W. W. Ford, _The Life and Work of Robert Koch_, Bulletin of the Johns Hopkins Hospital, Dec. 1911, vol. 22. C. A. Herter, _The Influence of Pasteur on Medical Science_, Bulletin of the Johns Hopkins Hospital, Dec. 1903, vol. 14. E. O. Jordan, _General Bacteriology_ (fourth edition, 1915). Charles C. W. Judd, _The Life and Work of Lister_, Bulletin of the Johns Hopkins Hospital, Oct. 1910, vol. 21. Stephen Paget, _Pasteur and After Pasteur_. W. T. Sedgwick, _Principles of Sanitary Science_. René Vallery-Radot, _Life of Pasteur_. CHAPTER XVII SCIENCE AND INVENTION--LANGLEY'S AEROPLANE In his laudation of the nineteenth century Alfred Russel Wallace ventured to enumerate the chief inventions of that period: (1) Railways; (2) steam navigation; (3) electric telegraphs; (4) the telephone; (5) friction matches; (6) gas-lighting; (7) electric-lighting; (8) photography; (9) the phonograph; (10) electric transmission of power; (11) Röntgen rays; (12) spectrum analysis; (13) anæsthetics; (14) antiseptic surgery. All preceding centuries--less glorious than the nineteenth--can claim but seven or eight capital inventions: (1) Alphabetic writing; (2) Arabic numerals; (3) the mariner's compass; (4) printing; (5) the telescope; (6) the barometer and thermometer; (7) the steam engine. Similarly, to the nineteenth century thirteen important theoretical discoveries are ascribed, to the eighteenth only two, and to the seventeenth five. Of course the very purpose of these lists--namely, to compare the achievements of one century with those of other centuries--inclines us to view each invention as an isolated phenomenon, disregarding its antecedents and its relation to contemporary inventions. Studied in its development, steam navigation is but an application of one kind of steam engine, and, moreover, must be viewed as a phase in the evolution of navigation since the earliest times. Like considerations would apply to railways, antiseptic surgery, or friction matches. The nineteenth-century inventor of the friction match was certainly no more ingenious (considering the means that chemistry had put at his disposal) than many of the savages who contributed by their intelligence to methods of producing, maintaining, and using fire. In fact, as we approach the consideration of prehistoric times it becomes difficult to distinguish inventions from the slow results of development--in metallurgy, tool-making, building, pottery, war-gear, weaving, cooking, the domestication of animals, the selection and cultivation of plants. Moreover, it is scarcely in the category of invention that the acquisition of alphabetic writing or the use of Arabic numerals properly belongs.