"In dealing with problems about electrons according to quantum mechanics, one finds one does not get agreement with experiment if one assumes the electrons to be simply point charges repelling one another according to the Coulomb law of forces. It is necessary to make the assumption that each electron is spinning and so has an internal angular momentum, and also that it has a magnetic moment. To make the theory agree with experiment we must assume that the eigenvalues of the Cartesian component of the spin angular momentum in any direction are ½\hbar and –½\hbar, and that the magnetic moment of the electron (with its sign reversed) always lies in the same direction as the spin angular momentum ..."