  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.
