the myth that glass is actually a liquid comes from the fact that old windows in houses and churches (200–300 years old) are sometimes a little out of shape: thicker at the bottom than the top. this is actually due to the process of glass making in the past which led to the glass pane being thicker at one edge than the other. it was sensible to install the windows with the thick edge at the bottom. sometimes a window can be found with the thick edge at the top of the window.