dpb wrote:
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.

This is commonly heard but...

Probably because public school "science" teachers are taught it and pass it
along and while kids don't get anything _useful_ out of those "science"
classes they do get the notion that glass is not a solid. I recognized that
as bull**** the first time I heard it--the teacher gave a definition of
"solid" which glass met in every particular and then said "glass is not a
solid", but could not explain why it was not a solid and could not explain
what it was other than "glass" like "glass" is some fifth state of matter.

The notion that it's not solid is really a philosophical debate about the
definition of "solid" and has little do to with the realities of structural
design.

Corning Museum of Glass Research Scientist's discussion is at--
http://www.cmog.org/dynamic.aspx?id=294