Tonight we are watching (old, I think) programmes about engineering and related topics. Mostly I have been tuned out but one caught my attention.
Top Gear’s Richard Hammond is breaking out on his own in the series Engineering Connections, and doing lots of engineering-related stuff. He’s at the Keck Observatory on Mauna Kea, Hawaii.
Richard has just got some of the scientists to test out a theory. Greek mathematician and general smarty pants Archimedes, once towelled dry and re-clothed (presumably), apparently built an array of bronze mirrors and used it to focus the sun’s rays on an invading fleet of enemy Roman ships, setting them on fire.
The current-day test used a smallish mirror, about the size of a Sky satellite dish, and a dinghy-sized wooden boat shape. The mirror was focussed on the boat shape and eventually, the boat caught fire. They surmised that this supports the Archimedes story. The thing was, the mirror was about a metre away from the boat, and the boat was sitting on a frame on the ground (ie not moving). As Hammond pointed out, if Archimedes had been that close to the invading fleet, they would probably have got quite cross and have stabbed him.
I did a little bit of googling and discovered that Mythbusters had already tackled this problem, and busted the myth. While in theory an array of mirrors could reflect the sun at a temperature of up to 600 degrees, the Mythbusters team could not generate more than 300 degrees, and this was not enough to set fire to the half-trireme they had built. Also, even to get the temperature of the wood of the ship to raise at all, it had to be about half the distance from shore. And finally, the temperature was raised only when the ship was not moving.
So, Archimedes had to have got the Roman fleet to park up a metre or so off the dock and wait for half an hour while he focussed his mirrors on their wooden ships. Presumably they would have been raping and pillaging around Athens at the time, and having popped back to find their ships burning, Archimedes’ career as a mathematician would have been abruptly cut short.
Tags: Archimedes, death ray, mirror arrays, Mythbusters