  The paper discusses the influences of velocity curl and field strength on
some theorems in the electromagnetic field and gravitational field. With the
characteristics of the algebra of quaternions, the theorem of linear momentum,
conservation of linear momentum, and conservation of angular momentum etc. can
be deduced from the quaternionic definitions of physical quantities. And the
strength of gravitational field and electromagnetic field have an influence on
some theorems directly. While the velocity curl has an effect on some theorems
also.
