Few working papers survive from the period when Maxwell was working on “Physical Lines.” My own search of relevant archives, as well as the more exhaustive search conducted by Peter Harman in connection with his edition in progress of The Scientific Letters and Papers of James Clerk Maxwell, 3 vols. (Cambridge University Press, 1990–), turned up nothing beyond the material to which attention is directed by A. E. B. Owens's handlist to Add. MSS 7655 at the University Library, Cambridge. Of a set of five folios constituting Add. MSS 7655, V, c/8, two folios clearly correspond to the period when Maxwell was working on “Dynamical Theory” (see Appendix 2), and a third, dealing with “Helmholtz's Wirbelfäden [Vortex Filaments],” appears to date from a later period as well (1864–70 – Peter Harman, private communication; see also Letters and Papers of Maxwell, 2). The two remaining folios (both blank verso) evidently are associated with “Physical Lines.” One of these clearly relates to the treatment of motional electromotive forces that appears in “Physical Lines,” Part II, 476–85; this draft fragment refers explicitly to “equations (55),” which appear on p. 476 of the published version, and arrives at a form of the published equations (77), on p. 482.

The remaining folio is quite informative concerning various aspects of Maxwell's work on the molecular-vortex model; a photograph of it is presented in Fig. A 1.1, and I here transcribe it in full (cf. also the transcription in Harman, ed., Letters and Papers of Maxwell, 1 693).