  The relation between symmetries and conservation laws for solitons in a
ferromagnet is complicated by the presence of gyroscopic (precessional) forces,
whose description in the Lagrangian framework involves a background gauge
field. This makes canonical momenta gauge-dependent and requires a careful
application of Noether's theorem. We show that Cartan's theory of differential
forms is a natural language for this task. We use it to derive conserved
momenta of the Belavin--Polyakov skyrmion, whose symmetries include
translation, global spin rotation, and dilation.
