1 For a discussion of the relationship between theory and experiment in gas discharge research see Erwin N. Hiebert, ‘Electric discharge in rarefied gases: the domination of experiment. Faraday. Plücker. Hittorf’, in Anne J. Knox and Daniel M. Siegel (eds.), No Truth Except in the Details, Dordrecht: Kluwer, 1995, pp. 95–134; Darrigol, Olivier, Electrodynamics from Ampère to Einstein, Oxford: Oxford University Press, 2002Google Scholar, for a dense and comprehensive discussion of nineteenth-century researches in gas discharge (and electrolysis); for a general introduction with a focus on late nineteenth-century developments see Per F. Dahl, Flash of the Cathode Rays: A History of J.J. Thomson's Electron, Bristol: IOP Publishing, 1997; Jed Z. Buchwald and Andrew Warwick (eds.), Histories of the Electron: The Birth of Microphysics, Cambridge, MA: MIT Press, 2001.

2 Grove, William R., ‘On the electrical discharge and its stratified appearance in rarefied media’ (1859), The Royal Institution Library of Science, Physical Sciences (1970) 1, p. 280Google Scholar.

3 One of these devices (purchased in 1863) can still be seen in Haarlem's Teyler Museum; for an image and description of the device and a short note on the two inventors see Turner, Gerard L'E., The Practice of Science in the Nineteenth Century: Teaching and Research Apparatus in the Teyler Museum, Haarlem: The Teyler Museum, 1996, p. 296Google Scholar.

4 Théodore Achille Louis du Moncel, Notice sur l'appareil d'induction électrique de Ruhmkorff, Paris: Hachette, 1855. In the preface of the German edition (Bromeis, C. and Bockelmann, J.F., Ruhmkorff's Inductions-Apparat und die damit anzustellenden Versuche. Nach dem französischen Original des Herrn Th. du Moncel mit dessen Autorisierung bearbeitet, Frankfurt am Main: Sauerländer, 1857Google Scholar) the editors report that during their stay in Paris, Ruhmkorff called their attention to the French original.

5 In a letter to Justus von Liebig from 2 February 1858 (Bayerische Staatsbibliothek, München, Liebigiana II B, Geißler, H.) Geissler reported a shipment of fifty tubes to Ruhmkorff. On Geissler, see Eichhorn, Karl, ‘Heinrich Geißler (1814–1879). Leben und Werk des Thüringer Glasinstrumentenbauers und Pioniers der Vakuumtechnik’, in Jahrbuch des Hennebergisch-Fränkischen Geschichtsvereins (1995) 10, pp. 207–233Google Scholar. In the Encyclopaedia Britannica, Geissler was later described as a ‘distinguished practical physicist’ who has been known not only for his ‘surpassing skill and ingenuity of conception in the fabrication of physical apparatus’, but also for his ‘comprehensive knowledge, acquired chiefly in his later life, of the natural sciences.’ Encyclopaedia Britannica, 9th edn, vol. 10, Akron, OH, 1900, p. 130.

6 La Rue, Warren De and Müller, Hugo W., ‘The electric discharge with the chloride of silver battery’, Nature (1879) 20, pp. 174–178, 174Google Scholar. A series of images taken during my own experiments with a discharge tube coming directly from the glass blower can be seen on the cover of my book: Müller, Falk, Gasentladungsforschung im 19. Jahrhundert, Berlin: GNT, 2004Google Scholar.

7 For example, Poggendorff, Johann C., ‘Untersuchung veranlaßt durch eine von Hrn. Holtz erfundene neue elektrische Röhre’, Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin (9 December 1867), Berlin: Königliche Akademie der Wissenschaften, 1868, p. 801Google Scholar. John Peter Gassiot doubted the scientific value of Geissler tubes he had obtained from Bence Jones and preferred tubes of his own construction (Gassiot, John Peter, ‘The Bakerian Lecture: on the stratifications and dark band in electrical discharge as observed in Torricellian vacua’, Philosophical Transactions of the Royal Society (1858) 148, pp. 1–16, 14CrossRefGoogle Scholar). Other researchers ordered their tubes at Geissler's even after vacuum tubes could easily be bought in their home country as well, for example the spectroscopist Piazzi Smyth who in 1877 tried to obtain original Geissler tubes via the instrument-maker Thomas Cooke & Sons in York because he preferred tubes made out of very thin glass. Hentschel, Klaus, Mapping the Spectrum: Techniques of Visual Representation in Research and Teaching, Oxford: Oxford University Press, 2002, p. 316 n. 253CrossRefGoogle Scholar.

8 During Arthur Schuster's studies in Heidelberg in 1871–1872 no glass-blower was available; it was the chemist Robert Bunsen who helped him to prepare a discharge tube (Schuster, Arthur, ‘Biographical byways’, Nature (1925) 115, pp. 126–127CrossRefGoogle Scholar, 126); at the Cavendish Laboratory he found similar conditions: ‘The facilities of the laboratory were not what students now expect. We had to charge our own batteries and learn a little glass blowing and ordinary workshop manipulations, as there were no instrument makers nearer than London.’ Schuster, Arthur, The Progress of Physics during 33 Years (1875–1908), Cambridge: Cambridge University Press, 1911, p. 28Google Scholar.

9 On the occasion of a demonstration of Geissler's pump at the Naturforscherversammlung at Gießen in 1864, Johann Christian Poggendorf observed ‘how easily unskilled hands could destroy the instrument.’ Poggendorf, Johann C., ‘Ueber eine neue Einrichtung der Quecksilber-Luftpumpe’, Annalen der Physik und Chemie (1865) 201, pp. 151–160, 153 and 158CrossRefGoogle Scholar.

10 Researchers such as Paalzow in Berlin and Poggendorf in Leipzig admitted their ignorance of the exact specifications of their Geissler tubes. Paalzow, Adolph, ‘Ueber die verschiedenen Arten der Entladung der Leydener Batterie, und über die Richtung des Haupt- und secundären Nebenstromes derselben’, Annalen der Physik und Chemie (1861) 188, pp. 567–587, 574; Poggendorf, op. cit. (8), p. 806 n. 1CrossRefGoogle Scholar.

11 For example, the Teyler Museum in Haarlem purchased ten Geissler tubes in 1859, fifteen more were purchased in 1862. Turner, op. cit. (3), pp. 294–295.

