What is true of man's precursors in the animal scale is, of course, true in a wider and fuller sense of man himself at the very lowest stage of his development. Ages before the time which the limitations of our knowledge force us to speak of as the dawn of history, man had reached a high stage of development. As a social being, he had developed all the elements of a primitive civilization. If, for convenience of classification, we speak of his state as savage, or barbaric, we use terms which, after all, are relative, and which do not shut off our primitive ancestors from a tolerably close association with our own ideals. We know that, even in the Stone Age, man had learned how to domesticate animals and make them useful to him, and that he had also learned to cultivate the soil. Later on, doubtless by slow and painful stages, he attained those wonderful elements of knowledge that enabled him to smelt metals and to produce implements of bronze, and then of iron. Even in the Stone Age he was a mechanic of marvellous skill, as any one of to-day may satisfy himself by attempting to duplicate such an implement as a chipped arrow-head. And a barbarian who could fashion an axe or a knife of bronze had certainly gone far in his knowledge of scientific principles and their practical application. The practical application was, doubtless, the only thought that our primitive ancestor had in mind; quite probably the question as to principles that might be involved troubled him not at all. Yet, in spite of himself, he knew certain rudimentary principles of science, even though he did not formulate them. Let us inquire what some of these principles are. Such an inquiry will, as it were, clear the ground for our structure of science. It will show the plane of knowledge on which historical investigation begins. Incidentally, perhaps, it will reveal to us unsuspected affinities between ourselves and our remote ancestor. Without attempting anything like a full analysis, we may note in passing, not merely what primitive man knew, but what he did not know; that at least a vague notion may be gained of the field for scientific research that lay open for historic man to cultivate. It must be understood that the knowledge of primitive man, as we are about to outline it, is inferential. We cannot trace the development of these principles, much less can we say who discovered them. Some of them, as already suggested, are man's heritage from non-human ancestors. Others can only have been grasped by him after he had reached a relatively high stage of human development. But all the principles here listed must surely have been parts of our primitive ancestor's knowledge before those earliest days of Egyptian and Babylonian civilization, the records of which constitute our first introduction to the so-called historical period. Taken somewhat in the order of their probable discovery, the scientific ideas of primitive man may be roughly listed as follows: