¹ This is of course a modern distinction. As we shall see, not all of Franklin's followers would have accepted it.

² Except where otherwise stated, all references to Franklin's electrical writings are to his Experiments and observations on electricity, made at Philadelphia in America in the edition prepared by I. Bernard Cohen and entitled Benjamin Franklin's experiments (Cambridge, Mass., 1941Google Scholar). Hereafter this work will be cited as Experiments.

³ Experiments, Letter II, pp. 171–8.Google Scholar

⁴ Ibid., p. 172.

⁵ Ibid., p. 177.

⁶ Ibid., Letter III, p. 182.

⁷ Ibid., p. 185.

⁸ In this his procedure was in sharp contrast with that of most of his predecessors; indeed, a strong case could probably be made in support of the claim that it was precisely at this point that Franklin took the crucial step towards his novel theoretical views. It might be added that one reason why Franklin paid so little attention in his early work to attractions and repulsions was that generally he did not have recourse to them to test whether or not a body was electrified at any particular stage of an investigation; except in the case mentioned above, he almost invariably tested bodies for electrification by seeing whether he could draw a spark from them.

⁹ Experiments, p. 199Google Scholar. To be sure, Franklin described this result as one ‘which surprises us, and is not hitherto satisfactorily accounted for’, which could be taken to imply that he felt he had satisfactorily accounted for the other cases of attraction and repulsion. However, in view of his total failure up to this point to provide any theoretical discussion of these other cases, I prefer to interpret his remark as meaning only that whereas it was reasonable to suppose that an accumulation of fluid might give rise to such forces, it was surprising that an absence of fluid (that is, an absence of a cause) could do so.

¹⁰ Ibid., p. 202. Franklin himself emphasized the point I am making, for in support of his assertion he added:

‘Thus the stream of a fountain, naturally dense and continual, when electrified, will separate and spread in the form of a brush, every drop endeavouring to recede from every other drop. But on taking out the electrical fire they close again.’

¹¹ Ibid., pp. 213–36. The covering letter which accompanied the paper was dated 29 July 1750.

¹² Ibid., p. 213.

¹³ He did so in the following terms:

‘Thus common matter is a kind of spunge to the electrical fluid. And as a spunge would receive no water if the parts of water were not smaller than the pores of the spunge; and even then but slowly, if there were not a mutual attraction between those parts and the parts of the spunge; and would still imbibe it faster, if the mutual attraction among the parts of the water did not impede, some force being required to separate them; and fastest, if, instead of attraction, there were a mutual repulsion among those parts, which would act in conjunction with the attraction of the spunge. So is the case between the electrical and common matter’. (Ibid.)

¹⁴ At one stage Franklin did make a very cursory remark which might be taken to be somewhat equivocal on this point, for immediately after stating that the particles of electrical matter mutually repelled each other, he added: ‘Hence the appearing divergency in a stream of electrified effluvia’. (Ibid.) If this was a reference to his earlier experiment with a stream of water emerging from an electrified fountain (see note 8), it must stand as an instance in which he did not feel it necessary to invoke electrical atmospheres to explain a macroscopic repulsion. On the other hand, it is more likely that Franklin was referring to the apparent divergence (visible in a darkened room) of the discharge from a pointed conductor, for in his original manuscript he had written of the divergency in a stream of ‘electrical’ rather than ‘electrified’ effluvia (The papers of Benjamin Franklin [New Haven: Yale University Press, 1959—in progress], iv. 10Google Scholar); furthermore, he had included at this point the footnote referring to John Ellicott's paper in the Philosophical transactions of the Royal Society which was transferred in the published version to the end of the next section, and Ellicott had argued at one point in his paper that ‘the Existence of these Effluvia is proved by all those Experiments in which a Stream of Light is seen to issue from the electrified Body; particularly those Streams which are seen to issue in diverging Rays from the End of the original Conductor, when made of Metal, and reduced to a Point’ (Philosophical transactions, xlv [1748], 196Google Scholar). In this case it would have been the actual repulsion between the particles which was being observed, and no recourse to atmospheres would have been expected anyway. Even if it was the fountain experiment to which Franklin was referring, however, the emphasis on atmospheres in the rest of the paper, and in succeeding papers as well, is overwhelming.

¹⁵ Experiments, p. 214.Google Scholar

¹⁶ The analogy was closer in the eighteenth century than it would be today, for, following Newton, Franklin and his contemporaries regarded air too as being made up of mutually repelling particles.

¹⁷ Experiments, p. 216.Google Scholar

¹⁸ Ibid., p. 207.

¹⁹ Ibid., p. 233.

²⁰ Ibid., p. 216. The emphasis is mine.

