SOME of the phenomena of electricity are manifested upon so large a
scale as to be thrust upon the attention of everybody. Thus lightning,
which accompanies so many showers in warm weather in almost every
latitude, has always excited in some individuals a superstitious awe, as
being an exhibition of supernatural agency; and probably every one feels
more or less dread of it during a thunder-shower, and this for the
reason that it affects so many of the senses at the same time. The flash
may be blinding to the eyes if near to us; the thunder may be deafening
to the ears, and so powerful as to shake the foundations of the hills,
and make the ground upon which we stand to sensibly move: these with the
remembered destructive effects that have been witnessed, of buildings
demolished and large trees torn to splinters in an instant, are quite
sufficient to raise a feeling of dread in the strongest mind. In the
polar regions, both north and south, where thunder-storms are less
frequent, the atmospheric electricity assumes the form called the aurora
borealis, or the aurora australis, according as it is seen north or
south of the equator.
More than two thousand years ago it was noticed by the Greeks that a
certain kind of a mineral which was thrown up on the shores of the
Mediterranean Sea, when rubbed would attract light bodies, such as
shreds of silk or linen and bits of paper. To this substance they gave
the name of Elektron, and the property developed thus by friction was
afterwards called electricity. In 1600 Dr. Gilbert, physician to Queen
Elizabeth, published a book in which he described numerous experiments
demonstrating that electricity could be developed by friction upon a
great variety of substances, such as stones, gems, and resins. The first
machine for developing electricity was made by Otto von Guericke of
Magdeburg, about 1680. His machine consisted of a ball of sulphur about
six inches in diameter, which could be rotated. If the dry hand were
held against the sulphur while it was being turned in a dark room, the
sphere appeared to emit light: it also gave out a peculiar hissing or
crackling sound. Newton experimented a little with electricity, and
noticed that the rubber was an important element in developing
electricity. He does not seem to have given to the subject the same
attention that he gave to some other departments of science. Had he done
so, it is probable that he would have advanced the study a hundred
years; that is to say, he would probably have left it at the place where
it actually was in 1790. So great were his abilities that in one
lifetime he made greater additions to human knowledge than all the rest
of mankind had made during the preceding thousand years. In the month of
June, 1752, Franklin made that memorable experiment which immortalized
him. He flew his kite to the thunder-cloud, practically asking the
question of the lightning whether or not it was identical with
electricity. The lightning came down the wetted twine to his hand, and
proclaimed its identity.
For the next forty years the natural philosophers in both Europe and
America only rung the changes upon what was known. They flew kites to
the clouds; they made and charged Leyden jars, and discharged them
through wires and chains and circuits of clasped hands, and studied the
attractions and repulsions manifested by electrified bodies; but they
added nothing of importance in the way of experiments.
In 1791 Galvani, a professor of anatomy at Bologna, announced a
manifestation of electricity that was new and of a remarkable character,
having its origin in the muscles of animals, and so was called animal
electricity. He had some frogs' legs prepared for eating; by chance they
were placed near an electrical machine with which Galvani was
experimenting, so that a spark would occasionally pass to the legs, when
they would contract as often as a spark passed to them. The motion was
first observed by his wife, who called his attention to the phenomenon;
and he very soon discovered that the thighs of a frog, skinned and
suspended, made a very good electroscope. While experimenting in this
way he made another and more important discovery; namely, that, when
the muscles and nerves of the frog's leg were touched by pieces of two
different metals, the leg would contract as before. Alexander Volta,
another Italian professor, who had invented the electrophorus, and was
possessed of great experimental skill, now turned his attention to the
experiment of Galvani, and very soon discovered that the origin of the
electricity that moved the frogs' legs was not in the legs themselves,
but in the metals used. The first form of the galvanic battery was the
result of Volta's investigations, and was called the Voltaic pile. This
pile consisted of alternate disks of zinc, flannel, and copper, piled
one on top of the other in constant succession in that order. The
flannel was moistened with salt and water, or with diluted sulphuric
acid. When the first zinc was connected with the last copper by means of
a wire, a powerful current of electricity was obtained. This form of
battery is not in use at all now, as much more efficient means are known
for producing electricity; but this in 1800, when it was first made
known in England, was very startling, and was one of those surprises
which have been so frequent since then in the history of electricity.
Surprising things were done by Sir Humphry Davy, with a large Voltaic
battery. Water was decomposed, and the metals potassium and sodium were
first separated from their compounds with oxygen. Bonaparte had offered
a prize of sixty thousand francs "to the person who by his experiments
and discoveries should advance the knowledge of electricity and
galvanism as much as Franklin and Volta did," and of "three thousand
francs for the best experiments which should be made in each year on the
galvanic fluid." This latter prize was awarded to Davy.
After Davy's successes in 1806, there was nothing of importance in an
experimental way added to the knowledge of electricity, until 1820, when
Oersted of Copenhagen announced that "the conducting wire of a Voltaic
circuit acts upon a magnetic needle," and that the needle tends to set
itself at right angles to the wire. This was a kind of action altogether
unexpected. This observation was of the utmost importance; and at once
the philosophers in Europe and America set themselves to inquire into
the new phenomenon. The laws of the motion of the magnetic needle when
acted upon by a current of electricity traversing a wire were
successfully investigated by M. Ampere of the French Academy. He
observed that whenever a wire through which a current of electricity was
passing was held over and parallel with a magnetic needle which was free
to move, and therefore pointed to the north, if the current was moving
_towards_ the north, the north pole was deflected to the west; if the
current was moving towards the south, the south pole of the magnet was
deflected towards the west; and that in all cases the magnet tended to
set itself at right angles to the current; also that this angular
displacement depended upon the strength of the current. Thus originated
the _galvanometer_, an instrument that not only detects the existence of
an electric current, but enables us to determine its direction and its
strength. Our present knowledge of electrical laws is due, in a very
large measure, to observations made with this instrument. Of course it
has been very much modified, and made almost incredibly sensitive: yet,
in all galvanometers, the fundamental principle involved in their
structure is that of the action of a current of electricity upon a
magnet, which was first noticed by Oersted.