Bell candlestick telephone design, c 1878.
© Science Museum / Science & Society Picture Library
In this instrument, soundwaves vibrate an iron diaphragm at the base of the handset, which in turn varies the magnetic field of the bar magnet. These magnetic fields then produce different currents in the coil. The 'candlestick' design and shape, evolved due to the false belief that a longer magnet would prove stronger. However, this simple design could function as a mouthpiece or earpiece. Internal view.