INTRODUCTION Natural Standards The aim of the two studies in this volume is to explore the technical and cultural dimen- sions of the engagement of two late 19th century physicists in measurement projects. Hen- ry Augustus Rowland and Albert Abraham Michelson were educated in physics and engineering in the United States, developed their physics in dialogue with European mas- ters, visited the continent, and as experimentalists and laboratory leaders set out to leave their professorial mark on a growing discipline in their homeland. Both physicists exem- plify the linkage between engineering and physics that has been regarded as typical of the United States in the late nineteenth century, but both stressed the importance of purity. Their personal engagement with industry shows that they saw a strong and mutual inter- play between scientific work and industry; but accorded science a very particular role in this relationship. Rowland’s experimental programs clearly demonstrate his certainty that advanced industry offered science the most appropriate machines and technologies for modern experimental work, while attention to detail and control of the environment would enable scientists to use these means with unprecedented accuracy. Their work bringing scientific accuracy to the most basic industrial technology, the screw, is emblem- atic of both Rowland and Michelson’s engagement with industrial concerns. It is charac- teristic to downplay the importance of their measurement projects, but as these papers will demonstrate, Rowland and Michelson understood the search for standards to be produc- tive of new science in a variety of ways. For example, as strongly bent on a universal sys- tem of units as he was, Rowland showed that the regime of absolute standards employed in his experiments entailed new and unexpected effects. Similarly, Michelson’s search for a suitable natural standard disclosed a fine structure to the spectra of elements that had not hitherto been visible with the finest diffraction gratings. The exploration of their encoun- ter with the different cultures of physics in their day, their engagement with instruments and their work with measurement will provide a new perspective on the changing culture of precision. The papers were written on the occasion of a workshop “Instruments, Travel and Science: Itineraries of Precision from the Seventeenth to the Twentieth Century” organised by Marie-Noëlle Bourguet, Christian Licoppe and H. Otto Sibum. But the topic of natural standards has been further investigated in the Independent Research Group “Experimental History of Science” at the Max Planck Institute for the History of Science. NATURAL STANDARDS Exploring the Margins of Precision H. Otto Sibum EXPLORING THE MARGINS OF PRECISION This paper will take you on a journey through Europe during the years 1875 and 1876. Our traveller is the American civil engineer and instructor of physics at Rensselaer Poly- technic, Henry A. Rowland. He was sent (and accompanied for part of the journey) by the President of Johns Hopkins University, Daniel Coit Gilman, with the aim of studying the material culture of science in Europe. In particular he was to survey workmanship in lab- oratory physics, the quality of instrument making and the most important research topics pursued by European physicists. Equipped with substantial funds and looking forward to becoming the founding director of the new physics laboratory at Johns Hopkins Univer- sity in Baltimore, the twenty seven-year old physicist expected to do his most interesting and challenging fieldwork. Historians of science have paid little attention to this European trip, let alone to integrate Rowland’s experiences as a traveller with an understanding of his early laboratory physics at Johns Hopkins.1 Instead historians of physics customarily begin their accounts of Rowland’s career as a physicist with his famous optical investigations, the production and distribution of dif- fraction gratings, which represent the height of precision spectroscopy.2 When it is no- ticed at all, Rowland’s first major research “On the Mechanical Equivalent of Heat” (a 124 page text which appeared in the Proceedings of the American Academy of Arts and Science in 1880), is seen simply as an attempt to replicate a thirty-year old experiment to achieve an exact value for the mechanical equivalent of heat in absolute measures.3 By reconstituting his European experiences in great detail we will provide a hitherto neglect- ed perspective on this experiment, and simultanously give new insights about an impor- tant moment of change in the development of what has been called the culture of precision in the 19th century. 