This device transmitted sound on a beam of light by projecting voice through an instrument toward a mirror. Vibrations in the voice caused similar vibrations in the mirror. Sunlight was directed onto the mirror, which captured and projected the mirror's vibrations. These vibrations were then transformed back into sound at the receiving end of the projection. The photophone's function was similar to the telephone, except the photophone used light as a means of projecting the information, where the telephone relied on electricity.
Over the years, the telephone and its accompanying system went through several transformations. The first telephone system (exchange), installed in Hartford, Connecticut in 1877, provided a means of communication between many people who have phones. The first exchange linking two major cities, New York and Boston, was established in 1883. The first exchange outside the United States was built in London in 1879, and was operated by a group of operators working at a large switchboard. Each operator sat in front of a bank of phone jacks attached to phone cords, each of which was attached to a subscriber line. When a calling party lifted their receiver, a light near the phone jack would activate, the operator would answer, ask for "number please?-, and plug the callers' line into the appropriate sending jack. Though this was the current method for connecting a call, it did not afford the caller privacy. The operator had many opportunities to listen to conversations. An undertaker in Kansas City, Almon Strowger, suspected that local operators were routing calls to his competitors. He invented an automatic telephone exchange in 1891, but manual switchboards remained common until the middle of the 20th century (Almon). .
Several more inventions and innovations have taken place over the years. In 1889, William Gray of Hartford, patented the coin operated pay telephone.
