Interesting note about the line. I vaguely remember something about the meaning of different lines in art from a lecture I heard a long time ago. Thanks for the reminder, I'll have to look into that again!
Actually, I just got something more precise, here: ('A primer of visual literacy', page 46) Diagonals ...Has to do with the idea of stability. it is the most unstable directional force and consequently the most provoking visual formulation. It's meaning is threathening and almost litteraly upsetting. Much more accurate, this one Sometimes it's funny to have that kind of information. Very nicely done, anyways