²¹ Ibid.

²² Ibid., p. 233.

²³ Ibid., p. 213.

²⁴ There are certain dangers in choosing to ignore Franklin's statement about the evacuated tube, for in a later discussion of the relation between an electrical atmosphere and air he made an identical remark:

‘Dry air assists in confining the electrical atmosphere to the body it surrounds, and prevents its dissipating: for in vacuo it quits easily, and points operate stronger … Yet an electric atmosphere and air do not seem to exclude each other, for we breathe freely in such an atmosphere, and dry air will blow through it without displacing or driving it away … An electrical atmosphere raised round a thick wire, inserted in a phial of air, drives out none of the air, nor on withdrawing that atmosphere will any air rush in.’ (Ibid., p. 248.)

Similar remarks recur throughout the later letters. Perhaps the safest conclusion to draw is that Franklin himself did not fully appreciate the dangers to his whole concept of atmospheres inherent in such remarks.

²⁵ Ibid., p. 302.

²⁶ Ibid. Since mixing would only become a problem once contact between the two masses of fluid had occurred, Franklin's concern here to rule it out as a possibility confirms that it was indeed actual contact between the two masses of fluid that he had in mind as the cause of their mutual repulsion.

²⁷ Ibid.

²⁸ Ibid., p. 349.

²⁹ Ibid., p. 365. Does Franklin's admission that attraction was ‘unintelligible’ mean that he was by then (1762) aware of the problems his theory confronted even in accounting for attractions, or is it simply a recognition that all the forces he had invoked lacked a ‘mechanical’ explanation of the Cartesian kind?

³⁰ St Petersburg, 1759.

³¹ In a very real sense, then, the action-at-a-distance theory of electricity was due to Aepinus and not to Franklin (a point that has been made already by Whittaker, E. T. in his classic History of the theories of aether and electricity [London, 1910], p. 48Google Scholar). On the other hand, Franklin's forces between particles were probably not confined in their action to microscopic distances, since his atmospheres extended to considerable distances around charged bodies, and the particles in their outermost layers were apparently still held in place by the attraction of the particles of ordinary matter at the centre. It therefore becomes even less clear why Franklin thought it necessary to invoke atmospheres at all, but invoke them he certainly did.

³² See, for example, the report in the Gentleman's magazine of the dispute in Paris between Nollet and the Franklinist LeRoy, Jean Baptiste (Gentleman's magazine, xxix [1759], 319Google Scholar), as also LeRoy's own definition of his terms, as set out in the title of his initial contribution to the debate: ‘Mémoire sur l'électricité, où l'on montre par une suite d'expériences, qu'il y a deux espèces d'électricités, l'une produite par la condensation du fluide électrique, & l'autre par sa raréfaction; & qu'elles ont chacune des phénomènes particuliers qui les caractérisent parfaitement’ (Histoire de l'Académie Royale des Sciences [1753], Mémoires, p. 447Google Scholar). Professor Russell McCormmach has drawn attention, in a somewhat different context, to the tendency of Franklin, 's supporters to talk in terms of densities, in his unpublished Ph.D. dissertation ‘The electrical researches of Henry Cavendish’ (Case Western Reserve University, 1967).Google Scholar

³³ The best-known instance of this is Ebenezer Kinnersley's remark in a letter to Franklin (Experiments, p. 350Google Scholar), when referring to the electrical fluid, that ‘it [is] one of the established laws of this fluid, that quantities of different densities shall mutually attract each other, in order to restore the equilibrium’. Other cases are described later in this paper. Kinnersley's ‘law’ evoked from Franklin the response that ‘what you give as an established law of the electric fluid … is, I think, not well founded, or else not well expressed’. (Ibid., p. 367.) That Franklin, by then living in London, was aware of how his ideas had been re-interpreted by some of his followers, is indicated by his comment (following a re-statement of his own views): ‘But this you jokingly call “electrical orthodoxy”. It is so with some at present, but not with all; and, perhaps, it may not always be orthodoxy with any body’. (Ibid., p. 368.)

³⁴ Watson, William, Philosophical transactions, xlv (1748), 100.Google Scholar

³⁵ Cohen, I. Bernard has pointed out in his Franklin and Newton (Philadelphia: American Philosophical Society, 1956), p. 443Google Scholar, that we have no record of any account by Watson which would fit the date of ‘Very early last spring’ that Watson gave for the elaboration of his own views. It seems unlikely, however, that any such account would have differed significantly from that which he had given in October 1746 (Philosophical transactions, xliv [1746–1747], 704–49Google Scholar), and so I have based my analysis on the latter.

