The author is grateful to the National Endowment for the Humanities and the American Philosophical Society for supporting portions of the research on which this article is based.

¹ Ostwald's most explicit formulations of the purposes of the Bridge came in his two brief booklets, Die Brücke (Munich, 1913)Google Scholar, and Die Organisierung der Organisatoren durch die Brücke (Munich, 1914).Google Scholar

² Like the post-war Vienna Circle, the pre-war ‘unity of science’ efforts were centred in Germanic culture, with the major exception of the British philosopher of science Pearson, Karl. Many ‘unity of science’Google Scholar efforts arose from the revolt of the German materialistic school of the 1850s against the Hegelian-tinged ‘officiai philosophy’ of state-controlled German universities. The leading members of the school, Moleschott, Jacob (1822–1893)Google Scholar and Vogt, Karl (1817–1895)Google Scholar, portrayed scientific materialism as a creed of social and political reform in Germany. Similar views were espoused by the two major popularizers of Darwinism in Germany, Büchner, Ludwig (1824–1899)Google Scholar, the author of Force and matter, and Haeckel, Ernst (1834–1919)Google Scholar, whose Riddles of the universe become the best-selling popular scientific book of the nineteenth and early twentieth centuries. The positivist Jodl, Friedrich (1849–1914)Google Scholar, professor of philosophy at Prague and later at Vienna, hoped to unify science through an amalgam of ‘Darwinism and ethics’. Haeckel and Jodl were prominent members of the German Monistic Alliance, founded in 1906. Ostwald's involvement in the Alliance is referred to later in this article. For a review of international scientific enterprises and conferences during the forty years preceding the First World War, see Schröder, Brigitte, ‘Charactéristiques des relations scientifiques internationales, 1870–1914’. Journal of world history, x (1966), 161–77.Google Scholar The pre-war ‘unity of science’ movements furnish a marked contrast to the post-war Einheitswissenschaft of Otto Neurath and Rudolf Carnap, who sought a synthesis of mathematical logic and the methods of contemporary physics. See Morris, Charles W. (ed.), Otto Neurath and the unity of science movement (Jerusalem, 1966).Google Scholar

³ Ostwald, Wilhelm, Monism as the goal of civilization (Hamburg, 1913), p. 32.Google Scholar The concept is also discussed in Ostwald, , Die Organisation der Welt (Basel, 1910).Google Scholar

⁴ Ostwald, , Die Überwindung des wissenschaftlichen Materialismus. Vortrag, gehalten in der dritten allgemeinen Sitzung der Gesellschaft deutscher Naturforscher und Ärzte zu Lübeck am 20. September 1895 (Leipzig, 1895), p. 26.Google Scholar Ostwald's thoughts on Energism also appeared as Die Energie und ihre Wandlungen. Antrittsvorlesung gehalten am 23. November 1887 in der Aula der Üniversitat Leipzig (Leipzig, 1888)Google Scholar, and as ‘Studien zur Energetik’, Zeitschrift für physikalische Chemie, ix (1892), 563–78, and x (1892), 363–8.Google Scholar

⁵ Ostwald, in a review of Wien, W., ‘Über den Begriff der Lokalisierung der Energie’, published in the Zeitschrift für physikalische Chemie, ix (1892), 771.Google Scholar

⁶ Ostwald, , ‘Der energetische Imperativ’, in Annalen der Naturphilosophie, x (1911), 113–17.Google Scholar See also ‘Der energetische Imperativ’, Monistische Sonntagspredigten (4 vols., Leipzig, 1911–1914), i. 97–104Google Scholar, and ‘Die wissenschaftlichen Grundlagen der Ethik’, ibid., iv. 389–404.

⁷ For a more complete explanation of ‘scientific efficiency’ and Energism, see my article, ‘A note on Wilhelm Ostwald's Energism’, Isis, Ixi (1970), 386–9.Google Scholar

⁸ Ostwald, , op. cit. (3), pp. 32–3.Google Scholar

⁹ Ostwald, , Denkschrift über die Grundung eines internationalen Instituts für Chemie (Leipzig, 1912), p. 30.Google Scholar

¹⁰ The foundation of the Gesellschaft für Elektrochemie occurred in the same year as the publication of Ostwald, 's Elektrochemie. Ihre Geschichte und Lehre (Leipzig, 1894).Google Scholar

¹¹ The Klassiker der exakten Wissenschaften, begun in 1889Google Scholar, eventually included more than 195 inexpensive popular editions of classic scientific works. The Annals, which appeared in 14 volumes beginning in 1901, carried the full title of Annalen der Naturphilosophie der Natur und Kulturphilosophie. Several volumes were later reprinted under the title Ein Jahrzehnt Naturphilosophie.

