Existence of dual mass: Linear theory

The field equations of general relativity are symmetrized in a manner similar to Dirac's symmetrization of electromagnetism. This symmetrization allows us to predict the existence of a gravitational, magnetic-like mass which we call dual mass. Time-independent solutions for both rotating and nonrotating sources are constructed for these generalized equations. The gravitational field produced by the dual mass source is compared with the gravitational field that follows from the linearized NUT and Kerr-NUT metrics, and an identification of the NUT parameter with a dual mass monopole is made.