2013 Reprint of 1865 Edition. Full facsimile of the original edition, not reproduced with Optical Recognition Software. One of the unquestioned triumphs of nineteenth century physics was Maxwell's discovery of the equations for the electromagnetic field. "A Dynamical Theory of the Electromagnetic Field" is the third of James Clerk Maxwell's papers regarding electromagnetism, published in 1865. It is the paper in which the original set of four Maxwell's equations first appeared. The concept of displacement current, which he had introduced in his 1861 paper "On Physical Lines of Force," was utilized for the first time, to derive the electromagnetic wave equation.