12 The physicist Otto Lehmann reported that in 1858 Ruhmkorff came to Karlsruhe to show his induction machine and the ‘marvellous discharge phenomena it produced’ on the occasion of a meeting of the Association of German Naturalists and Physicians. The local sovereign was so enthusiastic about the demonstration that he decided to purchase such a machine for the physics department of the Karlsruhe polytechnic school (Lehmann, Otto, Die elektrischen Lichterscheinungen oder Entladungen bezeichnet als Glimmen, Büschel, Funken und Lichtbogen in freier Luft und in Vacuumröhren, Halle: Knapp, 1898, p. 550Google Scholar); on the popularization of these effects see Iwan R. Morus, ‘“More the aspect of magic than anything natural”: the philosophy of demonstration’, in Aileen Fyfe and Bernhard Lightman (eds.), Science in the Marketplace, Chicago: University of Chicago Press, 2007, pp. 336–370, 356–357.

13 Friedrich Zöllner acted as intermediary; he stopped by at Geissler's workshop after a visit to Crookes's laboratory. Dörfel, Günter and Müller, Falk, ‘Crookes’ Radiometer und Geißlers Lichtmühle – Kooperation oder Konkurrenz?’, N.T.M/Journal of the History of Science, Technology and Medicine (2003) 11, pp. 171–190Google Scholar.

14 Meyer, W.H. Theodor, Beobachtungen über das geschichtete electrische Licht sowie über den merkwürdigen Einfluß des Magneten auf dasselbe nebst Anleitung zur experimentellen Darstellung der fraglichen Erscheinungen, Berlin: Springer, 1858, p. 14Google Scholar.

15 A wide range of Geissler tubes could still be found in a catalogue of Geissler's successor, the company Franz Müller, from 1904; Geissler tubes were sold as toys or for decorating shop windows. Images of luminous Geissler or Crookes tubes can be found on YouTube and elsewhere in the Internet.

16 Plücker to Michael Faraday, 3 July 1859, in L. Pearce Williams (ed.), The Selected Correspondence of Michael Faraday, 2 vols., Cambridge: Cambridge University Press, 1933, vol. 2, p. 925.

17 Plücker to his wife, 19 June 1862, Plücker Collection, Archive of the National Research Council of Canada, Ottawa (subsequently PCNRC).

18 Plücker to his wife, 14 October 1858, PCNRC.

19 Plücker was much more honoured in France and Britain than in Germany, where he was in a permanent conflict with his rival Jakob Steiner in Berlin. Eccarius, Wolfgang, ‘Der Gegensatz zwischen Julius Plücker und Jakob Steiner im Lichte ihrer Beziehungen zu August Leopold Crelle, Hintergründe eines wissenschaftlichen Meinungsstreites’, Annals of Science (1980) 37, pp. 189–213CrossRefGoogle Scholar; on Plücker's early career and his educational background see Fritz Krafft, ‘Dokumente zu Julius Plückers Marburger Promotion “in absentia”’, in Rudolf Seising, Menso Folkerts and Ulf Hashagen (eds.), Form, Zahl, Ordnung: Studien zur Wissenschafts- und Technikgeschichte, Stuttgart: Steiner, 2004, pp. 415–425; G. Warnecke, Julius Plücker (1801–1868) in der philosophischen Fakultät der Universität Halle (07.11.1833–25.09.1835) (Reports on Didactics and History of Mathematics 3/2004), Halle (Saale): Martin-Luther-University Halle-Wittenberg, Institute for Mathematics, 2004.

20 Clebsch, Alfred, ‘Zum Gedächtniss an Julius Plücker’, Abhandlungen der Königlichen Gesellschaft der Wissenschaften zu Göttingen (1871) 16, pp. 1–40, 5Google Scholar.

21 On the role of descriptive or projective geometry in the education of nineteenth-century German natural philosophers see M. Norton Wise, ‘What's a line?’, in Moritz Epple and Claus Zittel (eds.), Science as Cultural Practice, Berlin: Akademie, 2010, pp. 61–104; on projective geometry as a bridge between the inductive and the deductive sciences and on its ideological function in discussions on the use and value of mathematical education in Britain in the nineteenth century see Richards, Joan L., ‘Projective geometry and mathematical progress in mid-Victorian Britain’, Studies in History and Philosophy of Science (1986) 17, pp. 297–325CrossRefGoogle Scholar.

22 Herbert Mehrtens, ‘Mathematical models’, in Soraya de Chadarevian and Nick Hopwood (eds.), Models: The Third Dimension of Science, Stanford: Stanford University Press, 2004, pp. 276–306, 289; cf. Klein, Felix, Vorlesungen über die Entwicklung der Mathematik im 19. Jahrhundert, 2nd edn, Berlin: Springer, 1979, pp. 119–126CrossRefGoogle Scholar.

23 Rheinberger, Hans-Jörg, Towards a History of Epistemic Things: Synthesizing Proteins in the Test Tube, Stanford: Stanford University Press, 1997, pp. 24–37Google Scholar.

24 Julius Plücker, ‘Experimental-Untersuchungen über die Wirkung der Magnete auf gasförmige und tropfbare Flüssigkeiten’, Julius Plückers Gesammelte wissenschaftliche Abhandlungen (ed. Arthur Schoenflies and Friedrich Pockels), 2 vols, Leipzig: Teubner, 1895–1896, vol. 2, pp. 35–61.

25 Plücker, Julius, ‘On a new geometry of space’, in Julius Plückers Gesammelte wissenschaftliche Abhandlungen, op. cit. (24), vol. 1, pp. 462–545Google Scholar, 539 (originally published in the Proceedings of the Royal Society (1865) 13).

26 De la Rive's researches on gas discharge phenomena are summarized in de la Rive, Auguste, ‘On the propagation of electricity in highly rarefied elastic fluids, and in particular on the stratifications of the electric light in very rare media’, London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science (1867) 33, pp. 241–261CrossRefGoogle Scholar, 512–530, 512 (electrodynamic character of the positive light).

27 Plücker to Faraday, 27 December 1857, in Williams, op. cit. (16), p. 891.

28 Plücker, Julius, ‘Abstract of a series of papers and notes concerning the electrical discharge through rarefied gases and vapours’, Proceedings of the Royal Society (1858–1859) 10, p. 259Google Scholar.

