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第一段
1 .Now listen to part of a lecture on the topic you just read about.
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第二段
1 .The claims that the burning mirror would have been impractical and technologically impossible are unconvincing.
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第三段
1 .First, the Greeks did not need to form a single sheet of copper to make a large, burning mirror.
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2 .An experiment has shown that dozens of small individually flat pieces of polished copper could be arranged into a parabolic shape and form a large, burning mirror.
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3 .The Greek mathematicians know the properties of the parabola and so could have directed the assembly of many small mirror pieces into the parabolic shape.
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第四段
1 .Second, about how long it would take to set a ship on fire with a burning mirror.
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2 .The experiment the reading selection mentions assumes that the burning mirror was used to set the wood of the boat on fire, that's what takes ten minutes.
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3 .But the Roman boats were not made just of wood.
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4 .There were other materials involved as well.
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5 .For example, to seal the spaces between wooden boards and make them waterproof, the ancient boat-builders used a sticky substance called pitch.
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6 .Pitch catches fire very quickly.
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7 .An experiment showed that pitch could be set on fire by a burning mirror in seconds.
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8 .And once the pitch was burning, the fire would spread to the wood even if the ship was moving.
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9 .So a burning mirror could have worked quickly enough to be an effective weapon.
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第五段
1 .Third, why bother with a burning mirror instead of flaming arrows?
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2 .Well, Roman soldiers were familiar with flaming arrows and would have been watching for them and were ready to put out the fires they might cause.
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3 .But you cannot see the burning rays from a mirror; you just see the mirror.
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4 .But then suddenly and magically a fire starts at some unobserved place on the ship.
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5 .That would have been much more surprising and therefore much more effective than a flaming arrow.
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