About 600 BC, the Greek philosopher Thales found that amber, when rubbed, had the property of attracting dry and light materials. As the Greek word for amber is ELECTRON, the property became known as ELECTRICITY.
In the 18th Century, Allesandro Volta found that two dissimilar metals, separated by damp salted paper, produced a continuous current at low voltage. From this developed the voltaic cells, which led to Faraday's experiments with magnetic and electrostatic fields - and to the mathematics of James Clerk Maxwell.
Daniell, Leclanché and Poggendorf voltaic cells provided the earliest reliable sources of electrical current. They later developed into the modern battery.
Early electromagnetic offspring included the Cooke & Wheatstone telegraph, the Morse key and the telephone. In 1887 German physicist Heinrich Hertz, using Maxwell's theories, produced a 'spark transmitter' which generated, transmitted and received electromagnetic waves, proving the existence of radio waves.
Discs of amber or glass rubbing rods were rubbed vigorously with a piece of fur and the charge taken off successively by an electrophorus - a piece of metal with an insulated handle. The electricity was then measured with a gold leaf electroscope, stored in a Leyden jar and the excess high voltage removed with discharging tongs.
In the late 18th century, this process was mechanised in the form of friction machines, of which Winter's machine is an example, and later, by influence machines such as the Wimshurst machine, which produced electricity in time separated, high voltage pulses. The induction coil produced high voltages and generated sparks by breaking down the air insulation. Induction coils were the basis of early radio transmitters.