29 Plücker, op. cit. (28), p. 258.

30 Iron filings provide ‘von der Vertheilung der magnetischen Kraft um die Pole irgend eines Magneten auch da noch ein anschauliches Bild, wo die mathematische Analyse nicht mehr ausreicht, und bieten überhaupt für diese eine Art Ersatz’. Plücker, Julius, ‘Mittheilung über eine neue physikalische Erscheinung’, Verhandlungen des naturhistorischen Vereins der preussischen Rheinlande und Westphalens (1858) 15, p. xxxGoogle Scholar.

31 On Faraday's gas discharge research and his discussion of the relationship between electricity and matter, see Williams, L. Pearce, Michael Faraday, New York: Basic Books, 1965; Hiebert, op. cit. (1), pp. 95–100Google Scholar; see ibid. for Plücker's varying attempts to explain the phenomena.

32 Plücker, Julius, ‘Ueber die Einwirkung des Magneten auf die elektrische Entladung’, Annalen der Physik und Chemie (1861) 189, pp. 249–280, 520CrossRefGoogle Scholar.

33 Morren, Auguste, ‘Ueber die elektrische Leitungsfähigkeit der Gase unter schwachen Drucken’, Annalen der Physik und Chemie (1867) 206, pp. 612–636, 629CrossRefGoogle Scholar.

34 The English engineer Cromwell Varley picked up Plücker's research and introduced a further contemporary medium that was praised for its ‘mathematical sharpness’; in addition, the photographic plate showed features of the discharge which were not visible to the naked eye: ‘The eye and the collodion-plate do not, however, tell the same tale.’ Varley, Cromwell F., ‘Some experiments on the discharge of electricity through rarefied media and the atmosphere’, Proceedings of the Royal Society of London (1871) 19, pp. 236–242, 238CrossRefGoogle Scholar; on Varley's gas discharge research see Noakes, Richard, ‘Cromwell Varley FRS, electrical discharge and Victorian spiritualism’, Notes and Records of the Royal Society of London (2007) 61, pp. 5–22CrossRefGoogle Scholar.

35 Plücker, Julius, ‘Fortgesetzte Beobachtungen über die elektrischen Entladungen durch gasverdünnte Räume’, Annalen der Physik und Chemie (1858) 180, pp. 113–128, 123CrossRefGoogle Scholar; cited from Plücker, Julius, ‘Observations on the electrical discharge through rarefied gases’, Philosophical Magazine (1858) 16, pp. 408–418, 415Google Scholar.

36 Plücker, ‘Fortgesetzte Beobachtungen’, op. cit. (35) p. 128; for a comparable use of electricity in chemistry see Grove, William R., ‘On the molecular impressions by light and electricity’, Proceedings of the Royal Institution of Great Britain (1854–1858) 2, pp. 458–464Google Scholar.

37 Plücker, Julius, ‘Ueber die Einwirkung des Magneten auf die elektrischen Entladungen in verdünnten Gasen’, Annalen der Physik und Chemie (1858) 179, pp. 88–106, 151–157CrossRefGoogle Scholar, 90; idem, ‘On the action of the magnet upon the electrical discharge in rarefied gases’, Philosophical Magazine (1858) 16, pp. 119–135Google Scholar, 120.

38 Plücker, ‘Fortgesetzte Beobachtungen’, op. cit. (35), p. 128; cited from Plücker, ‘Observations on the electrical discharge through rarefied gases’, Philosophical Magazine (1858) 16, pp. 408–418Google Scholar, 418.

39 Plücker to his wife, 12 and 15 April 1862, PCNRC.

40 Hittorf to Heinrich Kayser, 14 November 1899, Staatsbibliothek Preußischer Kulturbesitz, Berlin, Sammlung Darmstaedter (subsequently SPKSD), F1e 1869 (3); in Britain, Norman Lockyer collaborated with the chemist Edward Frankland, and Willliam Huggins with the chemist W.A. Miller, in their spectroscopic investigations. Simon Schaffer, ‘Where experiments end: tabletop trials in Victorian astronomy’, in Jed Z. Buchwald (ed.), Scientific Practice: Theories and Stories of Doing Science, Chicago: University of Chicago Press, 1995, pp. 257–299, 275–276, 288.

41 For a history of the seminar see Schubring, Gert, ‘The rise and decline of the Bonn natural science seminar’, Osiris (1989) 5, pp. 57–93CrossRefGoogle Scholar. A short discussion of the Bonn seminar and a comparison with a similar institution in Königsberg is given in Olesko, Kathryn M., Physics as a Calling: Discipline and Practice in the Königsberg Seminar for Physics, Ithaca: Cornell University Press, 1991, pp. 47–55Google Scholar; for a general discussion of the seminar culture in Germany see Jungnickel, Christa and McCormmach, Russell, Intellectual Mastery of Nature: Theoretical Physics from Ohm to Einstein, 2 vols., Chicago: Chicago University Press, 1986, vol. 1, pp. 78–107Google Scholar.

42 Schubring, op. cit. (41), p. 66.

43 Published in Jenaische Allgemeine Literatur-Zeitung (1823) 101–108, pp. 321–383; reprinted in Johann Wolfgang von Goethe, Sämtliche Werke (Münchner Ausgabe), 33 vols., Munich: btb, 2006, vol. 12, pp. 842–904.

44 Hittorf, J. Wilhelm, ‘Rechtfertigung des Satzes: “Electrolyte sind Salze” als Erwiderung auf Dr. L. Bleeckrod's Kritik’, Annalen der Physik und Chemie (1878) 240, pp. 374–416, 401CrossRefGoogle Scholar. Among his teachers who belonged to the founding generation of the seminar's professors were Karl Gustav Bischof (1792–1870, chemistry and technology), Johann Jacob Noeggerath (1788–1877, mineralogy and mining), and Georg August Goldfuss (1782–1848, zoology).

45 Hittorf, op. cit. (44), p. 401.

46 Esenbeck's understanding of Formenlehre and his educational programme is summarized in Nees von Esenbeck, Allgemeine Formenlehre der Natur als Vorschule der Naturgeschichte, Breslau: Leuckart, 1852, p. vi; on Esenbeck see Dietrich von Engelhardt (ed.), Christian Gottfried Nees von Esenbeck. Politik und Naturwissenschaft in der ersten Hälfte des 19. Jahrhunderts, Stuttgart: Wissenschaftliche Verlagsgesellschaft, 2004.

47 Johann Wolfgang von Goethe, ‘The experiment as mediator between object and subject’, in idem, The Collected Works, 12 vols., Princeton: Princeton University Press, 1995, vol. 12 (ed. and tr. Douglas Miller), pp. 11–17, 16.

