The following omissions and misprints occurred in this paper: Page B109: the phrase following equation (6) should read `where h(R) is the specific angular momentum, Vh is ...'. Page B109: the gravitational constant G should be inserted in equation (10). Page B111: the quantity `Vr' preceding equation (17) should be replaced by `Va'. Page B111: the left-hand side of equation (17) should be replaced by Page B111: In the text following equation (17), `equation (9)' should be replaced by `equation (11)'.