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From: lew@ihlpa.UUCP (Lew Mammel, Jr.)
Newsgroups: sci.misc
Subject: Still skeptical of glass as fluid
Message-ID: <2215@ihlpa.UUCP>
Date: Wed, 5-Nov-86 14:05:23 EST
Article-I.D.: ihlpa.2215
Posted: Wed Nov  5 14:05:23 1986
Date-Received: Fri, 7-Nov-86 09:37:21 EST
Distribution: net
Organization: AT&T Bell Labs, Naperville, IL
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There have been a number of anecdotal reports of sagging glass windows.
It occurred to me that large telescopes would make a good test case for
this purported phenomenon. The Mount Palomar mirror is old, massive and
its shape is subject to exacting scrutiny.  If a window can develop a
"noticable" shape change in a few decades, I should think the same
phenomenon would be well observed at Mount Palomar. If noticable means
1 mm, then the Hale telescope (It's at Mount Palomar, right ?) is
sensitive to changes one ten thousandth as great. So if it sagged 1 mm
in 50 years, the optical quality would be affected in a few days.

I know that its elastic response to gravity induced stress has to be
dealt with, so what about its inelastic response?

Lew Mammel, Jr.