Gaugain-Helmholtz (?) Coils for Uniform Magnetic Fields

Abstract

THE use of two equal and co-axial circular coils of wire, separated by a distance equal to their common radius and traversed by the same electric current in the same sense, has long been the standard practice for producing a nearly uniform magnetic field throughout an appreciable volume. The question which seems unsettled is whether Helmholtz improved upon a device invented by Gaugain or invented the whole device by himself at an earlier date.