sk was thrown into vibration, thus producing
sound. As it vibrated with the current produced by the iron on
the vibrating membrane in the transmitter acting as an armature,
transmitter and receiver vibrated in unison and so the same sound was
given off by the receiver and made audible to the human ear as was
thrown against the membrane of the transmitter by the voice.

The patent issued to Bell has been described as "the most valuable
single patent ever issued." Certainly it was destined to be of
tremendous service to civilization. It was so entirely new and
original that Bell found difficulty in finding terms in which to
describe his invention to the patent officials. He called it "an
improvement on the telegraph," in order that it might be identified as
an improvement in transmitting intelligence by electricity. In reality
the telephone was very far from being a telegraph or anything in the
nature of a telegraph.

As Bell himself stated, his success was in large part due to the fact
that he had approached the problem from the viewpoint of an expert
in sound rather than as an electrician. "Had I known more about
electricity and less about sound," he said, "I would never have
invented the telephone." As we have seen, those electricians who
worked from the viewpoint of the telegraph never got beyond the
limitations of the instrument and found that with it they could
transmit signals but not sounds. Bell, with his knowledge of the laws
of speech and sound, started with the principles of the
transmission of sound as a basis and set electricity to carrying the
sound-vibrations.

XIII

THE TELEPHONE AT THE CENTENNIAL

Boll's Impromptu Trip to the Exposition--The Table Under the
Stairs--Indifference of the Judges--Enter Don Pedro, Emperor of
Brazil--Attention and Amazement--Skepticism of the Public--The Aid
of Gardiner Hubbard--Publicity Campaign.

The Philadelphia Centennial Exposition--America's first great
exposition--opened within a month after the completion of the first
telephone. The public knew nothing of the telephone, and before it
could be made a commercial success and placed in general service
the interest of investors and possible users had to be aroused.
The Centennial seemed to offer an unusual opportunity to place the
telephone before the public. But Bell, like Morse, had no money with
which to push his invention. Hubbard was one of the commissioners of
the exposition, and exer