48 Goethe, , ‘Empirical observation and science’, in idem, The Collected Works, op. cit. (47), vol. 12 , pp. 24–25Google Scholar.

49 In particular – a disturbing aversion for a scientist of the mid-nineteenth century – Hittorf abhorred theories that still referred to speculations in the 31st query of Newton's Opticks: ‘in meiner dritten Mittheilung erklärte ich mich mit aller Entschiedenheit gegen die zur Herrschaft gelangte Theorie, welche Newton in seinem Quaestio XXXI der Optik über das Wesen der chemischen Verbindungen aufgestellt’, Hittorf to Wilhelm Ostwald, 19 November 1892, Berlin-Brandenburgische Akademie der Wissenschaften, Berlin, Wilhelm-Ostwald-Archiv (subsequently WOA), 59/8. For him, this type of chemistry had successfully expelled alchemical thinking in the eighteenth century but it had no value in itself and therefore had to be replaced. Hittorf, J. Wilhelm, ‘Ueber die Wanderung der Ionen während der Elektrolyse, iii’, Annalen der Physik und Chemie (1859) 182, pp. 337–411, 513–586, 579CrossRefGoogle Scholar.

50 In Hittorf's practice many features can be found of what Friedrich Steinle has termed ‘explorative experimentation’. Friedrich Steinle, ‘Exploratives vs. theoriebestimmtes Experimentieren: Ampères erste Arbeiten zum Elektromagnetismus’, in Michael Heidelberger and Friedrich Steinle (eds.), Experimental Essays – Versuche zum Experiment, Baden-Baden: Nomos, 1998; idem, ‘Entering new fields: exploratory uses of experimentation’, Philosophy of Science (1997) 64, pp. 65–74CrossRefGoogle Scholar.

51 Justus von Liebig, ‘Induction und Deduction’, in idem, Reden und Abhandlungen, , Leipzig, 1874, 303; cited from August Wilhelm Hofmann, The Life-Work of Liebig: A Discourse (Faraday Lecture for 1875), London:Macmillan, 1876, p. 70Google Scholar.

52 Hittorf, op. cit. (44), p. 397.

53 For a comparison of ‘experimental’ and ‘measurement’ physics see Jungnickel and McCormmach, op. cit. (41), pp. 120–121; Sichau, Christian, Die Viskositätsexperimente von J.C. Maxwell und O.E. Meyer, Berlin: Logos, 2002, p. 238Google Scholar.

54 Friedrich Paschen in 1925, cited in Edgar Swinne, Friedrich Paschen als Hochschullehrer, Berlin: D.A.V.I.D., 1989, p. 16; on Kundt see Cahan, David, ‘From dust figures to the kinetic theory of gases: August Kundt and the changing nature of experimental physics in the 1860s and 1870s’, Annals of Science (1990) 47, pp. 151–172CrossRefGoogle Scholar, 170.

55 Technical education was a major concern of the government and the university's trustees, who wanted to ‘put industry on a sound scientific footing’ and to make mechanics and physics a ‘common property of every intelligent technician’. W. Ernst, Julius Plücker, Bonn: Scheur, 1933, p. 70–71.

56 Ernst, op. cit. (55), p. 77; on physics at Bonn University see Jungnickel and McCormmach, op. cit. (41), pp. 234–238.

57 Hittorf to Plücker, 11 June 1847, PCNRC, vol. 3, 12.

58 Plücker's research on the magnetic properties of solids and gases was supported by his former student August Beer (Ernst, op. cit. (55), p. 56). Additional support came from his former student Fessel and one of Fessel's apprentices, Epkens, who worked as mechanics and instrument-makers in Bonn and Cologne (Ernst, op. cit. (55), p. 79). In a letter to Justus von Liebig, Geissler complained in 1858 that he had prepared and conducted most experiments while Plücker only mentioned him as a ‘helping hand’ in his publications. Geissler to Liebig, 2 February 1858, Bayerische Staatsbibliothek, Munich, Liebigiana, IIB, Geißler, H.

59 Clebsch, op. cit. (20), p. 33, from a passage in Clebsch's obituary that was written by Hittorf.

60 A short summary of his thesis was published in 1849. Hittorf, J. Wilhelm, ‘Ableitung einiger Eigenschaften der Kegelschnitte aus ihrer Polargleichung’, Journal für die reine und angewandte Mathematik (1849) 38, pp. 89–92CrossRefGoogle Scholar.

61 Hittorf to the minister of religious, educational and medical affairs, Johann Albrecht Friedrich von Eichhorn, 28 February 1847, SPKSD, F1e 1869 (3); primarily Hittorf was sent to Berlin to complete his Habilitation and to take lectures with Dove and the chemists Heinrich Rose and Karl Friedrich Rammelsberg. Hittorf to Plücker, 11 June 1847, PCNRC, vol. 3, 12.

62 He stayed in Münster for the rest of his life and seems to have made a good living. As he reported to Plücker in 1847 his lecture had been visited by forty-nine students and due to the lecture fees he felt ‘as if the golden age has dawned’. Hittorf to Plücker, 22 November 1847, PCNRC, vol. 3, 13.

63 The intended measuring of the resistance or conductivity of various electrolytes was later realized by Kohlrausch, Friedrich. Cahan, David, ‘Kohlrausch and electrolytic conductivity: instruments, institutes, and scientific innovation’, Osiris (1989) 5, pp. 166–185Google Scholar.

64 ‘Die Arbeit, welche der Strom bei der Elektrolyse verrichtet, wenn die Ionen an den Elektroden frei werden, und welche durch die Polarisation angezeigt ist, wird nur zum allerkleinsten Theil auf die Trennung verwendet.’ Hittorf, op. cit. (49), p. 581.

65 Hittorf, J. Wilhelm, ‘Rechtfertigung seiner Mittheilung “Ueber die Wanderung der Ionen”. Elektrolyse einer Lösung zweier Salze’, Annalen der Physik und Chemie (1858) 179, pp. 1–56, 20CrossRefGoogle Scholar.

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67 Particularly strong expressions of his distaste can be found in Hittorf, op. cit. (44); Berzelius, an adherer of chemical atomism, was an avowed enemy of Naturphilosophie, or ‘phosphorism’ as it was called in Sweden. Rocke, Alan J., ‘The reception of chemical atomism in Germany’, Isis (1979) 70, pp. 519–536, 521CrossRefGoogle Scholar.

