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@jasoncrawford | |||||
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So, let's say it's the 1840s, and you're tasked with building a suspension bridge at Niagara Falls, spanning a gorge almost 800 feet across and over 200 feet deep.
How do you get the *first* metal cable across? pic.twitter.com/pnMqOgfoa9
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Jason Crawford
@jasoncrawford
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5. sij |
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Here's one method:
1. Start by getting a light string across the gap, any way you can—one method was archery.
2. Use that string to pull a heavier string across.
3. Repeat with heavier and heavier cords/ropes/cables until you have one of the desired strength in place.
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Jason Crawford
@jasoncrawford
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5. sij |
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This “bootstrapping” method works well, but there was a challenge facing Charles Ellet, Jr., the engineer in charge:
No one could shoot an arrow across the 800 feet.
What to do instead?
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Jason Crawford
@jasoncrawford
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5. sij |
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Solution: Fly a kite!
Even better: Organize a kite-flying contest and have lots of people attempt to fly it for you.
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Jason Crawford
@jasoncrawford
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5. sij |
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Ellet offered a prize of $5 (about $150 in 2020 dollars). It was won by 16-year-old Homan Walsh, who, according to David McCullough, “would tell the story for the rest of his days.”
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Jason Crawford
@jasoncrawford
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5. sij |
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Once the first cable was across, Ellet, a consummate showman, demonstrated its safety by climbing into an iron basket suspended from the cable and pulling himself across, becoming the first man to cross the gorge.
(Basket shown here on display at the Buffalo Historical Society) pic.twitter.com/MHruYSYPdJ
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Jason Crawford
@jasoncrawford
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5. sij |
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This story is told in David McCullough's book The Great Bridge (which is mainly about the Brooklyn Bridge; Niagara is just a bit of backstory). It's also given here, with more detail: blog.ferrovial.com/en/2016/02/the…
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Jason Crawford
@jasoncrawford
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5. sij |
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Images in this thread are public domain and can be found at en.wikipedia.org/wiki/Niagara_F…
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Jason Crawford
@jasoncrawford
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6. sij |
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PS: Ellet's bridge only lasted 5 years before crashing. This was common back then! People didn't know how to build suspension bridges, and many engineers didn't trust them. John Roebling, who designed the Brooklyn Bridge, pioneered safe, sturdy suspension bridges.
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(((Charlie Martin)))
@chasrmartin
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6. sij |
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Drop a long wire down to the water level on one side. Drop a really long wire down to the water level on the other side. Get a couple guys in a rowboat to row across pulling the really long wire. Tie them together. Et voila
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Jason Crawford
@jasoncrawford
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6. sij |
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In this case the bridge was over some violent rapids. Boat was not an option
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