Information Technology Reference
In-Depth Information
FIGURE 1.11
A semaphore telegraph tower on the first line from Paris to Lille (1794).
(Leemage/Getty Image)
For more than two thousand years amber's ability to attract other materials was seen
as a curiosity with no practical value, but in the seventeenth and eighteenth centuries
scientists began to study electricity in earnest. Alessandro Volta, a professor of physics at
the University of Pavia, made a key breakthrough when he discovered that electricity
could be generated chemically. He produced an electric current by submerging two
different metals close to each other in an acid. In 1799 Volta used this principle to create
the world's first battery. Volta's battery produced an electric charge more than 1,000
times as powerful as that produced by rubbing amber. Scientists soon put this power
to practical use.
In 1820 Danish physicist Christian Oersted discovered that an electric current cre-
ates a magnetic field. Five years later British electrician William Sturgeon constructed an
electromagnet by coiling wire around a horseshoe-shaped piece of iron. When he ran an
electric current through the coil, the iron became magnetized. Sturgeon showed how a
single battery was capable of producing a charge strong enough to pick up a nine-pound
metal object.
In 1830 American professor Joseph Henry rigged up an experiment that showed
how a telegraph machine could work. He strung a mile of wire around the walls of
his classroom at the Albany Academy. At one end he placed a battery; at the other
end he connected an electromagnet, a pivoting metal bar, and a bell. When Henry
connected the battery, the electromagnet attracted the metal bar, causing it to ring the
bell. Disconnecting the battery allowed the bar to return to its original position. In this
way he could produce a series of rings.
