  In contrast to charge vortices in a superfluid, spin vortices in a
ferromagnetic condensate move inertially (if the condensate has zero
magnetization along an axis). The mass of spin vortices depends on the
spin-dependent interactions, and can be measured as a part of experiments on
how spin vortices orbit one another. For Rb87 in a 1 micron thick trap m_v is
about 10^-21 kg.
