Abstract: It is known that for a charge particle in a magnetic field，the Poisson bracket or commutator of dif- ferent components of the momentum is proportional to a component of the magnetic field.It is demonstrated that it is proportional a component of the mechanical angular momentum. This new relation can be considered as a manifesta- tion of Maxwell's qualitative statement that magnetism is essentially rotational in nature.

Key words: magnetic field, rotation, momentum, angular momentum, Poisson bracket