68 Hittorf to Ostwald, 21 January 1891, WOA, 59/3; in a later letter he renewed his criticism of Clausius's mathematical and theoretical approach: ‘In physics the work of mathematicians has always enjoyed the great advantage of being reckoned infallible even when these mathematicians were lacking practical experience and knowledge in the field and of the subjects they were treating. In my understanding, such an advantage has been responsible for the success of Clausius's publication as well.’ Hittorf to Wilhelm Ostwald, 19 November 1892, WOC, 59/8; Clausius, Rudolf, ‘Ueber die Elektricitätsleitung in Elektrolyten’, Annalen der Physik (1857) 177, pp. 338–360CrossRefGoogle Scholar.

69 Hittorf, op. cit. (44), p. 395.

70 ‘Es ist immer mein lebhafter Wunsch gewesen, der großartigen Metamorphose, welche die Materie an den Elektroden erfährt, eine dem Versuch zugängliche neue Seite abzugewinnen.’ Hittorf to Ostwald, 21 January 1891, WOC, 59/3.

71 ‘Stahl mit seiner phlogistischen Theorie steht meinem Gefühle nach der Wahrheit viel näher als Laplace, Lavoisier und Berthollet, sobald wir das Phlogiston nicht als Materie, sondern als lebendige Kraft deuten.’ Hittorf, op. cit. (44), p. 393. Maybe Hittorf had been inspired by William Odling, who in 1871, in a lecture at the Royal Institution, ‘The revived theory of phlogiston’, presented phlogiston as anticipation of the concept of chemical energy. Knight, David M., ‘The physical sciences and the Romantic movement’, in idem, Science in the Romantic Era, Aldershot: Ashgate, 1998, pp. 78–99, 80Google Scholar. Hittorf was familiar with the German translation of Odling's A Manual of Chemistry, Descriptive and Theoretical, London: Longman, 1861Google Scholar.

72 Hittorf, op. cit. (49), p. 585; Goethe argued in a very similar way: ‘A false hypothesis is better than none at all, for the mere fact that it is false does not harm. But when such a hypothesis establishes itself, when it finds general acceptance and becomes something like a creed open to neither doubt nor test, it is an evil under which centuries to come will suffer. Here Newton's theory may serve as an example.’ Goethe, J.W., ‘Analysis and synthesis’, in idem, op. cit. (47), pp. 48–50, 49Google Scholar.

73 Hittorf, J. Wilhelm, ‘Ueber das elektrische Leitungsvermögen des Schwefelsilbers und Halbschwefelkupfers’, Annalen der Physik und Chemie (1851) 160, pp. 1–29CrossRefGoogle Scholar; Hittorf, J. Wilhelm, ‘Zur Kenntniss des Phosphors’, Annalen der Physik und Chemie (1865) 202, pp. 193–228CrossRefGoogle Scholar. On Heinrich Geissler's experiments see ibid., p. 222; and Schrötter, Anton von, ‘Ueber die Umwandlung des gewöhnlichen Phosphors in amorphen durch Einwirkung der Elektrizität’, Annalen der Physik und Chemie (1874) 228, pp. 171–173Google Scholar.

74 Hittorf, op. cit. (49), p. 345.

75 Heidelberger, Michael, ‘Towards a logical reconstruction of revolutionary change: the case of Ohm as an example’, Studies in History and Philosophy of Science (1980) 11, pp. 103–121, 111CrossRefGoogle Scholar.

76 These terms were used by the French physiologist Guillaume-Benjamin Duchenne to describe his electrophysiological investigations (Siegert, Bernhard, Passagen des Digitalen. Zeichenpraktiken der neuzeitlichen Wissenschaften, 1500–1900, Berlin: Brinkmann & Bose, 2003, p. 352Google Scholar). Beautiful examples for the application of the electric circuit in physiological studies are given in Sven Dierig's study on Emil Du Bois-Reymond: Wissenschaft in der Maschinenstadt. Emil Du Bois-Reymond und seine Laboratorien in Berlin, Göttingen: Wallstein, 2006.

77 Schagrin, Morton L., ‘Resistance to Ohm's law’, American Journal of Physics (1963) 31, pp. 536–547CrossRefGoogle Scholar.

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79 Lodge, Oliver, ‘Modern views of electricity, ii’, Nature (1887) 36, pp. 582–585, 583CrossRefGoogle Scholar.

80 Lodge, op. cit. (79). In 1887, though, the technical standards had considerably improved in comparison to the 1850s and 1860s. On the standardization of the ohm see Simon Schaffer, ‘Late Victorian metrology and its instrumentation: a manufactory of Ohms’, in Robert Bud und Susan E. Cozzens (eds.), Invisible Connections: Instruments, Institutions and Science, Bellingham: SPIE, 1992, pp. 23–56; Hunt, Bruce, ‘The ohm is where the art is: British telegraph engineers and the development of electrical standards’, Osiris (1993) 9, pp. 48–63CrossRefGoogle Scholar, Kathryne M. Olesko, ‘Precision, tolerance, and consensus: local cultures in German and British resistance standards’, in Jed Z. Buchwald (ed.), Scientific Credibility and Technical Standards in 19th and Early 20th Century Germany and Britain, Dordrecht: Kluwer, 1996, pp. 117–156.

81 In Hittorf's understanding, Faraday had already shown the applicability of Ohm's law to electrolytic conduction in his early studies without knowing the law itself. Hittorf, J. Wilhelm, ‘Ueber die Wanderung der Ionen während der Elektrolyse, i’ Annalen der Physik und Chemie (1853) 165, pp. 177–211CrossRefGoogle Scholar, 178.

82 Plücker, Julius and Hittorf, J. Wilhelm, ‘On the spectra of ignited gases and vapours, with especial regard to the different spectra of the same elementary gaseous substance’, Philosophical Transactions of the Royal Society (1865) 155, pp. 1–29CrossRefGoogle Scholar; the paper was already read in 1864 but it took several months to prepare the lithographic plates; for more information on the production process, the lithographer Aimé Henry, and the negotiations with the journal's editors see Hentschel, op. cit. (7), pp. 127–29; on the further development and influence of the discovery of double spectra see McGucken, William, Nineteenth-Century Spectroscopy: Development of the Understanding of Spectra 1802–1897, Baltimore: Johns Hopkins University Press, 1969, pp. 53–73Google Scholar; on Gestalt versus ‘absolute measures and complete catalogues’ see Hentschel, op. cit. (7), p. 51.

