""Catenary........... like the St Louis Arch, only upside down.""

I saw a nifty show about the arch on the History Channel.  The guy who
designed it actually hung chains in his basement to get the right catenary
curve.

It was built up as 2 towers that curved in toward each other.  Where they
met, there was a final 8' keystone to go between the two sides and link them.
 The sides ended up only 3' apart, though, so they had to jack the sides
apart to get the keystone in.  Not bad accuracy, considering the height.

Bill Marshall
'85 GL Tiico "Pandora"
Aurora, IL