Originally posted here by The3ntropy

Just a little add on about the glass : In some old european castles the windows that have remained intact, are actually noticably larger on the bottom due to the fact that they are 'melting' away.
Actually, it turns out that the larger on the bottom windows was just a side effect of the way they created windows (The builders had the presence of mind to put the heaver end down)
The page from the usenet physics FAQ:
http://math.ucr.edu/home/baez/physic...ass/glass.html