In 1830 the great American scientist Professor Joseph Henry transmitted the
first practical electrical signal. A short time before Henry had invented
the first efficient electromagnet. He also concluded similar thoughts about
induction before Faraday but he didn’t publish them first. Henry’s place in
electrical history however, has always been secure, in particular for
showing that electromagnetism could do more than create current or pick up
heavy weights — it could communicate.
In a stunning demonstration in his Albany Academy classroom, Henry created
the forerunner of the telegraph. IIn the demonstration, Henry first built an
electromagnet by winding an iron bar with several feet of wire. A pivot
mounted steel bar sat next to the magnet. A bell, in turn, stood next to
the bar. From the electromagnet Henry strung a mile of wire around the
inside of the classroom. He completed the circuit by connecting the ends of
the wires at a battery. Guess what happened? The steel bar swung toward the
magnet, of course, striking the bell at the same time. Breaking tthe
connection released the bar and it was free to strike again. And while
Henry did not pursue electrical signaling, he did help someone who did. And
that man was Samuel Finley Breese Morse.
For more information on Joseph Henry, visit the Joseph Henry PPapers Project
http://www.si.edu/archives/ihd/jhp/papers00.htm (external link)
From the December, 1963 American Heritage magazine, „a sketch of Henry’s
primitive telegraph, a dozen years before Morse, reveals the essential
components: an electromagnet activated by a distant battery, and a pivoted
iron bar that moves to ring a bell.“ See the two books listed to the left
for more information.
In 1837 Samuel Morse invented the first workable telegraph, applied for its
patent in 1838, an
d was finally granted it in 1848. Joseph Henry helped Morse build a
telegraph relay or repeater that allowed long distance operation. The
telegraph later helped unite the country and eventually the world. Not a
professional inventor, Morse was nevertheless captivated by electrical
experiments. In 1832 he heard of Faraday’s recently published work on
inductance, and was given an electromagnet at the ssame time to ponder over.
An idea came to him and Morse quickly worked out details for his telegraph.
As depicted below, his system used a key (a switch) to make or break the
electrical circuit, a battery to produce power, a single line joining one
telegraph station to another and an electromagnetic receiver or sounder
that upon being turned on and off, produced a clicking noise. He completed
the package by devising the Morse code system of dots and dashes. A quick
key tap broke the ccircuit momentarily, transmitting a short pulse to a
distant sounder, interpreted by an operator as a dot. A more lengthy break
produced a dash.
Telegraphy became big business
as it replaced messengers, the Pony Express, clipper ships and every other
slow paced means of communicating. The fact that service was limited to
Western Union offices or large firms seemed hardly a problem. After all,
communicating over long distances instantly was otherwise impossible. Yet
as the telegraph was perfected, man’s thoughts turned to speech over a
Bell continued harmonic telegraph work through the fall of 1874. He wasn’t
making much progress but his tinkering gathered attention. Gardiner Greene
Hubbard, a prominent Boston lawyer and the president of the Clarke School
for The Deaf, became interested in Bell’s experiments. He and George
Sanders, a prosperous Salem businessman, both sensed Bell might make the
harmonic telegraph work. They also knew Bell the man, since Bell tutored
Hubbard’s daughter and he was helping Sander’s deaf five year old son learn
In October, 1874, Green went to Washington D.C. to conduct a patent search.
Finding no invention similar to Bell’s proposed harmonic telegraph, Hubbard
and Sanders began funding Bell. All three later signed a formal agreement
in February, 1875, giving Bell financial backing in return for equal shares
from any patents Bell developed. TThe trio got along but they would have
their problems. Sanders would court bankruptcy by investing over $100,000
before any return came to him. Hubbard, on the other hand, discouraged
Bell’s romance with his daughter until the harmonic telegraph was invented.
Bell, in turn, would risk his funding by working so hard on the telephone
and by getting engaged to Mabel without Hubbard’s permission.
