Coil system for the production of three-component uniform magnetic field at the Nurmijarvi Observatory

Following the design by Alldred and Scollar, a three component coil system composed of three sets of four square coils was constructed. The lengths of the sides of the smallest coils are 1.7 m and of the largest coils 2.3 m leaving enough room in the middle for working with the instruments to be tested. The homogeneity of the field was figured in different parts of the volume and found to be better than one part in 10 (exp -5) within a sphere of about 30 cm in diameter for the 2.3 m coil. Drawings showing the isolines within the coils are given. The homogeneity of the fields of the real coil systems were also measured experimentally and found close to the theoretical ones.