# How to place window on second screen?

I am trying to open a window on a second screen (a thunderbolt display attached to a macbook pro) that is the full size of the second screen. Here is the command I use:

ThunderboltDimensions = {2560, 1440};
window = CreatePalette[{}, WindowSize -> ThunderboltDimensions,
WindowTitle -> None, WindowMargins -> {{1440, Automatic}, {Automatic, 0}}]


This opens a window that looks correct, except that the top edge is about half way down the display. In fact, no changes to the second part of the WindowMargins value seem to have any effect.

Am I missing something, or is this a bug? Is there a simpler way to specify a second screen? And why does 1440 work for the left edge (Mac Pro display width is 2880)?