³⁶ Watson, , op. cit. (35), pp. 738–9Google Scholar. Cohen, has argued (op. cit. [35], pp. 445–9Google Scholar) that the theories differed in other respects as well.

³⁷ Experiments, p. 174.Google Scholar

³⁸ Watson, , Philosophical transactions, xlvii (1751–1752), 210.Google Scholar

³⁹ See Watson's review of Nollet, 's Lettres sur l'électricité (Paris, 1753Google Scholar) in Philosophical transactions, xlviii (1753–1754), 201–26.Google Scholar

⁴⁰ Canton, 's paper was published initially in Philosophical transactions, xlviii (1753–1754), 350–8CrossRefGoogle Scholar. It was subsequently reprinted in Experiments, pp. 293–9, and my citations are to the latter source.

⁴¹ Experiments, p. 294.Google Scholar

⁴² Ibid.

⁴³ Ibid., p. 295.

⁴⁴ Canton, , Philosophical transactions, xlviii (1753–1754), 780–2.CrossRefGoogle Scholar

⁴⁵ Canton, , Philosophical transactions, li (1759–1760), 403Google Scholar. It needs to be emphasized that Canton was talking at this point about the charges developed on the stone, not the process whereby those charges were developed.

⁴⁶ Priestley, Joseph, The history and present state of electricity (London, 1767), p. 263Google Scholar; the emphasis is mine. Priestley's ‘now’ provides confirmation, of course, that Canton had thought earlier that the atmospheres were composed of ‘effluvia’. Furthermore, his characterization of Canton's earlier ideas in terms of ‘effluvia from excited … bodies’ shows that in representing those ideas as fundamentally dynamical we have understood Canton's earlier discussions correctly.

⁴⁷ See below, note 59.

⁴⁸ Priestley, , op. cit. (46), pp. 246–63Google Scholar. Canton certainly knew of Aepinus's work, and Priestley was aware of this, since the latter, in preparing his History, used a copy of the Tentamen which he had borrowed through Canton; indeed, Canton may even have recommended the book to him in the first place. I discuss these and some related points in my paper ‘Aepinus and the British electricians: the dissemination of a scientific theory’, Isis, Ixiii (1972), 190–204.Google Scholar

⁴⁹ Nollet, , Lettres sur l'électricité (Paris, 1753), p. 63.Google Scholar

⁵⁰ Canton at least seems not to have fallen into this latter trap; see the passage from Experiments, p. 294Google Scholar, quoted above, p. 142.

⁵¹ Beccaria, Giambatista, Dell' elettricismo artificiale e naturale (Turin, 1753)Google Scholar. Beccaria's ideas became available to a rather wider audience when a long summary of his views was published in French a few months later under the title Lettre sur l'électricité, par le R. P. J. B. Beccaria… (Paris, 1754).Google Scholar

⁵² Franklin himself was very favourably impressed by Beccaria's book, and upon its appearance he abandoned his own plans for composing a formal reply to Nollet's onslaught on his theory; apparently he regarded Beccaria's efforts as definitive (Experiments, p. 307Google Scholar; see also Pace, Antonio, Benjamin Franklin and Italy [Philadelphia: American Philosophical Society, 1958], pp. 49–53).Google Scholar Similarly, DeLor, who prepared the translation and arranged for the publication of Beccaria's Lettre, remarked in his ‘Avertissement’ to that work that he had been preparing a defence of Franklin's views but had abandoned his plans when he had found that Beccaria had already done so ‘d'une maniére bien supérieure à ce que j'aurois pu faire, & tout-à-fait conforme aux principes que j'avois embrassés'. He had therefore contented himself with making the latter's views available to French readers (Lettre, pp. vi–vii).Google Scholar One cannot help wondering whether Franklin's acquiescence (at this stage at least) in Beccaria's dynamical theory was intended—or had he simply not paid sufficient attention to what Beccaria was saying?

⁵³ Beccaria, , Dell' elettricismo, p. 17Google Scholar; the emphasis is mine. The original Italian reads: ‘ogni segno elettrico avvenga pel vapore, che da un corpo, in cui è in quantità maggiore si espande nell’ altro, in cui è in minore quantità’.

⁵⁴ Ibid., p. 40.

⁵⁵ Ibid.

⁵⁶ Ibid., pp. 26–8.

⁵⁷ Dell' elettricismo. Lettere di Giambattista Beccaria … dirette al chiarissimo sig. Giacomo Bartolomeo Beccari… (Bologna, 1758).Google Scholar

⁵⁸ Ibid., pp. 4–5.

