Liquid microphones, invented by Alexander Graham Bell and Thomas Watson, were among the first working microphones to be developed, and they were a precursor to what would later become the condenser microphone. Early liquid microphones used a metal cup filled with water and sulfuric acid. A diaphragm was placed over the cup with a needle on the receiving side of the diaphragm. Sound waves would cause the needle to move in the water. A small electrical current ran to the needle, which was modulated by sound vibrations. The liquid microphone was never a particularly functional device, but it makes a great science experiment [source: Pemberton].