It was with great satisfaction and much pleasure that I studied the last instalment of your excellent journal. I must begin by expressing my deepest respect and admiration for those men of science who contributed to it and who in doing so continue to enrich man’s understanding of the physical nature of our world, but especially for the excellent Alessandro Volta whose revolutionary work will no doubt prove to be influential for centuries to come. As a result it is with great caution and unease that I pen this letter yet I do so because I absolutely believe that what I am about to propose will be of great value in the debate regarding the nature of electricity.
I wish to discuss with you and indeed, with your esteemed readers, the work of the honourable Mr Volta and more specifically his ideas concerning animal electricity and its relation to the much discussed ‘pile’ or Metallic Electricity. I will begin, if you will permit me, by illustrating his approach to animal electricity and will proceed to describe what appears to me as a genuinely incoherent and contradictory line of argument. I thoroughly expect your readers to question exactly how the seemingly abandoned concept of animal electricity is relevant to this current topic; however I intend to argue that it is not only relevant but indeed essential, in highlighting a bizarre yet fundamental flaw in Mr Volta’s Metallic Electricity.
For the benefit of the reader I will begin with the story of Galvani whose accidental discovery of the sudden convulsion of a pair of frogs legs combined with his excellent experimental ability led him to refute the concept of atmospheric electricity and instead propose electricity is indeed inherent within the nerve pathways of living beings. Galvani describes his discovery in part three of his Commentary on the effect of electricity on muscular motion.
‘I was on the point of postulating that such contractions result from atmospheric electricity slowly insinuating itself in the animal, accumulating there, and then being rapidly discharged when the hook comes in contact with the iron railing. But when I brought the animal into a closed room, placed it on an iron plate, and began to press the hook which was fastened in the spinal cord against the plate, behold!, the same contractions and movements occurred as before. I immediately repeated the experiment in different places with different metals and at different hours of the day. The results were the same except that the contractions varied with the metals used. These results surprised us greatly and led us to suspect that the electricity was inherent in the animal itself.’1
As any true gentleman of science would be Mr Volta was fascinated by such a discovery and despite initially accepting the conclusion, became increasingly perplexed by Galvani’s comments about the effect of the various metals that made up the external arc in altering the strength of the convulsions. As far as I am aware Galvani dismissed this fact as unimportant. Credit should certainly be given to Mr Volta for seizing on this point as it has since proved to be one of great importance.
I was privileged enough to be in the audience on the 5 May 1792 when Mr Volta first hinted at the concept of metallic electricity. A subsequent letter was read out in December 1793 at the Royal Society that states:
‘The name animal electricity is by no means proper in the sense intended by Galvani and others, namely, that the electric fluid becomes unbalanced in the animal organ,...by some particular action of the vital powers. No this is mere artificial electricity induced by an external cause, that is, excited originally in a manner hithero unknown by the connexion of metals with any kind of wet substance’2
Following these comments Mr Volta went on to unveil his electric pile through the illuminating work which we were treated to in the last edition of your journal. It seems to me however, to be astonishingly brave and perhaps foolish to rule out altogether the idea of animal electricity as Mr Volta chooses to do in the above passage, given that he must be fully aware of the excellent papers printed in the Philosophical Transactions in 1782 by both John Hunter and John Walsh. Mr Walsh’s letter to Benjamin Franklin entitled ‘Of the electric property of the torpedo’ states, ‘It is with particular satisfaction that I make to you my first communication that the effect of the Torpedo appears to be absolutely electrical by forming its circuits through the same conductors as with electricity for instance metals and water and being intercepted by the same non conductors for instance glass and sealing wax.’ Mr Volta seemed up until now to ignore this obvious evidence in favour of animal electricity. It is not just the work of Mr Walsh and Mr Hunter that he disregards but also that of Alexander von Humboldt who has published an excellent work Versuche über die gereizte Muskel- und Nervenfaser in which he takes great care to show through detailed experimental technique that it is possible to produce contractions in the nerve-muscle region without the presence of a metal arc, seemingly refuting Mr Volta’s Metallic electricity.
‘When one cuts into a very much alive frog the portion x of the crucial nerve when one brings together almost immediately, with the aid of a glass tube, this portion of the nerve, the nerve itself and the muscle to which it is distributed, as soon as there will be some contraction in the leg Here there are absolutely only two heterogeneous substances, the nerve and the muscle’3
Mr Humboldt has without any doubt in my mind proved there is some form of electricity present within living organisms that can be ignited without the presence of Mr Volta’s metallic pile.
We are now getting to the crux of the matter. Mr Volta has offered no reply to Mr Humboldt other than to affirm his original position on the subject, something which continues to perplex me. However my confusion does not end there, I was utterly astonished to read in your very journal of Mr Volta’s latest claims in relation to animal electricity and specifically the electric Torpedo. He began in his paper dated 1800 by describing the arrangement of his pile, something which I must admit I am most grateful for and have myself received much enjoyment from experimenting with. He continued however, to insinuate that his electric pile provides a realistic model for the inner structure of the electric Torpedo.
