On Dec 10, 6:50*am, Phisherman wrote:

Most glass is a liquid and sags. * In an old house you may see the
bottom of the windowpane is thicker than the top portion. * Quartz
glass is a solid--probably less sag over time and transmits more
lightwaves than regular glass.

I believed that for a long time until it was pointed out to me that
there are intact glass windows in Roman and Egyptian buildings which
would belie the flowing glass myth. If the glass sagged enough to be
noticeable in a two hundred year old house, the sag in two or four
thousand year old glass would be very noticeable, and it's simply not.

http://www.glassnotes.com/WindowPanes.html

http://dwb4.unl.edu/Chem/CHEM869A/CH...en/florin.html

R