The Development of Radio or Wireless Communication

Bell and Tainter in 1878 were probably the first to succeed in telephoning by "wireless" means.^10,24,25 Their device, called a "photo-phone," used a beam of light for conveying the talking impulses between two points.

Henry was among the first to experiment with electrical action at a distance without connecting wires.²⁷ By 1843 he had succeeded in magnetizing needles at a distance of 220 feet from the source.²⁶ In 1865 and 1873 Maxwell gave his famous papers on electromagnetic phenomena and showed mathematically that electric action is propagated through free space in the form of waves which travel with the velocity of light. In 1869 Ruhmkorff perfected a coil which for a number of years was used almost exclusively to supply the radio-frequency voltage for the antennas. In 1879 Hughes gave a demonstration of the transmission and reception of radio signals over distances of about 60 feet. He also discovered the principle on which the coherer - a detecting device later perfected by Branly - operated in wireless reception.^24,26 In 1883 Dolbear and in 1885 Edison both developed signal systems employing an elevated antenna and a ground connection. Also, in 1883 Edison applied for a patent on a two-electrode vacuum tube.

Hertz ranks with Maxwell in making outstanding contributions to the progress of radio communication. In 1881 Hertz published¹ an account of his experiments; he showed that rapid electrical oscillations

in conductors caused disturbances in space and that these had the characteristics of waves. Hertz worked with waves about 3 meters long and demonstrated that they could be reflected, directed, refracted, and polarized.²⁶