A Helmholtz coil is a device consisting of two identical circular coils, spaced apart by a distance equal to their radius, and carrying an equal electric current in the same direction. This configuration creates a nearly uniform magnetic field in the central region between the coils. This Helmholtz coil apparatus consists of two 5 inch solenoids, each made of 44 turns of enameled copper around a plastic bobbin. There are two 4mm induction safety sockets for each solenoid to receive a maximum current of 7A from an external power source (sold separately). Also included with this set are a 26cm scale to measure the distance between the solenoids on their rails and a clamp to hold a magnetic field sensor or a compass (sold separately).