Helmholtz Coils for Producing Uniform Magnetic Fields

The “Helmholtz coil” is really a pair of coils so proportioned as to produce a magnetic field uniform in magnitude and direction over a large region. The theory of the magnetic field produced by such a coil is briefly developed and the final (series) formula is put into a form convenient for calculations. For ordinary applications only the field at the center is required. A convenient design, developed for obtaining soft x-ray potentials by determining the velocities of ejected photo-electrons, is described, and is further explained by photographs and drawings.