Thomas Edison

B

The Phonograph

While working on the telephone, Edison also worked on perhaps his most original invention. He had noticed how the phone’s diaphragm, a thin membrane in the mouthpiece, vibrated in tune with the voice. He thought that if these vibrations could somehow be recorded, so that the diaphragm could be made to vibrate in exactly the same manner at any future time, then speech, music, and other sounds could be preserved and reproduced. Edison tested the strength of the diaphragm vibrations by holding a needle against the diaphragm with his finger, so that the needle pricked his finger with a force that varied with the loudness of the sounds.

In a later experiment, he applied one end of the needle to the diaphragm and the other end to a strip of waxed paper. He then pulled the paper along underneath the needle while repeatedly shouting, 'Hello!' The needle, activated by the vibrations of the diaphragm, created grooves in the paper. When the paper was again pulled along underneath the needle, the needle followed the grooves it had formed earlier and pushed against the diaphragm, making the diaphragm reproduce Edison's shouts. This first crude experiment, performed in 1877, marked the beginning of the phonograph.

Edison obtained a patent on the phonograph in February 1878. By this time he had replaced the waxed paper with metal cylinders covered with tinfoil. He postponed further development of the phonograph, however, for some years.

C

The Incandescent Lamp

After patenting the phonograph, Edison set out to develop an incandescent lamp, which would produce light by heating a wire until it glowed brightly. People already used electric arc lights, which produced light by creating an arc of electricity between two wires. However, the blinding glare these arc lights gave off made them unsuitable for home use. Edison, like others before him, conceived the idea of a light with a glowing wire, or filament, made of a substance that could endure very high temperatures without fusing, melting, or burning out. After hundreds of trials and more than a year of steady work, Edison developed a high-resistance carbon-thread filament that burned steadily for more than 40 hours. Although not the first incandescent electric light, it was the first practical one because it used a small current and, in addition, lasted a long time without burning out.

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D

Electric Power Distribution Systems

Edison realized that widespread use of electric light bulbs would require an efficient system of delivering electricity to homes and businesses. He developed detailed plans for an entire distribution system for electric power. This system included generating the current by means of a central dynamo (device that turns mechanical energy into electricity) and then distributing it in small quantities to thousands of homes and commercial buildings. Edison even developed a greatly improved dynamo to reduce the cost of generating electricity. The system Edison suggested in 1879 included the parallel circuits, safety fuses, insulating materials, and copper-wire networks used in modern electrical systems.

By 1881 Edison had set up a complete electric lighting system at his Menlo Park home. That same year his system took top honors at the Paris Electrical Exhibition in France. In 1882 at Holborn Viaduct in London, the Edison Electric Lighting Company completed and began operating the first commercial generating station for incandescent lighting in the world. This installation used an underground main and feeder circuit to supply power for 2,000 lamps. Later in 1882 Edison established the first permanent incandescent light and power station for private consumers, called the Pearl Street generating station, in New York City.

E

The Edison Effect

While Edison was working on the electric light, he made a scientific discovery that would become important to future generations. Edison noticed that particles of carbon from the filament blackened the insides of his light bulbs. This effect was caused by the emission of electrons from the filament, although Edison made the discovery before he and other scientists knew the electron existed. Not until 1897 did British physicist J. J. Thomson prove that the blackening observed by Edison was caused by the emission of electrons. This so-called Edison effect became the foundation of all modern electronics. Radio, television, radar, and computers all depend on it.

In 1884 Edison received a patent for a device based on the Edison effect. The device was designed to indicate variations in the output from electrical generators. The indicator proved ineffective because obtaining a good vacuum in devices at that time was difficult, but this was the first patent for a device that made use of the emission of electrons. It marked the beginning of the field of electronics.

IV

Glenmont

In 1884 Edison's first wife died of typhoid fever, and thereafter the inventor rarely returned to his laboratories at Menlo Park. After his second marriage in 1886, Edison bought Glenmont, a large country estate in West Orange, New Jersey, where he established a new laboratory. He remained there for 45 years. Glenmont and the laboratory are preserved as part of the Edison National Historic Site in West Orange and are open to the public.

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