NARRATOR：

Now listen to part of a lecture on the topic you just read about.

FEMALE PROFESSOR：

The claims that the burning mirror would have been impractical and technologically impossible are unconvincing.

First, the Greeks did not need to form a single sheet of copper to make a large burning mirror.

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.

The Greek mathematicians knew the properties of the parabola and so could have directed the assembly of many small mirror pieces into the parabolic shape.

Second, about how long it would take to set a ship on fire with a burning mirror.

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.

But the Roman boats were not made just of wood. There were other materials involved as well.

For example, to seal the spaces between wooden boards and make them waterproof, the ancient boat builders used a sticky substance called pitch.

Pitch catches fire very quickly. An experiment showed that pitch could be set on fire by a burning mirror in seconds.

And once the pitch was burning, the fire would spread to the wood—even if the ship was moving.

So, a burning mirror could have worked quickly enough to be an effective weapon.

Third, why bother with a burning mirror instead of flaming arrows?

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.

But you cannot see the burning rays from a mirror. You just see the mirror.

But then suddenly and magically a fire starts at some unobserved place on the ship.

That would have been much more surprising—and therefore much more effective—than a flaming arrow.