One of the earliest contributions to the accumulated knowledge of insulation was made by Siemens in 1864, when he determined that an alternating voltage when applied to a capacitor resulted in a loss in the dielectric of the capacitor. Since then, various scientists and engineers, including Maxwell, Hopkinson, Pellat, von Schweidler, Wagner, Whitehead, Miner, and others, have contributed to the present state of theoretical knowledge of insulation and dielectrics.