A phonometer is an instrument invented by

Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These invent ...

for testing the force of the human voice in speaking. It consists chiefly of a mouthpiece and diaphragm. Behind the diaphragm is placed a delicate mechanism which operates a 15-inch

flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, assu ...

by means of which a hole can be bored in an ordinary pine board.

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* American inventions Thomas Edison Physiological instruments {{measurement-stub