ABSTRACT
Writing in the Philosophical Magazine in 1844, J. P. Marrian published an account of a series of observations on acoustic phenomena in relation to electromagnetism. Marrian claimed to have heard a sound, apparently related to the generation of an electric current. After constructing a helix of copper, wound around an iron bar, Marrian set out to measure the conducting power of various metals. He published “A dynamical theory of the electromagnetic field” in 1865, giving an account of this calculation and confirming Faraday’s experimental claims. In this chapter, the author constructed a helix of thick copper wire, on the outside of which is another of a much thinner wire, with such an arrangement that they can be easily separated. In three bars of equal sizes, one of soft iron, one of hard steel, and the third a permanent magnet, no sensible difference in these effects could be detected.
