166 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



Volta's 

 theory of 

 electro- 

 motion. 



Invention 

 of the pile 



Repulsion 

 due to con' 

 tact of 

 metals. 



we find Volta gradually insisting more on the purely 

 mechanical nature of the electrical excitement. The 

 last-named year produced an important letter to 

 Gren of Halle, 1 which contains the real germ of the 

 invention of the pile, though it has been little taken 

 notice of. We there find conducting bodies divided 

 into two classes, primary and secondary ; the first 

 including metals, metallic ores, and charcoal ; the se- 

 cond liquids, solutions, animal tissues, &c. The first 

 class he also called motors. Using the prepared 

 frog always as an indicator, he tried the effect of 

 combining three or more elements of the two kinds. 

 He found that a double combination of three ele- 

 ments, when arranged so that their order was re- 

 versed, neutralized each other, or produced no 

 spasm ; on the contrary, when the two combinations 

 conspired in direction, the convulsions were in- 

 creased ( xii., xv., xix.). This appears to define the 

 date of Volta's discovery of the principle of the pile 

 that, namely, of superadding minute effects to be 

 August 1796. The form of the arrangement resembled 

 that afterwards adopted in the Couronne des Tasses. 

 The second letter to Gren, dated the same month of 

 August 1796, contains the important discovery (the 

 most important abstractly of any due to Volta), that 

 the electricity set in motion by the contact of unlike 

 metals may, by means of the condenser (due also to 

 him), be made evident by the usual effect of repul- 

 sion on the common electrometer : thus when zinc 

 and silver are used, the former is positive, the latter 

 negative, and so of other metals. Volta used for 

 this experiment Nicholson's ingenious modification of 

 his own condenser, called a Revolving Doubler. It 

 must be owned that the experiment, in its simplest 

 form, is difficult of repetition, and that Nicholson's 

 instrument sometimes gives delusive results. But 

 Volta's great address in practical electricity, and his 

 fairness in stating his results, leave no doubt of the 

 reality of his discovery, which evidently for the first 

 time eliminated the physiological clement of Gal- 

 vani's experiments, leaving the recognised mechanical 

 effects of electricity due to the contact of unlike 

 metals ; and, therefore, deserved the highest honour 

 which could be bestowed. Pfaff had already con- 

 structed a table of the electro-motive power of metals 

 by their actions on the frog, in which zinc stood at 

 one end, carbon at the other. But one of the most 

 curious parts of the paper by Volta is the evidence of 

 a strong suspicion which had crossed his mind, and 

 been for a time entertained, that in his experiments 

 with combinations of three elements two metallic, 

 and one humid the electricity was developed sepa- 

 rately at the contacts of the latter with the two for- 

 mer, and that the resulting current was merely the 

 difference of the two in favour of the stronger. Truly 

 in this whole history we may see how often first sug- 

 gestions have a peculiar and intuitive worth, which 



reflection and controversy often only obscure ! This 

 is, of course, the case rather in the research of causes 

 than of the means of rendering discovery practical. 



Whilst Volta was thus maintaining the opinion (751). 

 that the electricity excited by the contact of metals F abbron i 

 was entirely mechanical, and due to contact merely ; t^ef hemi 

 and whilst Galvani, his relative Aldini, and others, cal origin 

 maintained strenuously the vital theory, in which they ? f galvan. 

 were substantially confirmed by no less authorities iam ' 

 than Wells and Baron von Humboldt a third school 

 appeared, at first little popular, represented by FAB- 

 BRONI, a Tuscan chemist and natural philosopher of 

 no small merit. His papers published, I believe, 

 in 1799, though written several years previously, and 

 some as far back as 1792, of which a full abstract is 

 given in Nicolson's Journal, 2 show great acuteness. 

 He attributed the effects of the contact of metals to 

 a chemical action developed at the place of contact. 

 He referred to Sulzer's experiment of the taste of 

 heterogeneous metals applied to the tongue and to 

 many instances of the rapid oxidation of heterogeneous 

 metals in contact, when exposed to heat and mois- 

 ture. Amongst others, by a remarkable anticipation 

 of one of the most curious applications of the elec- 

 tro-chemical theory, he notices the oxidation of the 

 copper sheathing of ships. Without " excluding all 

 electrical influence from the prodigious effects of gal- 

 vanism," he infers that there are chemical forces 

 " exerted with the swiftness of lightning," to which 

 the physiological effects, and perhaps some others 

 ascribed to electricity, are probably due. Thus, he 

 says, " the experiment of Sulzer is nothing more 

 than a combustion or chemical operation, as is proved 

 not only by its result but by its duration ; for elec- 

 tricity acts always instantaneously, whereas the ef- 

 fect of chemical affinities continues so long as the 

 re-agents are not saturated." The weak point of 

 Volta's theory of electro-motion is here cleverly hit. 

 That effects indefinitely prolonged, capable of pro- 

 ducing mechanical, chemical, and vital changes, 

 without any mutual action between the touching 

 bodies, save mere pressure, appears indeed a paradox 

 startling even to a first inventor, but which, when 

 maintained by successive generations of able men, 

 may rank as a delusion more memorable than the 

 phlogistic theory of the older chemists. Fabbroni 

 did not himself pursue his ingenious speculations, 

 but his papers, though now almost forgotten, acted 

 powerfully on the minds of his contemporaries, as 

 we shall see in the next section. He died at the age 

 of 70, in 1822, having spent most of his life in pa- 

 triotic and useful labours in his native country. 3 



We have seen that already in 1796 Volta had ar- 

 rived at a knowledge of the principle that the electric ri 

 effect of the metals might be increased by combining ^ s 

 two sets of triple elements similarly disposed, which, and its ef- 

 unknown to him, Robison had already done (749). fects - 



(752.) 





1 Volta, Opere, vol. ii., part 2. 2 In quarto, vol. iv. (1800). s See an account of him in the third volume of Cuvier's Eloyes. 



