Bohr, Nils

Referring to the fundamental discussions between Albert Einstein and Nils Bohr, Wheeler writes ... 

We are dealing in our model with electrons in orbitals, which are defined to have both orbital motion and spin motion both contribute to the (para)magnetic moment. Quantum theory associates quantum numbers with both these motions. The spin and orbital motion of an electron in an orbital involve quantum numbers for both spin momentum (.S ), which is actually related to the number of unpaired electrons (n) as S = nil, and the orbital angular momentum (L). The magnetic moment (pi) (which is expressed in units of Bohr magnetons, pis) is a measure of the magnetism, and is defined by an expression (7.1) involving both quantum numbers. 

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