Page:A Treatise on Electricity and Magnetism - Volume 2.djvu/366

 729.] If we wish to suspend a coil between two coils placed so near it that the distance between the mutually acting wires is small compared with the radius of the coils, the most uniform force is obtained by making the radius of either of the outer coils exceed that of the middle one by $$\frac{1}{\sqrt{3}}$$ of the distance between the planes of the middle and outer coils.