| The Italian experimenter, Carlo Matteucci
(1811-1868), in experiments in the mid-eighteen forties, showed that the
effect worked over larger distances without the presence of iron. He devised
a pair of identical flat coils, with wire wound in a spiral pattern on
the surface of glass disks about 30 cm in diameter. A Leiden jar was discharged
through one of the coils, and an experimenter holding on to wires connected
to the other coil felt a shock. The magnitude of the shock increased when
the distance between the two coils decreased.
Matteucci is also known for his work with the electrical
conductivity of the earth in 1844. By demonstrating that the earth has
an appreciable conductivity, he showed that it was possible to use the earth
as a return conductor for telegraph signals, thus making it possible to
use one metallic conductor instead of two.