The radio is the clearest example in these histories of a machine already in existence—‘invented’—but not recognised as such. We have seen that the physicists of the world were intent on demonstrating the truth of theories promulgated by Maxwell and Helmholtz in the 1860s by using a variety of laboratory devices and how these had impacted on the development of the telephone, the phonograph and the gramophone (Figure 10). Their importance to radio is even more pronounced.
Hertz had conducted a series of experiments between 1886 and 1868 to demonstrate the existence of Maxwellian electromagnetic waves. He built a spark transmitter (or inductorium) and another device variously described as a resonator, responder, revealer, cymoscope or, more prosaically, a spark gap detector to detect them. In the transmitter, two rods with a small ball at one end and a large plate or ball at the other were connected to the terminals of a sparking coil. A spark was created which jumped the gap between the two smaller balls creating an oscillating current. The current produced electric and magnetic fields causing radio wave emission. The detecting device was nothing more than a bent wire in either a circular or square shape with a small break in it. The width of the gap could be adjusted using a screw arrangement. When the inductorium sparked, a small visible spark could be seen in this gap in the ring resonator (Phillips 1980:4-6). Despite the crudeness of the apparatus, Hertz was able to demonstrate that these ‘aetheric radiations’ did have wave-like properties and could, for instance, be reflected or refracted.
Hertz was not, of course, alone in this work. Curious electrical effects, the distant magnetising of needles following a Leyden jar discharge or a lightening strike had been noted in the 1840s. In 1875, Elihu Thomson of Philadelphia had detected a spark between a sharp pencil point and a brass door knob whenever a