In the spring of 1875, Bell’s experimenting picked up quickly with the help
of a talented young machinist named Thomas A. Watson. Bell feverishly
pursued the harmonic telegraph his backers wanted and the telephone which
was now his real interest. Seeking advice, Bell went to Washington D.C. On
March 1, 1875, Bell met with Joseph Henry, the great scientist and
inventor, then Secretary of the Smithsonian Institution. It was Henry,
remember, who pioneered electromagnetism and helped Morse with the
telegraph. Uninterested in Bell’s telegraph work, Henry did say Bell’s
ideas on transmitting speech electrically represented „the germ of a great
invention.“ He urged Bell to drop all other work and get on with developing
the telephone. Bell said he feared he lacked the necessary electrical
knowledge, to which the old man replied, „Get it!“ [Grosvenor and Wesson]
Bell quit pursuing the harmonic telegraph, at least in spirit, and began
working full time on the telephone.
After llengthy experimenting in the spring of 1875, Bell told Watson „If I
can get a mechanism which will make a current of electricity vary in its
intensity as the air varies in density when a sound is passing through it,
I can telegraph any sound, even the sound of speech.“ [Fagen] He
communicated the same idea in a letter to Hubbard, who remained unimpressed
and urged Bell to work harder on the telegraph. But having at last
articulated the principle of variable resistance, Bell was getting much
On June 2, 1875, Bell and Watson were testing the harmonic telegraph when
Bell heard a sound come through the receiver. Instead of transmitting a
pulse, which it had refused to do in any case, the telegraph passed on the
sound of Watson plucking a tuned spring, one of many set at different
pitches. How could that be? Their telegraph, like all others, turned
current on and off. But in this instance, a contact screw was set too
tightly, allowing current to run continuously, the essential element needed
to transmit speech. Bell realized what happened and had Watson build a
telephone the next day based on this discovery. The Gallows telephone, so
called for its distinctive frame, substituted a diaphragm for the spring.
Yet it didn’t work. A few odd
sounds were transmitted, yet nothing more. No
speech. Disheartened, tired, and running out of funds, Bell’s experimenting
slowed through the remainder of 1875.
During the winter of 1875 and 1876 Bell continued experimenting while
writing a telephone patent application. Although he hadn’t developed a
successful telephone, he felt he could describe how it could be done. With
his ideas and methods protected he could then focus on making it work.
Fortunately for Bell and many others, the Patent Office in 1870 dropped its
requirement that a working model aaccompany a patent application. On
February 14, 1876, Bell’s patent application was filed by his attorney. It
came only hours before Elisha Gray filed his Notice of Invention for a
Mystery still surrounds Bell’s application and what happened that day. In
particular, the key point to Bell’s application, the principle of variable
resistance, was scrawled in a margin, almost as an afterthought. Some think
Bell was told of Gray’s Notice then allowed to change his application. That
was never proved, despite some 600 lawsuits that would eventually cchallenge
the patent. Finally, on March 10, 1876, one week after his patent was
allowed, in Boston, Massachusetts, at his lab at 5 Exeter Place, Bell
succeeded in transmitting speech. He was not yet 30. Bell used a liquid
transmitter, something he hadn’t outlined iin his patent or even tried
before, but something that was described in Gray’s Notice.
Bell’s patent, U.S. Number 174,465, has been called the most valuable ever
issued. If you have QuickTime or another way to view .tif files you can
view the document at the United States Patent and Trademark site (external
link). Search for it by the number. Each page of the six page document is
about 230K. And yes, it is very hard to follow. Patents are meant to
protect ideas, not necessarily to explain them . . .
The Watson-built telephone looked odd and acted strangely. Bellowing into
the funnel caused a small disk or diaphragm at the bottom to move. This
disk was, in turn, attached to a wire floating in an acid-filled metal cup.
A wwire attached to the cup in turn led to a distant receiver. As the wire
moved up and down it changed the resistance within the liquid. This now
varying current was then sent to the receiver, causing its membrane to
vibrate and thereby produce sound. This telephone wasn’t quite practical;
it got speech across, but badly. Bell soon ...
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