One of two telephones used by Alexander Graham Bell in a demonstration that took place between Boston and Salem, Massachusetts on November 26, 1876. Critical features are the iron diaphragm (seen as a black circular disc mounted on the vertical wooden support), two electromagnets (seen in white, facing the diaphragm) and a horseshoe permanent magnet (lying horizontal, pressed against the electromagnets).
When used as a transmitter, sound waves at the mouthpiece cause the diaphragm to move, inducing a fluctuating current in the electromagnets. This current is conducted over wires to a similar instrument, acting as a receiver. There, the fluctuating current in the electromagnets causes the diaphragm to move, producing air vibrations that can be heard by the ear. This was a marginal arrangement, but it worked well enough to be employed in the first commercial services in 1877. The magneto receiver continued to be used, but the transmitters were soon replaced by a carbon variable-resistance device designed by Francis Blake and based on a principle patented by Thomas Edison.
Used in fiber optic repeater (1982.0529.01). A GTE terminal light source for an optical repeater set on a circuit board. One lead connects the board to electronics which in turn feeds a light emitting diode connected to an orange plastic insulated glass fiber. Printed on board: "G.T.E. Laboratories / C.O. Light Source Mod". Dymo label reads: "TLS". Using this equipment, GTE opened a fiber-optic telephone line between Long Beach and Artesia, California, in 1977. The transmitter employed a light-emitting diode (LED). Later systems would use lasers." Reference: http://www.sil.si.edu/Exhibitions/Underwater-web/uw-optic-05.htm.
Used in fiber optic repeater (1982.0529.01). A GTE optical repeater set on a circuit board. Seven leads connect the board to the unit which in turn feeds an orange plastic insulated glass fiber. One label reads: "Property of GTE / 47-3T1-034 / Laboratories", second label reads: "Property of GTE / 111-374 / Laboratories". Dymo label reads: "TLA". Using this equipment, GTE opened a fiber-optic telephone line between Long Beach and Artesia, California, in 1977. The transmitter employed a light-emitting diode (LED). Later systems would use lasers." Reference: http://www.sil.si.edu/Exhibitions/Underwater-web/uw-optic-05.htm.
Light emitting diode (LED) in a metal canister. Coaxial connector on one end, plastic covered tip on other. Written on canister: "C9". Used on terminal light source board for fiber optics repeater (1982.0529.04)
Photodiode detector in a metal canister. Three leads on one end, plastic covered tip on other. No extant makers markings. Used on terminal light amplifier board for fiber optics repeater (1982.0529.03).
Used to secure fiber optic cable to a LED on a terminal light source, or a photodiode on a terminal light amplifier in an optical repeater (1982.0529.03 and .04). A metal block with a V-shaped grove running lengthwise. Grove is covered by two metal and one ceramic plates. Threaded mounting holes are underneath. No extant makers marks.
Mahogany base mounting a glass tube containing iron filings -- a brass cased striker, a sounder, and relay. Marked "L.E. Knott Apparatus Co., 16 Ashburton Place, Boston, Mass." When a radio signal passes through the tube, the metal filings "cohere" or link together, closing an electrical circuit. Tapping the tube causes the filings to disassociate, opening the circuit. This was one of the earliest forms of radio signal detectors.
Telegraph relays amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.
This relay was made by John Polsey & Company of Boston, a firm better known for making clocks. Polsey (1816-1873) established the firm about 1859 and closed it in 1864. Western Union Company donated the relay to the Smithsonian in 1904 and reported that the relay was "a relic of the Confederacy and was used at Fort Sumter by W. R. Cathcart, manager for many years of their Columbia, SC office who was stationed at that fort as a military operator."
An optical repeated for use with a fiber optics telecommunications system. A steel mounting plate secures two 1" diameter cables on top and protects an electronics package below. Plate secures to a heavy metal canister (not included with the object). Label on top reads: "GTE Lenkurt / 91170 01 / Issue 3 M1".
Marked: "Ambassador / Tower Mfg. Co. / Brookline, Mass. / 3000 Ohms. / Double Set". Low impedance double headphones with headband, cloth-insulated cord, and pin plugs. One unit is broken from supporting rod.
