The gyromagnetic ratio of the proton

Certain nuclei can for many purposes be thought of as spinning round an axis like the Earth or like a top. In general the spin endows them with angular momentum and with a magnetic moment; the first because of their mass, the second because all or part of their electric charge may be rotating with the mass. Even the neutron, which does not have a net charge, has an electromagnetic moment. (The electro-magnetic moment is a vector quantity, the vector product of which with the magnetic flux density is equal to the torque). The quotient of the electro-magnetic moment to the angular momentum, called the gyromagnetic ratio, would be calculable if to each element of mass were associated a corresponding element of charge, but as the value thus obtained turns out to be very different from the measured value, roughly 5.6 times smaller in the case of the proton, we conclude that our knowledge of nuclei is not yet adequate for the calculation of the ratio. As however the nuclear gyromagnetic ratio γ, especially that of the simplest nucleus, the proton, enters into many relations between atomic constants, its determination is a matter of some importance.