It is shown that the first two terms in the expansion of the scattering amplitude of light by a system of spin ½ in powers of the frequency can be simply expressed in terms of the macroscopic properties of the system. The first term is the well known Thomson amplitude, and depends only on the total charge and mass. The second term is found to depend only on the charge, mass, and magnetic moment of the system.

• Received 13 August 1954

DOI:https://doi.org/10.1103/PhysRev.96.1428