Now if the substantial truth of what has been said be admitted, and I do not see how it can be successfully challenged, there arise one or two considerations of supreme importance. The first of these is that social history becomes more and more a history of social psychology. In social life we are watching the play of social mind expressed through the medium of the individual. The story of civilization is the record of the piling of idea on idea, and the transforming power of the whole on the environment. For tools, from the flint chip of primitive man, down to the finished instrument of the modern mechanic, are all so many products of human mentality. From the primitive dug-out to the Atlantic liner, from the stone spear-head to the modern rifle, in all the inventions of civilized life we are observing the application of mind to the conquest of time, space, and material conditions. Our art, our inventions, our institutions, are all so many illustrations of the power of mind in transforming the environment. A history of civilization, as distinguished from a mere record of biologic growth, is necessarily a history of the growing power of mind. It is the cumulative ideas of the past expressed in inventions and institutions that form the driving power behind the man of to-day. These ideas form the most valuable part of man's heritage, make him what he is, and contain the promise of all that he may become. So long as we confine ourselves to biologic evolution, the way in which qualities are transmitted is plain. There is no need to go beyond the organism itself. But this heritage of ideas, peculiarly human as it is, requires a "carrier" of an equally unique kind. It is at this point that the significance of what we have called the "social medium" emerges. The full significance of this was first seen by G. H. Lewes.[1] Writing so far back as 1879 he said:--