A vindication of the Reverend Mr. Alexander Osborn, in reference to the affairs of the north of Ireland : in which some mistakes concerning him (in the printed account of the siege of Derry, the observations on it, and Mr. Walker's vindication of it) are rectified : and a brief relation of those affairs is given so far as Mr. Osborn, and other n.c. ministers in the north, were concern'd in 'em /