1. A more detailed discussion of this topic may be found in my paper ‘Boltzmann's influence on Lorentz H.A.International Symposium on Ludwig BoltzmannRome 1989 February 9 11 to appear in the proceedings of the the contents of the correspondence between Boltzmann and Lorentz and their personal relationship are discussed in A. J. Kox, ‘The correspondence between Boltzmann and H. A. Lorentz’, inLudwig Boltzmann: Internationale Tagung anlässlich des 75. Jahrestages seines Todes, 5–8 September 1981, Ausgewählte Abhandlungen, edited by R. Sexl and J. Blackmore (Graz and Brunswick, 1982), pp. 73–86; volume v ofLudwig Boltzmann: Gesamtausgabe, edited by R. Sexl, to be published. All letters to Lorentz that I quote in this paper are in the Lorentz Archive at the Dutch State Archives (‘Algemeen Rijksarchief’) in the Hague. The original letters from Lorentz to Boltzmann are in the possession of Boltzmann's heirs. The letters from Lorentz to Korteweg are part of the collection of the University Library of the University of Amsterdam. In these footnotes the following abbreviations are used:Abh., H. A. Lorentz,Abhandlungen über theoretische Physik(Leipzig, Berlin, 1906–7);C.P., H.A. Lorentz,Collected Papers, edited by P. Zeeman and A. D. Fokker, 9 vols (The Hague, 1934–9);W. A., L. Boltzmann,Wissenschaftliche Abhandlungen, edited by F. Hasenöhrl, 3 vols (Leipzig, 1909).