Telecommunication
The conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849. However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London.
Ernst Ruhmer
Ruhmer first gained widespread recognition for his work on improvements to Alexander Graham Bell's optical wireless telephone, the photophone. Bell introduced this device in 1880, which used selenium cells in the receiver to convert the fluctuating light produced by the transmitting unit into sounds. But Bell's invention only had a range of a few hundred meters, and he soon ended his research into this device. Ruhmer believed that the increased sensitivity of his selenium cells, combined with the superior receiving capabilities of professor H. T. Simon's "speaking arc", would make the photophone practical over longer signalling distances.