From: "Russell Jocoy" 
To: atm{at}shore.net
Reply-To: "Russell Jocoy" 



("atm{at}shore.net")

   I found an old time/life book about the universe at a Goodwill store and
would like to share some
facts about the 200 inch mirror at Mount Palomar.
               The glass blank came from Corning glass works, it took 2
years and almost $650,000.00 all
spent in vain trying to cast a disk out of quartz. Pyrex was then chosen.
But a 200 inch disk would be
close to 42 tons and take 9 years to cool and anneal!!     To reduce the
mass a ribbed design was
chosen, which involved building a mold like a waffle iron with cores of
silica brick. Anchoring the cores
turned into a nightmare struggle with heat:  one disk was ruined in casting
when the steel anchor bolts
melted and the cores bobbed to the surface of a sea of liquid glass.
               Finally in December of 1934 a perfect disk was cast in 7
hours of suspenseful labor, and put into a specially built oven to cool. 
After 10 months, yes I said 10 months, of cooling it was sent on a
flatcar to California for the long job of polishing.  This disk was 20 tons
and had a 40" center hole.
       The polishing tool was faced with almost 2000 glass blocks about
4"x4".  Polishing was done
at the California Institute of Technology.  It took 11 years to polish this
monster, with the interuption
of war, and over 5 tons of glass were removed by 30 tons of abrasives
before the disk was ready
for mirroring.
                It took only one ounce of vaporized aluminum to coat  the
30,000 square inch surface.

     Just some food for thought............. RUSS JOCOY

("atm{at}shore.net")





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