RE: [Killietalk] Siphon

["Hladky, John" <John_Hladky at tdytsi.com>]

Thanks Wright, very interesting.

I learned about "flowing glass" in a physics class during my undergraduate
work.  The prof went on to say that mirrors in large, old telescopes have
become slightly deformed leading to fuzzy images.  I wonder what it is about
human nature that make us gullible enough that such a myth would so imbed
itself in our minds that even a physics professor, who should know better,
would spread the story before checking it out.    
John Hladky



-----Original Message-----
From: Wright Huntley [mailto:whuntley at verizon_net]
Sent: Tuesday, January 20, 2004 2:52 PM
To: killifish discussion list
Subject: Re: [Killietalk] Siphon


John,

Hladky, John wrote:

> Chris,
> It is common knowledge that glass, being an amorphous solid, actually,
given
> time, flows...

Pure myth. Amorphous and solid, but no flow.

> 
> WOW!  I don't want to open that can of white worms again.  I still have
> heartburn from the crow I ate last time I brought it up.  Hey, this would
> make a great episode for "Myth Busters"!!!

Agreed. Here I come. :-)

I ran the precision glass shop at Hewlett Packard.

I then ran a company for 30+ years that made precision glass scales. One 
of my customers built them into an optical-disk-mastering machine with a 
precision and repeatability of 40 nanoinches (one nanometer). We knew 
glass was stable and did not flow.

To the best of their ability, the researchers at Ferranti found that 
unstressed glass was more stable than our knowledge of the velocity of 
light, back in the 60s. Because it is amorphous and doesn't undergo the 
same crystalline phase changes of metals, it is about the most 
physically stable substance known to man. It took many years to learn 
how to nitride and grind metallic gage blocks so there was enough 
external skin compression for them to be as stable. Until then, they 
used to shrink at a rough rate of 1 microinch per inch per year and 
required constant recalibration or certification.

When very old plate-glass windows (actually early float glass, I think, 
that had then been ground and polished) were examined, the bottom edge 
was always considerably thicker than the top edge, so some naive 
reporters assumed the glass had slumped over the years. It turns out 
they didn't know diddly. The glass was deliberately made that way, for 
it made for a stronger, lighter store window to have the bottom edge, 
carrying the weight, thicker.

> John in Huntsville
> 
> -----Original Message-----
> From: Chris [mailto:cgraseck at optonline_net]
> Sent: Tuesday, January 20, 2004 1:01 PM
> To: 'killifish discussion list'
> Subject: RE: [Killietalk] Siphon
> 
> 
> 
> What is it about old glass that makes it difficult to drill.  Has the
> glass changed over time or is our modern glass less brittle.

There are several answers to this question, Chris. Try cutting old glass 
shelves, for example. They are *made* very tough, with chemistry and 
edge shape, to resist breakage when you drop a medicine bottle on them. 
Getting a nice clean cut is very difficult.

Old windows, through many years of daily temperature fluctuations tend 
to become better annealed and hence maybe tougher to cut. They often 
were made by grinding and polishing (plate glass) which could be tougher 
than float glass (most modern windows) to cut, too.

There's probably no single reason, but generally old glass *is* probably 
a little harder to drill and cut (and easier to accidentally break in 
the process).

Wright

-- 
Wright Huntley -- 760 872-3995 -- Rt. 001 Box K36, Bishop CA 93514

"If people are basically evil, the last thing you'd want is a big
government staffed by those evil folks exercising control over you."
   -- David Bergland



To join the AKA see http://www.aka.org/pages/join.html
Archives are at http://fins.actwin.com/killietalk/

To join the AKA see http://www.aka.org/pages/join.html
Archives are at http://fins.actwin.com/killietalk/