1. For this article I am making use in particular of Rowland’s “European Trip “diary, held at the Johns Hopkins University, The Milton S. Eisenhower Library, Special Collections, Rowland papers, Ms 6, Box 22 (archive material hereafter cited as JHU, Ms..., Rowland papers) and the relevant private and official correspondence by him held in JHU. The few accounts which refer to Rowland’s travel describe it either as a masterpiece of self-education, Samuel Rezneck, “The Education of an American Scientist: H.A. Rowland, 1848-1901”, American Journal of Physics, vol. 28, no. 1-9 (1960): 155-162 or convinc- ingly show relations between his travel and his later electro-magnetic research see John David Miller, “Rowland and the Nature of Electric Currents”, ISIS, vol. 63, no. 216 (1972): 5-27. 2. See for example George K. Sweetnam, “The Command of Light: Rowland’s School of Physics and the Spectrum,” (Unpublished Ph.D. dissertation at Princeton Univ., 1996). Idem, “Precision Implemented: Henry Rowland, the Concave Diffraction Grating, and the Analysis of Light,” in M. Norton Wise (ed.), The Values of Precision,(Princeton: Princeton University Press, 1995), pp. 283-310; Klaus Hentschel, “The Discovery of the Redshift of Solar Fraunhofer lines by Rowland and Jewell in Baltimore around 1890”, Historical Studies in the Physical Sciences (HSPS), vol. 23, no. 2 (1993): 219-277. 3. Henry A. Rowland, “On the Mechanical Equivalent of Heat, with Subsidary Researches on the Variation of the Mercurial from the Air Thermometer, and on the Variation of the Specific Heat of Water”, Pro- ceedings of the American Academy of Arts and Sciences, vol. XV(1880): 75-200, reprinted in The Phys- ical Papers of Henry Augustus Rowland, (Baltimore, Johns Hopkins University, 1902), pp. 343-468; Idem, “Appendix to Paper on the Mechanical Equivalent of Heat, Containing the Comparison with Dr. Joule’s Thermometer,” Proceedings of the American Academy of Arts and Sciences, vol. XVI (1881): 38-45. The Physical Papers of Henry Augustus Rowland, pp. 469-480. 3 H. OTTO SIBUM During the second half of the century precision measurement became an icon for the exact sciences, but it was clear to many that their striving for precision using ever more sensitive devices pushed the work of physics to its limits. In private correspondence with Rowland the German doyen of precision measurement Friedrich Kohlrausch brought out an important problematic with his discussion of the standards of accuracy that an envis- aged “international laboratory” would force on physicists’ experimental work. He con- ceded that “if an international laboratory wants to bestow unity upon science and technology this laboratory has to work much more precise than physi- cists have currently done... To bring a bunch of experienced physicists for this purpose permanently together seems impossible. Every one of us certainly knows that he would work best at home.”4 The tension between the local and global expressed in this remark points to a pressing issue of the time: the embodied character of experimental knowledge. Experimentalists’ insistence on working best at home or maintaining physical contact with objects and in- struments in producing new effects and experimental knowledge ran counter the modern view of science, which implied that true knowledge could only be achieved if it was in- dependent of the competencies of individual scientists or the peculiarities of a specific place. This paper will take a close look at a very delimited period of time in which preci- sion measurement became an ultimate technique to discriminate between what counted as local and what as scientific knowledge.5 When he met British scientists, Rowland experienced at first hand the work required to establish a “coherent system of units” with its absolute measures, as it was being 4. “Ich meine das die Verbürgung auf höchstens 1/1000 Fehler vorausgesetzt werden muß, wenn ein inter- nationales Laboratorium die Einheit von Wissenschaft und Technik octroyren will. Zu diesem Zwecke aber müßte dieses Laboratorium wesentlich genauer arbeiten, als die Physiker bis jetzt gethan haben... Eine Anzahl erfahrener Physiker aber zu diesem Zwecke dauernd zu vereinigen, wird unmöglich sein. Es weiß ja auch jeder von uns, daß er zu Hause am besten arbeitet”, Kohlrausch to Rowland 28 April, 1882, JHU, Rowland papers, MS 6. 5. Historians of science have investigated the 19th century culture of precision in a number of ways. See for example Theodore Porter, Trust in Numbers: the pursuit of objectivity in science and public life, (Princeton: Princeton University Press, 1995); M. Norton Wise (ed.), The Values of Precision, 1995, op. cit.; Kathryn M. Olesko, Physics as a Calling: Discipline and Practice in the Königsberger Seminar for Physics (Ithaca, N.J.: Cornell University Press, 1991), Lorraine Daston and Peter Galison, “The Image of Objectivity”, Representations, vol. 40 (1992): 81-128. Lorraine Daston, “The Moral Economy of Sci- ence”, Osiris, vol. 10 (1995): pp. 3-24. Simon Schaffer, “Accurate Measurement is an English Science”, in: M. Norton Wise (ed.), The Values of Precision, op.cit. (note 2), pp. 135-172. This paper investigates the meaning of experiment within this context. 4 EXPLORING THE MARGINS OF PRECISION promoted by the British Association for the Advancement of Science.6 But he soon rec- ognised that the aims of this programme were far from being fully realised.