||When the discoveries
of Faraday of electro-magnetic induction had made possible the means of
easily generating electricity, the next natural step was to find a means
of storing it or accumulating it. This, however, proved no easy matter,
and as yet a practical storage or secondary battery that is neither too
cumbersome, too fragile, nor too weak in its action has not been invented.
If a satisfactory storage battery could be made, it is obvious that its
revolutionary effects could scarcely be overestimated. In the single field
of aeronautics, it would probably solve the question of aerial navigation.
Little wonder, then, that inventors have sought so eagerly for the invention
of satisfactory storage batteries. As early as 1803 Ritter had attempted
to make such a secondary battery. In 1843 Grove also attempted it. But
it was not until 1859, when Gaston Planche produced his invention, that
anything like a reasonably satisfactory storage battery was made. Planche
discovered that sheets of lead immersed in dilute sulphuric acid were very
satisfactory for the production of polarization effects. He constructed
a battery of sheets of lead immersed in sulphuric acid, and, after charging
these for several hours from the cells of an ordinary Bunsen battery, was
able to get currents of great strength and considerable duration. This
battery, however, from its construction of lead, was necessarily heavy
and cumbersome. Faure improved it somewhat by coating the lead plates with
red-lead, thus increasing the capacity of the cell. Faure's invention gave
a fresh impetus to inventors, and shortly after the market was filled with
storage batteries of various kinds, most of them modifications of Planche's
or Faure's. The ardor of enthusiastic inventors soon flagged, however,
for all these storage batteries proved of little practical account in the
end, as compared with other known methods of generating power.
Three methods of generating electricity
are in general use: static or frictional electricity is generated by "plate"
or "static" machines; galvanic, generated by batteries based on Volta's
discovery; and induced, or faradic, generated either by chemical or mechanical
action. There is still another kind, thermo-electricity, that may be generated
in a most simple manner. In 1821 Seebecle, of Berlin, discovered that when
a circuit was formed of two wires of different metals, if there be a difference
in temperature at the juncture of these two metals an electrical current
will be established. In this way heat may be transmitted directly into
the energy of the current without the interposition of the steam-engine.
Batteries constructed in this way are of low resistance, however, although
by arranging several of them in "series," currents of considerable strength
can be generated. As yet, however, they are of little practical importance.
About the middle of the century Clerk-Maxwell
advanced the idea that light waves were really electro- magnetic waves.
If this were true and light proved to be simply one form of electrical
energy, then the same would be true of radiant heat. Maxwell advanced this
theory, but failed to substantiate it by experimental confirmation. But
Dr. Heinrich Hertz, a few years later, by a series of experiments, demonstrated
the correctness of Maxwell's surmises. What are now called "Hertzian waves"
are waves apparently identical with light waves, but of much lower pitch
or period. In his experiments Hertz showed that, under proper conditions,
electric sparks between polished balls were attended by ether waves of
the same nature as those of light, but of a pitch of several millions of
vibrations per second. These waves could be dealt with as if they were
light waves - reflected, refracted, and polarized. These are the waves
that are utilized in wireless telegraphy.