Spin and New Physical Field

It is shown that the interactions between the fermion and the gravitational fields are due to the torsion field. The torsion field is considered to be a potential one, like the electromagnetic and gravitational fields. The field equations are obtained, which describe the interactions of the torsion field with the conventional physical fields. The general covariant Lagrangian of the gravitational field, based on the torsion field, is derived. Experiment is proposed to test the theory.