CX
or due to a quiet exchange of electricities through points, see
§ 274. Aurora borealis was called by A. V. Humboldt a
“magnetic thunderstorm”, because it is his opinion, that this
phenomenon is caused by a restitution of the earth's magnetism
after it has been disturbed (for another hypothesis see Q. 437.)
§ 277. 5) Galvanic electricity (electricity due to chemical
action). Professor Galvani discovered this second source of
electricity quite accidentally (1789). A dead frog was suspend
ed by a hook of copper to the iron railing of a balcony. As
often as the animal’s legs came in contact with the iron bars the
frog was violently contracted. At first this electricity was as
sumed to be an electricity inherent in the animal (sce § 302)
and was called vital fluid, but Professor Volta turned his atten
tion from the frog to the connecting metals and assumed, that
the disengagement must be due to the contact of the two metals.
A controversy between the two professors led to the propound
ing of the following principle: When two heterogeneous sub
stances are placed in contact, one of them always assumes the
positive and the other the negative electrical condition.
This may be proved by putting one's tongue between a stripe
of copper and one of zinc and placing both stripes in contact
outside the mouth. 438.
§ 278. One and the same metal connected with two other
different metals may assume positive or negative electricity.
We may arrange the metals in such a manner, that any one of
them is electrified with the preceding negatively and with the
succeeding positively, f.e. zinc, lead, tin, iron, copper, silver,
gold, platinum, coal—.
The more two of the metals in this series are distant from
each other the stronger the tension of the electricity produced
by them will be (electromotive force); their force will be equal
