964 
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,! 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, &e, 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 
August1796. Theform of the arrangement resembled 
that afterwards adopted in the Cowronne 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 
Repulsion negative, and so of other metals. Volta used for 
due to con- this experiment Nicholson’s ingenious modification of 
eaterd 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 element 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 zine 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 
Volta’s 
theory of 
electro- 
motion. 
Invention 
of the pile. 
MATHEMATICAL AND PHYSICAL SCIENCE. 
(Diss. VI. 
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 Fabbroni 
was entirely mechanical, and due to contact merely cme chanile 
—and whilst Galvani, his relative Aldini, and others, cal origin 
maintained strenuously the vital theory, in which they of galvan- 
were substantially confirmed by no less authorities 
than Wells and Baron von Humboldt—a third school 
appeared, at first little popular, represented by Fas- 
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,? 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.* 
We have seen that already in 1796 Volta had ar- 
rived at a knowledge of the principle that the electric ocription OF 
effect of the metals might be increased by combining pis pile, 
two sets of triple elements similarly disposed, which, and its ef 
unknown to him, Robison had already done (749). fect 
1 Volta, Opere, vol. ii, part 2. 2 In quarto, vol. iv. (1800). 
3 See an account of him in the third volume of Cuvier’s Eloges. 
