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The space-space field equations of the Jordan Brans-Dicke theory describing a spatially homogeneous vacuum spacetime of the Bianchi type can be brought under transformation into a general set of nonlinear differential equations, an all-encompassing general equation implicitly contained in each of the cosmological models studied, most of whose analytic solutions the authors have found. The scalar field displays a considerable influence in the cosmological context during the early, strongly relativistic stage of the universe's expansion where the main difference between the cosmologies of Einstein general relativity and Jordan Brans-Dicke theories lies in the possible existence of a sourceless phi field which, since it is not generated by matter, is contrary to Mach's principle. Several solutions presented are reported for the first time.