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Alexander Graham Bell: Electrical Transmission of Articulate Speech, 1912

Photo- and Graphophone

The Photophone

In 1880, the French Government awarded Alexander Graham the Volta Prize of 50,000 francs (worth roughly $10,000 at the time) in recognition of his invention of the telephone. Bell put this money to good use, setting up the Volta Laboratory in Washington. This workspace would witness the development of two significant inventions: the photophone and the graphonphone. The photophone allowed for the transmission of sound on a beam of light, a precursor to modern day fiber optics, and Bell believed this device to be his most important invention. He used the photophone to transmit the first wireless telephone message on June 3, 1880.

Bell's photophone used the property of a selenium crystal that made its electrical conductivity dependent on the intensity of its light exposure. The transmitting light beam was created from sunlight by a system of mirror, lens, and a cell to remove heat radiation. The light rays shone on a motion-sensitive mirror which picked up and reacted to sound vibrations. Motion of the mirror created distortions in the light beam it reflected towards a parabolic mirror and this mirror focused the distorted light on the selenium detector at its center. The detector reacted by creating correspondingly interrupted electrical signals. These signals were sent to the magnet of the telephone and converted back to sound in the receiver in the usual way through an electromagnet connected to a diaphragm.

The range of Bell's photophone never extended beyond a few hundred yards, and the device also failed to protect transmissions from outside interferences, such as clouds. These outside interferences disrupted transport by blocking the beams of light necessary for transmission. The principles of the photophone were used by Guglielmo Marconi when he successfully developed wireless telegraphy.

The Graphophone

Originally known as the phonograph, the graphophone was developed in the interest of recording and reproducing sound. This was first achieved by Thomas Edison in 1877, and in 1879 Alexander Graham Bell and his apprentice, Charles Sumner Tainter, began making improvements on Edison's invention. Bell first became interested in the phonograph as a potential aid for teaching the deaf. He found, however, that the tinfoil records used by Edison to record and reproduce sound deteriorated after several uses. Bell and Tainter set out to investigate why this was so, and to ameliorate the problem.

The principle behind both the phonograph and the graphophone was to record speech vibrations onto a disk. Charles Tainter used a lighter substance than Edison for the recording disk, finding that a wax record cut with a chisel-shaped stylus was able to reproduce high-pitched sounds better than Edison's tinfoil record. Tainter cut the wax laterally, producing a zigzag pattern that controlled the vibration of the needle used to play the record. This was found preferable to the up-an-down action of Edison's needle. In the end, Tainter and Bell were unable to produce a fully functional graphophone, and Tainter concluded that their attempts at lateral cutting had failed because the zigzag grooves were too large and their pickup too heavy for the energy of the sound waves.

Tainter and Bell were under a time crunch to make improvements on the graphophone and file patents to take credit for those improvements before Thomas Edison could do the same. Unfortunately, their work was interrupted in 1881 when President Garfield was shot and they worked alongside other scientists to develop an instrument to locate and dislodge the bullet. In order to prevent Edison from finding out about their work and to assure themselves rights to a patent in case someone leaked information, Tainter and Bell packed all their work on the graphophone into a tin box, dated and sealed the box, and placed it in a vault in the Smithsonian Institution. These efforts were somewhat in vain, as success in lateral cutting was ultimately achieved in 1887 by Emile Berliner.1

1Source: http://history.acusd.edu/gen/recording/graphophone.html#group05