83 This misconception was resolved in the mid-1870s when experiments by other researchers showed that temperatures inside the positive light and close to the anode were below 100°C and Hittorf began searching for a direct impact of electricity on the material constitution.

84 Plücker and Hittorf, op. cit. (82), p. 1, p. 4; on other occasions, Hittorf praised the electric current as a suitable and powerful tool in chemical practice: ‘For those who are familiar with its laws, [the electric current] is a much more amenable and powerful agent than heat.’ Hittorf, J. Wilhelm, ‘Die unorganische Chemie und ihre Pflege’, Zeitschrift für Elektrochemie (1899) 2, pp. 27–33, 29CrossRefGoogle Scholar. Hittorf was particularly interested in the targeted modification and transformation of materials: ‘Der electrische Strom, welcher an den Elektroden für jedes Ion diese ausserordentliche Metamorphose, diesen grossartigen Zustandswechsel bewirkt, muss zum mächtigsten Hülfsmittel der Forschung werden, wenn sie einst diesen Vorgang an den Elektroden dem Wesen nach besser wie heute ergründet hat, und infolge davon modificierend in denselben eingreifen kann.’ Hittorf, op. cit. (44), p. 394.

85 Verhandlungen des naturhistorischen Vereins der preussischen Rheinlande und Westphalens (1863) 20, p. 40.

86 Exceptions were Eugen Goldstein from the mid-1870s and William Crookes from late 1878 onwards. For example, J.J. Thomson showed no particular interest in the processes at the cathode or in cathode rays before 1896. Falconer, Isobel, ‘Corpuscles, electrons and cathode rays: J.J. Thomson and the “discovery of the electron”’, BJHS (1987) 20, pp. 241–276CrossRefGoogle Scholar, 253.

87 ‘Wenn die Ursache der räthselhaften Schwächung, welche die Entladung in der Umgebung der Kathode erleidet, Widerstand genannt wurde, so veranlaßt dieß die Uebereinstimmung, die … zwischen ihrem Verhalten und demjenigen des gewöhnlichen Leiters in der Strombahn nachgewiesen wurde. Dabei müssen wir uns jedoch des wesentlichen Unterschiedes bewußt bleiben, daß in dem Gase dieselben Theilchen, je nachdem sie an der positiven oder negativen Electrode liegen, so äußerst verschiedene Hindernisse bereiten, eine Thatsache, für welche weder bei den Metallen, noch den Elektrolyten eine Analogie besteht.’ Wilhelm Hittorf, J., ‘Ueber die Electricitätsleitung der Gase, iii’, Annalen der Physik und Chemie (1879) 243, pp. 553–631, 223Google Scholar.

88 Hittorf, J. Wilhelm, ‘Ueber die Elektricitätsleitung der Gase’, Annalen der Physik und Chemie (1869) 212, pp. 1–31, 197–234, 1CrossRefGoogle Scholar.

89 ‘[E]s ist nicht unmöglich, daß die Gase auf unserem Gebiete, wie in der Lehre von der Wärme, am leichtesten das Wesen der Erscheinungen erkennen lassen’. Hittorf, op. cit. (88), p. 223.

90 For a detailed account of Hertz's gas discharge experiments, see Buchwald, Jed Z., The Creation of Scientific Effects: Heinrich Hertz and Electric Waves, Chicago: University of Chicago Press, 1994, pp. 131–174, 142–150CrossRefGoogle Scholar for Hertz’ experiments on intermitted or continuous discharge; idem, ‘Why Hertz was right about cathode rays’, in idem, op. cit. (40) pp. 151–169.

91 Darrigol, op. cit. (1), p. 285.

92 Williams, op. cit. (31), p. 478.

93 Hittorf, op. cit. (88), p. 10.

94 Hittorf, op. cit. (88).

95 ‘Letzterer ist … dadurch bedingt, dass das Molecül die Energie, welche der Strom ihm zuführt, in derselben Zeit durch Leitung und Strahlung an die Umgebung verliert. Wir können jeden der vorangegangenen Zustände der Leitungsfähigkeit als Grenzwerth fixiren, indem wir die Stromstärke durch Aufnahme eines passenden Widerstandes vermindern’. Hittorf, op. cit. (87), p. 624; idem, ‘Ueber die Electricitätsleitung der Gase, iv’, Annalen der Physik und Chemie (1883) 256, pp. 705–755CrossRefGoogle Scholar, 721.

96 ‘[E]in Zustand der Spannung, in welchem das Bestreben der Molecüle, den Zwangszustand der Polarisation zu verlassen und in den gewöhnlichen zurückzukehren’. Hittorf, op. cit. (87), p. 624.

97 Buchwald, Jed Z., From Maxwell to Microphysics, Chicago: University of Chicago Press, 1985, p. 32Google Scholar.

98 ‘Die mathematischen Arbeiten, bei welchen die gewohnte Bewegung dem Körper entzogen war, schädigten meine Gesundheit so, daß ich vor vier Jahren ein Semester feiern … musste.’ Hittorf to the minister of religious, educational and medical affairs, 3 October 1884, SPKSD, F1e 1869 (3).

99 Recollections of Adelheid Sturm, Lebenserinnerungen einer Professorenfrau, Breslau, 1911; translated from Heydweiller, Adolf, ‘Johann Wilhelm Hittorf’, Physikalische Zeitschrift (1915) 9–10Google Scholar, p. 175; on the problematic reception of Maxwell's Treatise see Andrew Warwick, ‘“A very hard nut to crack”, or making sense of Maxwell's Treatise on Electricity and Magnetism in mid-Victorian Cambridge’, in Mario Biagioli and Peter Galison (eds.), Scientific Authorship: Credit and Intellectual Property in Science, London: Routledge, 2002, pp. 133–164.

100 William Thomson, ‘Presidential address’ (1871), in George Basalla, William Coleman and Robert H. Kargon (eds.), Victorian Science: A Self-Portrait from the Presidential Addresses of the British Association for the Advancement of Science, Garden City, NY: Anchor Books, 1970, p. 108. This situation did not change much with Maxwell's immediate followers: ‘The Maxwellian goal was to create a theory of electromagnetism which made no use what so ever of the microstructure of matter … For the Maxwellians, the world was fundamentally a continuum, and the laws which governed it had to be expressed in an appropriate mathematical form (the discrete structure of matter had, they felt, to be explained as an emergent property of the underlying continuum).’ Buchwald, op. cit. (97), p. 23.