‘To this apparatus, much more similar at bottom as I shall show, and even such as I have constructed it, in its form to the natural electric organ of the torpedo or electric eel than to the leyden flask.. is it not composed of entirely conducting bodies? Is it not active without any previous charge, without the aid of any electricity excited by any of the means hithero unknown? Does it not act incessantly and without intermission? And in the last place is it not capable of giving every moment shocks of greater of less strength’4
Not only has Mr Volta now travelled, it would appear, full circle in conceding there is a form of electricity present in living things, but his attempt to model this electricity on the Voltaic Pile seems to me to be utterly bizarre. Has he not had the good fortune to examine internally the electric eel or indeed to read Mr John Hunter’s excellent biological description? I myself have had the chance to do both and can confidently and overwhelmingly affirm there is no single fragment of metal and certainly no metallic pile to be found inside the electric organ of the torpedo.
In my humble opinion the Metallic pile is in no way an accurate representation of the electric organ of the torpedo; the organ does consist of a series of disk like membranes surrounded by fresh juice which does bear a similarity to the metallic pile, however, this is merely an aesthetic matter. The Torpedo fish contains no trace of metal and therefore we cannot use Mr Volta’s pile to explain its now widely acknowledged electric nature . We have long since accepted the theory of static electricity and remain happy to pursue our current investigation alongside this theory. I propose that Mr Volta was correct in identifying Metallic electricity and that it exists alongside static electricity, animal electricity and many other forms of the phenomena that we have yet to discover.
What could Mr Volta possibly be thinking in making such a statement? Have I in my ignorance missed something more profound? It seems to me given such substantial anatomical observations that in acknowledging that there is in fact, a form of electricity inherent within the animal, Mr Volta’s refutes his own Metallic electricity. I was discussing this predicament with a friend of mine Mr Pancaldi who himself had worked for a time with Mr Volta, he was able to provide me with a vital insight into the ingenuous mind of Mr Volta, an insight for which I am most grateful and am delighted to be able to share with you in this letteri.
Mr Pancaldi has suggested to me that Mr Volta’s over emphasis on metallic easily confuses the matter. In his opinion, an opinion I should say that I deeply respect, Mr Volta actually proposes that all conductors have the power to produce electricity when in contact with an alternative conductor. The phenomenon is not reserved to metals but extends to humid materials and liquids. Different materials however produce electricity with varying degrees of success, leading Mr Volta to produce his most interesting table that rates the apparent conducting strength of different materials. It seems Mr Volta focuses his discussion on metal as these are the most effective producers of electricity but his theory is by no means limited to them. Mr Pancaldi distinctly remembers him attempting to make a battery that might better represent the electric activity in the Torpedo consisting of eight pairs of disks of bone soaked with fresh water, Sulphuric acid and Potash and succeeding to produce a very small amount of electricity, 2.5 degrees to be exact. Whilst I would not like too much to speculate on Mr Volta’s reasoning I would question perhaps whether he is in fact attempting to assert that the entire structure of the electric torpedo consists of a series of humid and liquid conductors arranged in the most effective manner so as to produce the maximum amount of electricity.
Whilst this revelation does illuminate our understanding of Mr Volta’s approach to the problem of animal electricity it by no means solves the problem. Mr Volta is still wrong to claim his metallic pile is a suitable model of the electric eel. His failure to create a non-metallic pile that produces anything other than a minute amount of electric demonstrates the electric nature of the torpedo is still an unsolved mystery and certainly cannot be explained by Mr Volta’s contact theory.
As for the origin of electricity produced by the means of the contact of two conductors, it seems to be the case that Mr Volta has, perhaps deliberately, made little effort to propose an adequate theory that might begin to explain the phenomenon produced by the electric pile. Mr Volta is most likely well aware that instruments tend to be far less controversial than the theories explaining them. It is my understanding, again resulting from most constructive conversations with Mr Pancaldi that the most promising such explanation proposed by Mr Volta involves an analogy with heat. At a particular temperature different bodies have different capacities for retaining electricity, in the same way different bodies retain different amounts of Caloric at a given temperature. As long as a body retains the amount of electric fluid most suitable to it with respect to the given temperature and most significantly all primary (metallic) and secondary (humid) conductors with which it is in contact, it will remain in equilibrium and produce no electrical effects. A plate of Copper and another of Zinc on my table are in electric equilibrium as they retain the correct amount of electric fluid according to their relative capacities. If however I bring these metals into contact they now have a different electric capacity with respect to each other, as a result electricity flows between the plates to restore the equilibrium. Whilst the plates now contain the most suitable amount of electric fluid with respect to each other they have fallen out of equilibrium with the surrounding air and humid conductors with which they are in contact, again causing electricity to flow which as a result breaks the electric equilibrium with respect to the contact between the metals. This produces a continuous never ending flow of electricity, a flow that is most obviously observed between metals but no doubt takes place be it on a very small scale between all conducting materials.
I wish to end with this point, leaving it firmly in the mind of the readers, I would be most interested to learn what you and our fellow gentlemen of science have to say on the matter. I look forward to your response.
I have the honour to be, Sir,
Your constant reader
i For all discussion referring to ‘Mr Pancaldi’ see Giuliano Pancaldi 2005,Volta: Science and Culture in the Age of Enlightenment, Princeton University Press