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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: O.T. Math help
References: <3DC7C3FF.7ABC2433@webaccess.net> <3DCB3310.C806A8AE@rica.net> <%0wz9.21822$Ku.firstname.lastname@example.org>
Date: Sun, 10 Nov 2002 21:49:03 GMT
NNTP-Posting-Date: Sun, 10 Nov 2002 13:49:03 PST
Jim Thompson wrote:
> On Sun, 10 Nov 2002 19:39:58 GMT,
> "Michael Painter" ,
> In Newsgroup: sci.electronics.design,
> Article: ,
> Entitled: "Re: O.T. Math help",
> Wrote the following:
> |"James Meyer" wrote in message
> |> On Sun, 10 Nov 2002 17:16:21 GMT, Jim Thompson
> |> wroth:
> |> >"Mike" ,
> |> >Wrote the following:
> |> >
> |> >|
> |> >|He also states that the estimated time for a 1m tall, 1cm thick sheet of
> |> >|glass to flow enough to thicken the bottom of the pane by 10A is roughly
> |> >|billion years.
> |> >|
> |> >|-- Mike --
> |> >|
> |> >
> |> >I certainly can't debate the technology issues, but I've seen the
> |> >windows; and any tour of old sites, such as Williamsburg or Jamestown,
> |> >will have a tour guide or a placard noting the flow of glass.
> |> >
> |> > ...Jim Thompson
> |> Where else would you expect to see an "old wives tale" than an old site
> |> like Williamsburg or Jamestown?
> |> Besides, if I were an ancient glazier I think I would set a pane of
> |> glass that already happened to have a thick edge with the thick edge at
> |> bottom of the opening. It would only make sense to put the strongest part
> |> the bottom.
> |Possibly. It just occurred to me that nobody every talks about the material
> |at the top of the glass being thinner or the ripples in the glass changing.
> |You may be right about putting the thick side down, but I wonder if some or
> |all the edges might be thick?
> I don't know who to ask... my really old relatives keep dieing :-(
> (I had a great aunt, died at age 108 when I was 16... she could
> remember Lincoln coming thru on the campaign train when she was a
> But I have to ask... what makes you think 1600's era glass was the
> same as today's? The windows I saw were cloudy, perhaps implying a
> glass somewhat less pure than we know today, and probably made at a
> lesser temperature.
Old glass is a low melting glass. Typically "soda-lime" glass. The
cloudyness could be failure to cool through transition quickly enough or
it could be impurities in the sand used to make the glass. I expect it
is fairly green as well. The green comes from iron. In borosilicate
glass melts such as pyrex the green is evident and comes from iron
ladles but optical glass is rarely colored in this way. Sheet pyrex is
usually uncolored as well. Window glass and bottle glass is very similar
to the original soda-lime glass. Lab wear and cook wear is usually
borosilicate glass or a glass ceramic similar to zerodur. Optical glass
has a wide range of compositions giving index of refraction from about
1.47 all the way up to at least 1.95. Abbe number (relative dispersion)
varies from near 20 up to about 90. An Abbe number of 50 is the
arbitrary line separating crown glasses from flints. If I recall
correctly, "crystal" is a high index lead glass with a fairly low Abbe
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com
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