Heaviside versus Rolling

Historical Electromagnetic Theory

Ivor Catt 1 January 2009

It all began with the discovery by

Gian Domenico Romagnosi in 1802, or perhaps by Oersted in 1820, that if a compass needle was placed in the vicinity of a wire carrying electric current, it deflected. Thus, Oersted discovered that electric current caused a magnetic field. Later, in 1829 came Francesco Zantedeschi's (or perhaps Faraday's) twin discovery, that changing magnetic field caused electric current. These discoveries led to "Theory N"; that electromagmetic field was caused by electric current and voltage.

Fifty years later, Heaviside said; "We reverse this;" the electric current is caused by the electromagnetic field, leading to his "Theory H", and to Catt's "Theory C" a century later.

What is the effect of Heaviside's "We reverse this" to the original Oersted discovery? When Oersted though he had a wire carrying electric current, he actually had the wire (and return wire) guiding an electromagnetic field travelling between the wires at the speed of light. The original cause of the compass needle's deflection was an (electro)magnetic field travelling past the compass needle, which naturally responded to the magnetic field. Electric current was not involved.

At this point, it is easier to gloss over Zantedeschi's 1829 and 1830 "papers on the production of electric currents in closed circuits by the approach and withdrawal of a magnet", because "Theory C" does not treat the magnet, and move to Faraday's 1831 experiment which later became the transformer. " Faraday's breakthrough came when he wrapped two insulated coils of wire around an iron ring, and found that upon passing a current through one coil, a momentary current was induced in the other coil."

Unknown to Faraday, he did not introduce electric current into the primary coil. In fact, according to "Theory C", he introduced energy current, guided into the transformer primary by two conductors. This energy current, or electromagnetic field, partly became enmeshed in the seconday coil. The intermediary was not changing magnetic field, but electromagnetic field, or energy current. Throughout, only energy current, or electromagnetic field, was involved.