⁵⁹ Ibid., p. 12. Some years afterwards both Priestley, (op. cit. [46], p. 262Google Scholar) and Beccaria himself (Elettricismo artificiale [Turin, 1772], p. 173) claimed priority for the latter, over Aepinus, as the first person to abandon belief in Franklinian-style atmospheres—though Priestley at least refused to commit himself absolutely at this point and inserted the word ‘probably’ in his account. In support, both men referred to ‘Elettricismo artificiale, p. 54’, which can only refer to Book I of Beccaria's Dell' elettricismo artificiale e naturale of 1753. The relevant passage is somewhat obscure but does not really support the claim; and neither does the explanation (noted above) of the mutual repulsion of two equally charged bodies, which had been given only a few pages earlier. Quite apart from this, however, Beccaria's description in the passage now being considered of what happens when the prime conductor of an electrical machine draws its charge from the globe being rubbed proves beyond doubt that even in 1758 he was still expounding very orthodox views on the subject of atmospheres; the charge developed on the globe, he assured his readers, was constantly discharged into the chain (i.e. the prime conductor), ‘e così e in essa, e intorno ad essa si accumulerà un eccesso di vapore, il quale per la sua forza diffusiva si spanderà alquanto nell’ aria, ma dalla resistenza, e inazione di lei sarà intorno alla catena ritenuto, e quasi contro di essa ripercosso’.

⁶⁰ Beccaria, , op. cit. (57), pp. 42–3Google Scholar. The original Italian is: ‘Se il vapore diffondendosi da A, che ne ha più, in B, che ne ha meno, discaccia l'aria, ch'è tra A, e B, prevaierà l'aria, che al di fuori preme A, e B; onde A, e B urtati da quest' eccesso di pressione, si avvicineranno con moto eguale, e proporzionale alla quantità del vapore, che tra essi trascorrerà’. Beccaria at first presented his views somewhat hesitantly, but in a letter to Franklin soon afterwards he spoke with rather more confidence (Philosophical transactions, li [1759–1760], 514–26Google Scholar; English translation in Franklin, 's Papers, vii, 300–14Google Scholar). Beccaria's ideas have been described more fully in Gliozzi, Mario, ‘Beccaria nella storia dell' elettricità’, Archeion, xvii (1935), 15–47CrossRefGoogle Scholar; they bear a strong resemblance to those of the earlier electrical theorists, particularly Hauksbee (see, for example, my article ‘Francis Hauksbee's theory of electricity’, Archive for history of exact sciences, iii [1967], 203–17).Google Scholar

⁶¹ See above, note 52, for its impact on Franklin himself and on his disciple DeLor.

⁶² Boscovich, Roger, A theory of natural philosophy (Cambridge, Mass.: M.I.T. Press, 1966Google Scholar; English translation of the edition of 1763), p. 181.

⁶³ See, for example, von Haller, Albrecht, Mémoires sur la nature sensible et irritable, des parties du corps animal (Lausanne, 1756–1760), iii. 207Google Scholar. See also my paper ‘Electricity and the nervous fluid’, Journal of the history of biology, iii (1970), 235–51Google Scholar, for a discussion of this point.

⁶⁴ Elettricismo artificiale, cited in note 59. I have also used the English translation of this which appeared a few years later with the tide A treatise upon artificial electricity (London, 1776)Google Scholar. Beccaria had certainly read Aepinus by the time he committed his new views to print, since he cited the latter's Tentamen explicitly at one point (Elettricismo artificiale p. 175Google Scholar). See also note 65 below.

⁶⁵ Beccaria, , Treatise, p. 179Google Scholar. Significantly, it was precisely to support this assertion that Beccaria cited Aepinus.

⁶⁶ Ibid., pp. 1–2. Aepinus's statement of the distinction is to be found in his Tentamen, p. 10.

⁶⁷ The electrical researches of the Honourable Henry Cavendish, F.R.S., ed. Maxwell, James Clerk (Cambridge, 1879), p. 100Google Scholar. For the dating of Cavendish's draft see McCormmach, , op. cit. (32), pp. 146–7.Google Scholar

⁶⁸ Priestley, , op. cit. (46), p. 457Google Scholar. It should be noted that in the case of repulsions between bodies carrying like charges Priestley presented Franklin's own account, and not any of those put forward by his commentators, as the standard version.

⁶⁹ Ibid. (3rd edn., London, 1775), ii. 28. Priestley also left unaltered a most interesting comment on the famous ‘electrified cup’ experiment. In his usual eclectic fashion, besides drawing his well-known inference that the electrical force is inverse-square in character, he added: ‘Do not these experiments, likewise, favour the hypothesis of S. Beccaria, that there is no electrical attraction without a communication of electricity?’ (Ibid., ii. 374).