Jay Manifold is wondering who Vivienne is (I assume he's referring to this month's masthead image, or else it's a really weird question).
In many versions of the Arthur legend, Merlin is done in when he is seduced by a wicked woman who tricks him into revealing to her the secret of his deepest lair -- usually a cave of crystal. The woman then seals Merlin inside forever, which is why he's not around later on when things in Camelot start to turn for the worse. In Tennyson's telling of the legend, Idylls of the King, this woman's name is Vivienne. Thus, the picture above depicts her seduction of the old and weary mage.
Now, her name is not the same in all versions. Sometimes she is Vivienne; sometimes Viviane; sometimes Nynaeve or Nimue. Sometimes she is also the Lady of the Lake, other times not. These variations are part of what, for me, make the Arthurian legends so compelling.