The Science Book

EXPANDING HORIZONS 93

resin disk rubbed with cat fur
to give it a static electric charge.
Each time a metal disk was placed
over the resin, the charge was
transferred, electrifying the
metal disk.
Volta stated that Galvani’s
animal electricity was “among
the demonstrated truths.” But he
soon began to have his doubts.
He came to the conclusion that
the electricity causing the frog’s
legs to twitch on the hook came
from the touching of the two
different metals (the brass and the
iron). He published his ideas in
1792 and 1793, and began
investigating the phenomenon.
Volta found that a single
junction of two different metals
did not produce much electricity,
although there was enough for him
to feel a curious sensation with
his tongue. But then he had the
brilliant idea of multiplying the
effect by making a series of such
junctions connected by salt water.
He took a small disk of copper, then
placed a disk of zinc on top, then a
piece of cardboard soaked in salt
water, then another disk of copper,
zinc, salty wet cardboard, copper,

zinc, and so on, until he had a

column, or stack. In other words,

he created a pile, or “battery.” The

point of the salty wet cardboard

was to carry the electricity without

letting the metals on either side of

it come into contact with each other.

The result was, literally,

electrifying. Volta’s crude battery

probably produced only a few volts

(the electrical unit named after

him), but that was enough to make

a tiny spark when the two ends

See also: Henry Cavendish 78–79 ■ Benjamin Franklin 81 ■ Joseph Priestley 82–83 ■ Humphry Davy 114 ■
Hans Christian Ørsted 120 ■ Michael Faraday 121

Each metal has a certain

power, which is different from

metal to metal, of setting the

electric fluid in motion.

Alessandro Volta

This diagram of a voltaic

pile shows the copper and

zinc disks separated by

cardboard soaked in salt

water. Volta’s original piles

contained an additional

zinc disk at the bottom,

and an additional copper

disk at the top. These

were later shown to be

unnecessary to produce

the electrical current.

Individual

element

Copper

disk

Zinc disk

Cardboard disk

were connected by a piece of wire,

and enough to give him a mild

electric shock.

The news spreads

Volta made his discovery in

1799, and news spread rapidly.

He demonstrated the effect to

Napoleon Bonaparte in 1801, but

more importantly, in March 1800,

he had reported his results in a

long letter to Sir Joseph Banks,

president of the Royal Society in ❯❯