Quite some time ago I wrote up a piece on how a vertically oriented mirror laterally inverts an image (it doesn’t by the way). People quite often ask, if a mirror inverts laterally, then why doesn’t it invert vertically as well. In other words, if a mirror inverts left-right, then why not top-bottom. That is an extremely good question as it turns out, and the answer carries on with the same theme of SYMMETRY. We get left-right inversion (or apparent inversion) when the mirror is positioned VERTICALLY. So what happens when the mirror is positioned HORIZONTALLY? The above image of the reflection of a tree in calm water (the mirror) shows you what happens. Yep – there’s the top-bottom inversion for all to see. Symmetry considerations can be an extremely powerful technique for solving some (apparently) difficult problems.
