Ammeter Wattmeter for an alternative use for this instrument. Moving iron ammeters use a piece of iron which moves when acted upon by the electromagnetic force of a fixed coil of wire. The moving-iron meter was invented by Austrian engineer Friedrich Drexler in 1884. This type of meter responds to both direct and alternating currents (as opposed to the moving-coil ammeter, which works on direct current only). The iron element consists of a moving vane attached to a pointer, and a fixed vane, surrounded by a coil. As alternating or direct current flows through the coil and induces a magnetic field
Electrical telegraph working control of Western Union in 1909 but relinquished it in 1914 under threat of antitrust action. AT&T bought Western Union's electronic mail and Telex businesses in 1990. India's state-owned telecom company, BSNL, ended its telegraph service on 14 July 2013. It was reportedly the world's last existing true electric telegraph system. Electrical telegraph An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via dedicated telecommunication circuit or radio. The electrical telegraph, or more commonly just telegraph, superseded optical semaphore telegraph systems, thus becoming the first form of electrical telecommunications. In a matter of decades after their