And then--who can imagine, who dare predict, the social and economic revolution that must follow? Our social and business life to-day differs more widely from that of our grandfathers than theirs differed from the life of the Egyptian and Babylonian of three thousand years ago; but this gap is as ditch to cañon compared with the gap that separates us from the life of that generation of our descendants which shall have learned the secret of making food-stuffs from inorganic matter in the laboratory and factory. It is a long road to travel, I repeat; but modern science travels swiftly and with many short-cuts, and it may reach this goal more quickly than any conservative dreamer of to-day would dare to predict. All speed to the ambitious voyager! APPENDIX REFERENCE LIST AND NOTES CHAPTER I MAN AND NATURE For a general discussion of primitive conditions of labor and prehistoric man's civilization, it will be of interest in connection with this chapter to consult volume I., chapter I., which deals with prehistoric science. The appendix notes on that chapter (vol. I., pp. 302, 303) refer to some books which may be consulted for fuller information along the same lines. CHAPTER II HOW WORK IS DONE (p. 31). For study of Archimedes, giving a detailed account of his discoveries, see vol. I., p. 196 _seq._ It will be of interest also to review, in connection with this chapter, the story of the growth of knowledge of mechanics in the time of Galileo, Descartes, and Newton as told in the chapters entitled "Galileo and the New Physics," vol. II. (p. 93 _seq._), and "The Success of Galileo in Physical Science," vol. II., p. 204 _seq._ CHAPTER III THE ANIMAL MACHINE For further insight into the activities of the animal machine, the reader may refer to various chapters on the progress of physiology and anatomy in earlier volumes. The following references will guide to the accounts of the successive advances from the earliest time: Vol. I., pp. 194, 195 describe briefly the earlier anatomical studies of the Alexandrian physicians, Herophilus and Erasistratus; and pp. 282, 283, outline the studies of the famous physician, Galen. Vol. II., "From Paracelsus to Harvey," in particular, p. 163 _seq._; and chapters IV. (p. 173 _seq._) and V. (p. 202 _seq._) dealing with the progress of anatomy and physiology in the eighteenth and nineteenth centuries respectively. The chapter on "Experimental Psychology" (p. 245 _seq._) may also be consulted. Vol. V., chapter V., dealing with the Marine Biological Laboratory at Naples (p. 113 _seq._) and chapter VI., "Ernst Haeckel and the New Zoology" (p. 144 _seq._) present other aspects of physiological problems. CHAPTER IV THE WORK OF AIR AND WATER On page 63 reference is made to the work of the old Greeks, Archimedes and Ctesibius. An account of Archimedes' discovery of the laws of buoyancy of solids and liquids will be found in vol. I., p. 208.