BELL’S FIRST TELEPHONE: a parchment membrane that vibrated when sound waves hit it. A spring held a piece of iron so that it gently touched the membrane, and near the piece of iron was the pole of an electromagnet made up of a coil and the core of a magnet; when the parchment and the iron vibrated, the magnetic field of the magnet varied, inducing an electric current in the coil (FARADAY did this, 1791-1867). If two identical devices were connected, the current produced by one fed the electromagnet of the other, making its piece of iron vibrate and consequently the membrane attached to it, thus reproducing the sound waves produced by the voice. Thus, the transmitted sounds circulated in both directions, one of the characteristics that distinguished the radio from the telephone, another is that the radio does not use cables and the telephone does.