94 
History. to ignite three feet. It had not the power of decompo- 
sing barytes and other similar substances; it did not 
affect Bennet’s electrometer ; and it seemed scarcely able 
to produce a perceptible shock. 
Compara- 
tive effects 
of smaller 
plates, 
plates of two inches square, affording a surface ‘of 83200 
inches. With this the alkalies and alkaline earths were 
readily decomposed, and a considerable divergence was 
. produced in the gold leaves of the electrometer. From 
this comparison of the effects of the two batteries, we 
are led to the conclusion which has been already refer- 
red to, that the intensity of the electricity is increased 
with the number, and the quantity of it with the extent 
of the metallic plates. Upon this principle, we may 
explain why the platina wire was acted upon more rea- 
dily than the iron wire, the more perfect conducting 
‘quality of the former presenting no obstacle to the pas- 
sage of the electricity through it; while the tendency 
of the iron to oxidation required a greater intensity of 
the fluid to effect its transmission through the wire. In 
this paper, the author states, that he has removed one 
‘of the objections that have been urged against the 
identity of the galvanic and the common electricity, 
that the former has no striking distance ; by employing 
a proper apparatus, he ascertained that the galvanic 
spark was capable of passing through a certain space 
between the extremities of two platina wires. 
Mr Children’s general conclusion is, that ‘ the abso- 
lute effect of a voltaic apparatus is in the compound 
ratio of the number and size of the plates ; the intensi- 
ty of the electricity being as the former, the quantity 
given out as the latter ; consequently, regard must be 
had in its construction, to the purposes for which it is 
designed. For experiments on perfect conductors, very 
large plates are to be preferred, a small number of 
which will probably be sufficient; but where the re- 
sistence of imperfect conductors is to be overcome, the 
combination must be great, but the size of the plates 
must be small. But if quantity and intensity be both 
required, then a great number of large plates will be 
necessary. For general purposes, four inches square 
will be found to be the most convenient size.” See 
Phil. Trans. for 1809, p. 32. 
Striking 
distance of 
galvanic 
electricity. 
General 
conclusion. 
Sry oe Mr Children has since constructed a still larger and 
>. 181s. more powerful battery, consisting of 20 pairs of copper 
and zine plates, each plate being six feet by two feet 
eight inches. It ignited six feet of thick platina wire, 
and melted platina with great facility ; it also melted iri- 
dium and osmium. At the suggestion of Dr Wollaston, 
a singular fact was ascertained, that a greater length of 
thick platina wire was ignited, than of platina wire 
Parr II. 
Accorprxe to the plan which was laid down, we 
must now proceed to give an account of the theories 
and hypotheses that have been formed to explain the 
phenomena of galvanism. We have had occasion to al- 
ude to many of these in the course of our historical 
sketch; and the reader will, in some degree, have anti- 
cipated our opinion respecting them, The subject di- 
vides itself into several branches, partly corresponding 
with the progress of our knowledge of the facts that 
were gradually developed, and partly depending upon 
the supposed relation of galvanism to the other depart- 
ments of natural philosophy, 
#alvani’s In this concise view of the science, we shall not 
hypothesis. think it necessary to enter into the merits of the earlier 
Theory. 
General 
remarks, 
GALVANISM. 
Mr Children next formed a battery of 200 pairs of 
THEORY OF GALVANISM. 
of amuch smaller size. See Thomson’s Annals, ii, 147, 
- We have given some account of a paper of Erman’s, 
in which he endeavours to show, that certain bodies are 
what he calls Unipolar, that is, that they are conductors 
of one kind of electricity only. Mr Brande conceived, 
that the facts brought forward by Erman, might admit 
of a better explanation upon a different principle, viz. 
that some chemical bodies, being naturally positive, and 
others naturally negative, they would be attracted to 
the surface of the pile in a contrary state to their own, 
the positive to the negative, and the negative to the 
positive surface. 
In order to submit his opinion to the test of experi- 
ment, Mr Brande mE two insulated metallic balls, ments. 
one connected with the prime conductor, and the other 
with the rubber of an electrical machine; and placing 
between them the different substances under examina- - 
tion, he observed to which of the balls they were at- 
tracted. . He found that the flame “= a candle, which 
princi consists of carbon and hydrogen, was at- 
Peaet ibe negative ball; while the Toate of ph 
‘rus, which would contain a quantity of phosphoric acid, 
was attracted to the positive side ere the i 
seemed to follow the Dodi laws of electro-chemi 
attraction, according’ to the idea of their inherent elec- 
trical states; and the other experiments which he per- 
formed of a similar nature generally tended to the same 
conclusion. The facts stated in this paper are concei- 
ved to be favourable to the hypothesis of Sir H. Davy, . 
respecting the natural electricities of bodies, and also, 
when viewed in connexion with Erman’s observations, 
to afford an additional proof of the identity of electrici- 
ty and galvanism. See Phil. Trans. for 1814. ; 
Dr Wollaston has constructed an apparatus, which Wollast 
he calls an elementary galvanic battery, the object of element 
which is to exhibit the most minute arr ent. of ets 
electrical substances, by which visible ignition can be- 
produced. The smallest that he has constructed con- 
ist 
-sists of a thimble, without its top, flattened until its sides 
-were about one-fifth of an inch asunder ; a small plate ~ 
of zine was then contrived to be fixed within the thimble, 
but without touching it, and a proper appendage of 
platina wires was added. ‘The zinc plate was less than 
three-fourths of an inch square, and even when a yery 
diluted acid was employed, a platina wire of -.*,,, of an 
inch in diameter was readily fused. See Thomson’s 
Annals, vi. 309. 
These experiments of Dr Wollaston’s are the latest 
that have been made on the subject of galvanism, and 
will bring down the history of the science to the pre- 
sent period, ; 
speculations, that have heen superseded by later disco- 
veries. Of this nature is the original hypothesis of 
Galvani himself, that the convulsions which he obser- 
ved in the muscles of frogs, were produced by a new 
and peculiar agent, residing in the body, to which he 
gave the name of Animal Electricity. Although there 
are some few cases which seem to militate against the 
supposition, it must, Zig the whole, be regarded as 
being decisively proved, that all the phenomena which 
we stile galvanic, depend merely upon the action of 
electricity, modified by the manner in which it is pro- 
duced or excited. . 
Hence arises an interesting question, and one which 
lies at the very foundation of all our future inquiries, 