¹² Ostwald outlined his views on international auxiliary languages in three pamphlets: Die internationale Hilfssprache und das Esperanto: Vortrag, gehalten am 7. November 1906 in der Aula der Handelshochschule zu Berlin (Berlin, n.d.), Die Weltsprache (no place or date of publication given), and Sprache und Verkehr (Leipzig, 1911).Google Scholar The extent of Ostwald's commitment to the Esperanto project is indicated by a letter in which he wrote to one correspondent: ‘I have given up my professorship and all my official duties and am living as a free lance, spending the better part of my time and energy for the propagation of the idea of the international auxiliary languages’; see Ostwald to Charles Norton, 30 December 1906, in William James Papers, Houghton Library, Harvard University.

¹³ Ostwald to Mach, 24 February 1912, quoted in Thiele, J., ‘Naturphilosophie und Monisimu um 1900’, Philosophia naturalis, x (1967–1968), 305–6.Google Scholar One of Mach's correspondents, Joseph Petzoldt, wrote to Mach: ‘Ostwald shall yet regret his refusal to sign our appeal for the founding of a Society for Positive Philosophy’; see ibid., p. 306. On the membership of the Bridge, see Ostwald, , Lebenslinien. Eine Selbstbiographie (3 vols., Berlin, 1926–1927), iii (1927), 299f.Google Scholar

¹⁴ Herneck, Friedrich, Wissenschaft contra Gottesglauben. Aus den atheistischen Schriften des grossen Chemikers (Jena, 1960).Google Scholar

¹⁵ Ostwald, attempted to explain his synthesis of Energism and Monism in Energetische Grundlagen der Kulturwissenschaft (Leipzig, 1909).Google Scholar See also my article, ‘Ernst Haeckel's monistic religion’, Journal of the history of ideas, xxxii (1971), 265–80.Google Scholar

¹⁶ Ostwald was frequently viewed, outside Germany, as one of the German scientific community's most effective propagandiste for the country's war effort; see Paul, Harry L., The sorcerer's apprentice. The French scientist's image of German science, 1840–1919 (Gainesville, Fia., 1972) P. 30n.Google Scholar Within Germany, and particularly within the monistic movement, he was often regarded as a proponent of pacifism and arrtimilitarist ideas. Before the war, Ostwald termed pacifism a ‘scientific duty’ and urged that France should take the initial steps toward reconciliation with Germany; see Ostwald, W. (ed.), Frankreich als Friedensbringer (Berlin, 1911).Google Scholar During the war, he distinguished between pacifiste who opposed war per se and those who opposed war as a detriment to ‘cultural advances’. He identified himself with the latter, which he termed ‘cosmopolitan pacifism’; he wrote that ‘cosmopolitan pacifists’ would attempt to alleviate suffering and to defend Germany against ‘lies’. He described his journey to Sweden in the early months of the war as the mission of a Kriegsfreiwilliger (war-time volunteer) to deny German ‘guilt’ in the events that led to the war; see Ostwald, , Lebenslinien, op. cit. (13), iii. 344–5.Google Scholar In speeches to German audiences during the autumn of 1914, Ostwald denied that the enemy powers had the destruction of Prussian militarism as their main goal. He added: ‘We are not at war with scholars’. He pronounced himself a ‘convinced pacifist’ and said that he believed that a peaceful settlement was ‘still possible’; see Das monistische Jahrhundert, viii (2 11 1914), 620–4.Google Scholar By contrast, his fellow-Monist Haeckel replied that he favoured the invasion of the ‘British pirate states’, the annexation of Eastern Belgium and the ‘Baltic provinces’, and the forcible German assumption of the ‘greater part of the British colonial empire’; see Das monistische Jahrhundert, viii (16 11 1914), 657f.Google Scholar See also Kellermann, Hermann (ed.), Der Krieg der Geister. Eine Auslese deutschtr und ausländischer Stimme zur Weltkriege (Weimar, 1915), pp. 28–9, 110–11, 244–6, 251–3.Google Scholar During 1915 Ostwald came under increasing criticism from a small group of fellow-Monists for publishing ‘antimilitarist and pacifist’ articles in the journal of the movement. Partly because of such criticism, he resigned as president of the Alliance late in 1915.