  We consider a bound system of particles interacting via electromagnetic
forces in an external electromagnetic field, including leading relativistic
corrections. Each particle has a definite mass, charge, spin, and charge
radius. We introduce suitable canonical transformations and a perturbation
scheme to obtain a Hamiltonian which describes the global dynamics of the
system. This enables the derivation of formulas for various electromagnetic
moments, such as the magnetic dipole moment, the mean square charge radius, and
the electric dipole polarizability.
