Page:A Treatise on Electricity and Magnetism - Volume 2.djvu/344

312 If the transverse section of the coil is circular, of radius $$c$$, then, by Art. 692, whenceor, the mean radius of the coil should be $$3.22$$ times the radius of the transverse section of the coil in order that such a coil may have the greatest coefficient of self-induction. This result was found by Gauss.

If the channel in which the coil is wound has a square transverse section, the mean diameter of the coil should be $$3.7$$ times the side of the square section.