Abstract
An exact treatment is given of the stresses in a flat coil, and account is taken of the spacing between turns by treating the windings as a homogeneous anisotropic material. The results are discussed as a guide to the stresses in thick solenoids. This is followed by a treatment of the stability of the turns of a solenoid against spontaneous deformation, using the principle of virtual work, and criteria for stability are found. It is shown that, in the absence of elastic restraining forces, the outer turns of a thick solenoid would be unstable.