101 Thomson, Joseph John, Notes on recent Researches in Electricity and Magnetism, Oxford: Clarendon Press, 1893, p. 69Google Scholar.

102 Thomas Romney Robinson, 4 April 1864, report on Plücker and Hittorf, op. cit. (82), Archive of the Royal Society, RR.5.186.

103 In 1897, the completion of a battery of ten thousand elements by John Trowbridge in Harvard was still considered a major event: ‘For many years thereafter, the battery was a famous and unique Harvard fixture, attracting researchers from far and wide.’ Lawrence Aronovitch, ‘The spirit of investigation: physics at Harvard University, 1870–1910’, in Frank A.J.L. James (ed.), The Development of the Laboratory: Essays on the Place of Experiment in Industrial Civilization, London: Macmillan, 1989, p. 98.

104 On the construction of his battery, Heinrich Hertz reported in 1882 to his parents, ‘I am labouring just like a factory worker, for I have to repeat every action a thousand times, so that for hours at a time I do nothing but bore one hole after another, bend one metal strip after another, spend hours varnishing them one by one, etc.’ Heinrich Hertz, Memoirs, Letters, Diaries, 2nd edn (ed. Johanna Hertz, tr. L. Brinner, Mathilde Hertz and Charles Susskind), San Francisco and Weinhein: Physik Verlag, 1977, p. 167.

105 Hittorf, op. cit. (88), p. 224.

106 Hittorf to Plücker, 1 February and 1 March 1863, PCNRC, vol. 3, letters 16 and 17.

107 Hittorf to Plücker, 24 May 1863 and 1 June 1863, PCNRC, vol. 3, 18.

108 Hittorf to Plücker, 8 June 1863, PCNRC, vol. 3, 19.

109 Hittorf to Plücker, 20 January 1867, PCNRC, vol. 3, 30; in the 1890s J.J. Thomson's assistant Robin Strutt reported similar experiences with ‘bewitched’ glass. Edward Arthur Davis and Isobel Falconer (eds.), J.J. Thomson and the Discovery of the Electron, London: Taylor and Francis, 1997, p. 54.

110 The use of platinum wire was quite common; the additional use of layers of different types of glass seems to have been suggested by Hittorf's local glass-blower, Schertiger. Hittorf, op. cit. (88), p. 199.

111 Thomas Romney Robinson, 4 April 1864, report on Plücker and Hittorf, op. cit. (82), Archive of the Royal Society, RR.5.186; interestingly Hittorf's name is not mentioned at all by Robinson.

112 ‘With a former letter Dr. Hittorf sent me an evacuated tube which does not permit the discharge neither of Ruhmkorff's smaller coil nor of a Leyden jar. I intended to send it to you when I have opportunity.’ Plücker to Stokes, 21 March 1865, Cambridge University Library, Stokes Collection (subsequently CULSC), P 399.

113 ‘Da Gassiot schon seit Jahren dieses Problem in seinen Arbeiten verfolgt, und bei den großartigen, ihm zur Verfügung stehenden Mitteln so viele Vortheile genießt, so würde ich, wenn ich ihm die Vacuum-Röhren lieferte, alles aus der Hand geben und auf ein Resultat der Arbeit, die mir viel Zeit gekostet, verzichten müssen.’ Hittorf to Plücker, 31 January 1867, PCNRC, vol. 3, 31.

114 John Peter Gassiot to Plücker, 5 September 1866, PCNRC.

115 Hittorf, op. cit. (88), pp. 202 and 211.

116 Wüllner, Adolf, ‘Ueber die erste Darstellung absolute luftleerer Röhren’, Annalen der Physik und Chemie (1868) 133, pp. 509–510Google Scholar; Hittorf to Oskar v. Miller, 20 November 1904, Archive of the Deutsches Museum, Munich (subsequently DMM), HS 576.

117 William Crookes to George Gabriel Stokes, 19 April 1876, CULSC, C 1091.

118 On the development of Crookes's vacuum technology and Geissler's (and accordingly Hittorf's) influence see Müller, op. cit. (6), pp. 176–205.

119 , Plücker, ‘Fortgesetzte Beobachtungen über die elektrischen Entladungen’, Annalen der Physik und Chemie (1858) 181, pp. 67–84, 69CrossRefGoogle Scholar.

120 Hertz reported on his pumping labour in 1882: ‘a real exertion over the long run; I occasionally had to interrupt the experiments out of sheer physical exhaustion’. Heinrich Hertz to his parents, 10 July 1882, in Heinrich Hertz, Memoirs, Letters, Diaries, op. cit. (104), p. 167.

121 By many nineteenth-century researchers physical and intellectual education were perceived as complementary activities. Dierig, op. cit. (76), pp. 122–144; Andrew Warwick, Masters of Theory: Cambridge and the Rise of Mathematical Physics, Chicago: University of Chicago Press, 2003.

122 ‘Wie ich fürchte, wird die neue Geometrie nicht ohne Schuld in Bezug auf Ihr Befinden seyn. Sie zwingt zur sitzenden Lebensweise! Möge sie bald abschließen und die Beschäftigung mit der Physik wiederkehren, mit welcher körperliche Bewegung und Anstrengung verbunden ist.’ Hittorf to Plücker, 19 December 1865, PCNRC, vol. 3, 25.

123 Hittorf, op. cit. (88), p. 201; idem, op. cit. (73), p. 196.

124 Hittorf to Plücker, 31 January 1867, PCNRC, vol. 3, 30.

125 A collection of his tubes – most of them reconstructed by Hittorf in 1904, others sent to the Museum by Hittorf's successor in Münster – can be found in the Deutsches Museum (Hittorf to Oskar v. Miller, 18 December 1904, DMM, HS 1939/46 (1); Gerhard Schmidt to Deutsches Museum, DMM, VA 1840 and 1843). Hittorf's instruments at the Deutsches Museum and his correspondence with members of the museum are listed in Bernhard Taufertshöfer, ‘Johann Wilhelm Hittorf und das Deutsche Museum’, unpublished diploma thesis, Heidelberg, 2000.

126 In the early 1880s Hittorf managed to reduce the resistance to a minimum by galvanically heating up an iridium electrode with a platinum wire; probably this was the first application of a thermionic cathode. Hittorf, , ‘Ueber die Electricitätsleitung der Gase’, Annalen der Physik und Chemie (1884) 257, pp. 90–139CrossRefGoogle Scholar, 133.

