The Story of Electricity | Page 2

LIGHT AND
HEAT VIII. ELECTRIC POWER IX. MINOR USES OF

ELECTRICITY X. THE WIRELESS TELEGRAPH XI.
ELECTRO-CHEMISTRY AND ELECTRO-METALLURGY XII.
ELECTRIC RAILWAYS APPENDIX

THE STORY OF ELECTRICITY.

CHAPTER I
.
THE ELECTRICITY OF FRICTION.
A schoolboy who rubs a stick of sealing-wax on the sleeve of his jacket,
then holds it over dusty shreds or bits of straw to see them fly up and
cling to the wax, repeats without knowing it the fundamental
experiment of electricity. In rubbing the wax on his coat he has
electrified it, and the dry dust or bits of wool are attracted to it by
reason of a mysterious process which is called "induction."
Electricity, like fire, was probably discovered by some primeval savage.
According to Humboldt, the Indians of the Orinoco sometimes amuse
themselves by rubbing certain beans to make them attract wisps of the
wild cotton, and the custom is doubtless very old. Certainly the ancient
Greeks knew that a piece of amber had when rubbed the property of
attracting light bodies. Thales of Miletus, wisest of the Seven Sages,
and father of Greek philosophy, explained this curious effect by the
presence of a "soul" in the amber, whatever he meant by that. Thales
flourished 600 years before the Christian era, while Croesus reigned in
Lydia, and Cyrus the Great, in Persia, when the renowned Solon gave
his laws to Athens, and Necos, King of Egypt, made war on Josiah,
King of Judah, and after defeating him at Megiddo, dedicated the
corslet he had worn during the battle to Apollo Didymaeus in the
temple of Branchidas, near Miletus.
Amber, the fossil resin of a pine tree, was found in Sicily, the shores of
the Baltic, and other parts of Europe. It was a precious stone then as
now, and an article of trade with the Phoenicians, those early merchants
of the Mediterranean. The attractive power might enhance the value of
the gem in the eyes of the superstitious ancients, but they do not seem
to have investigated it, and beyond the speculation of Thales, they have
told us nothing more about it.

Towards the end of the sixteenth century Dr. Gilbert of Colchester,
physician to Queen Elizabeth, made this property the subject of
experiment, and showed that, far from being peculiar to amber, it was
possessed by sulphur, wax, glass, and many other bodies which he
called electrics, from the Greek word elektron, signifying amber. This
great discovery was the starting-point of the modern science of
electricity. That feeble and mysterious force which had been the
wonder of the simple and the amusement of the vain could not be
slighted any longer as a curious freak of nature, but assuredly none
dreamt that a day was dawning in which it would transform the world.
Otto von Guericke, burgomaster of Magdeburg, was the first to invent a
machine for exciting the electric power in larger quantities by simply
turning a ball of sulphur between the bare hands. Improved by Sir Isaac
Newton and others, who employed glass rubbed with silk, it created
sparks several inches long. The ordinary frictional machine as now
made is illustrated in figure i, where P is a disc of plate glass mounted
on a spindle and turned by hand. Rubbers of silk R, smeared with an
amalgam of mercury and tin, to increase their efficiency, press the rim
of the plate between them as it revolves, and a brass conductor C,
insulated on glass posts, is fitted with points like the teeth of a comb,
which, as the electrified surface of the plate passes by, collect the
electricity and charge the conductor with positive electricity. Machines
of this sort have been made with plates 7 feet in diameter, and yielding
sparks nearly 2 feet long.
The properties of the "electric fire," as it was now called, were chiefly
investigated by Dufay. To refine on the primitive experiment let us
replace the shreds by a pithball hung from a support by a silk thread, as
in figure 2. If we rub the glass rod vigorously with a silk handkerchief
and hold it near, the ball will fly toward the rod. Similarly we may rub
a stick of sealing wax, a bar of sulphur, indeed, a great variety of
substances, and by this easy test we shall find them electrified. Glass
rubbed with glass will not show any sign of electrification, nor will
wax rubbed on wax; but when the rubber is of a different material to
the thing rubbed, we shall find, on using proper precautions, that
electricity is developed. In fact, the property which was once thought
peculiar to amber is found to belong to all bodies. ANY SUBSTANCE,
WHEN RUBBED WITH A DIFFERENT SUBSTANCE, BECOMES

ELECTRIFIED.
The electricity thus produced is termed frictional electricity. Of course
there are