existence.