127 Hittorf, op. cit. (87), p. 617.

128 Hittorf, op. cit. (88), p. 3.

129 ‘Wichtig für unsere Einsicht in den Leitungsvorgang der Gase müssen quantitative Bestimmungen der Wärmemengen und Lichtintensitäten werden, welche ein constanter Strom der galvanischen Kette in einem der Masse und den Dimensionen nach unveränderlich bleibendem Gas in der Zeiteinheit erzeugt.’ Hittorf, op. cit. (87), p. 628.

130 Hittorf, op. cit. (87), p. 581.

131 Various authors acknowledged the importance of these results but obviously could not make anything out of them: ‘Hittorf's investigation on what has been called the “resistance” of different parts of a vacuum tube during the discharge has not been mentioned, although it led to results of much interest, which must come to be of great importance when the clue to an explanation of the whole phenomena has been found.’ Chrystal, op. cit. (78), p. 65.

132 Interestingly, Crookes did not mention the negative charge of the ‘radiant matter’ in his first publication on this subject, the Bakerian Lecture in 1878. Instead he wrote, ‘Setting up an intense excitement in a disk of metal by electrical means produces a molecular disturbance which affects the surface of the disk and the surrounding gas’. Crookes, William, ‘On the illumination of lines of molecular pressure, and the trajectory of molecules’, Transactions of the Royal Society (1879) 170, pp. 135–164, 139Google Scholar. In subsequent publications he conceived cathode rays as a stream of negatively charged corpuscles. On Crookes's science and life see Brock, William H., William Crookes (1832–1919) and the Commercialization of Science, Aldershot: Ashgate, 2008Google Scholar.

133 Wiedemann, Gustav and Rühlmann, Richard, ‘Ueber den Durchgang der Elektricität durch Gase’, Annalen der Physik und Chemie (1872) 145, pp. 235–258 and 364–398CrossRefGoogle Scholar.

134 On the transition of Crookes's radiometer research to radiant matter see Müller, op. cit. (6), pp. 206–254.

135 Beginning in the late nineteenth century, scientists and historians considered Hittorf to be an adherent of the so-called ether wave theory of cathode rays (e.g. William Thomson to G.G. Stokes, 1896, in David B. Wilson (ed.), The Correspondence between George Gabriel Stokes and Sir William Thomson, Baron Kelvin of Largs, 2 vols., Cambridge: Cambridge University Press, 1990, vol. 2, p. 632); Hittorf mentioned the wave-like character of the negative light only once – but this single appearance sufficed to classify him as the precursor or even follower of this theory. Hittorf wrote about the Glimmlicht in 1869: ‘Bei derselben sind die Theilchen der negativen Oberfläche Ausgangspunkt einer Bewegung, welche im gasförmigen Medium gleichmäßig nach allen Seiten, strahlenartig sich ausbreitet und darin mit der Wellenbewegung übereinstimmt.’ Hittorf, op. cit. (88), p. 222. Later he no longer mentioned the surface of the cathode as source of some of the ray-like effects but only mentioned that ‘very hot but hardly luminous’ gaseous molecules emit light of a very high refraction index which was responsible for the fluorescence of the glass wall. Hittorf, op. cit. (87), p. 586.

136 Christoph Meinel, Karl Friedrich Zöllner und die Wissenschaftskultur der Gründerzeit. Eine Fallstudie zur Genese konservativer Zivilisationskritik, Berlin: SIGMA, 1991; on the conflict between Helmholtz and Zöllner see Jed Z. Buchwald, ‘Electrodynamics in context: object states, laboratory practice, and anti-Romanticism’, in David Cahan (ed.), Hermann von Helmholtz and the Foundation of Nineteenth-Century Science, Berkeley: University of California Press, 1993, pp. 334–373; the third volume of Zöllner's collected papers (Die Transzendentale Physik und die sogenannte Philosophie, Leipzig, 1879) was dedicated to Crookes.

137 See the paragraph ‘Bestätigung der elektrischen Emissionstheorie durch die neuen Experimente von Professor Crookes’, in Friedrich Zöllner, Das Skalenphotometer. Ein neues Instrument zur mechanischen Messung des Lichts, Leipzig: Staackmann , 1879, pp. 52, 74–75.

138 Among others, Hittorf's successor in Münster, Gerhard Schmidt, emphasized that Hittorf aimed at an electrolytic understanding of gaseous conduction – at least for the conduction process connected to the positive light (Schmidt, Gerhard C., Die Kathodenstrahlen, Braunschweig: Vieweg, 1907, pp. 28–29Google Scholar); on the further application of electrolytic concepts to gas discharge, particularly by Arthur Schuster, see Darrigol, op. cit. (1), pp. 288–291. Due to his education, Schuster was able to mediate between Weber's, Helmholtz's and Maxwell's electrodynamic theories; Helmholtz's ‘relational physics’ – his attempt to combine field theory with Weberian electrodynamics (Buchwald, op. cit. (136)) – left no obvious traces in Hittorf's work.

139 , Hittorf, ‘Ueber die Elektricitätsleitung der Gase, ii’, Annalen der Physik (1874), Jubelband, 430–445Google Scholar.

140 ‘Ich hoffe für die Electricitätsleitung der Gase … neue Tatsachen und Gesichtpunkte bald bringen und zeigen zu können, dass auch hier blos die Materie des Gases und keine besonderen Fluida in betracht kommen … Vermag ich nicht zwei elektrische Fluida als Träger der Erscheinungen anzunehmen, so kann ich noch weniger einem derselben oder dem Aether der Optik diese Rolle zuerkennen.’ Hittorf, op. cit. (44), p. 397. In 1883 he emphasized this point of view: the gas molecules ‘are the exclusive carriers of conduction and I don't think … we can conceive the hypothetical ether as the carrier of this process’. , Hittorf, ‘Ueber die Electricitätsleitung der Gase, iv’, Annalen der Physik (1883) 256, pp. 705–755, 735CrossRefGoogle Scholar.

141 , Hittorf, ‘Berichtigung zu dem Aufsatze. Ueber die Elektricitätsleitung der Gase’, Annalen der Physik und Chemie (1879) 243, p. 671Google Scholar; cf. Hiebert, op. cit. (1), p. 133 n. 68.

142 Hittorf to Ostwald, 27 December 1901, WOC, 59/24.