From slashdot: The Solar Death Ray.

Quoting the "about" section:


So if everyone in your party has a signal mirror... :-) :-)

So if we hear about Bountyhunter handing out signal mirrors to a kindergarden class...........

I seem to recall that in some naval engagement the ancient Greeks did something similar, using polished shields to set enemy ships ablaze.

Vince

There's more legend than fact to that story. It was soundly debunked on Mythbusters last season. At the required distance they were only able to raise the surface temps a 100 or so degrees. Of course, there is always the possibility that there was an alien intervention (the same ones that built the pyramids) and the whole polished mirror/shield story was just a cover for the conspiracy. I have no evidence to support this theory but that is precisely what defines a good conspiracy.

Ed

"At the required distance they were only able to raise the surface temps a 100 or so degrees."

Was that celcius or fahrenheit?

I wonder if that was hot enough to get the Persian sailors leaping into the water though? <img src="/images/graemlins/cool.gif" alt="" />

Vince

Eodman:

Also describes a perfect crime.

Bountyhunter

Farenheit I believe. <img src="/images/graemlins/blush.gif" alt="" /><==Persian sailor after being blasted by solar death ray <img src="/images/graemlins/grin.gif" alt="" />

I thought they used something called Greek Fire. It supposedly burns more when it comes into contact with water.
Sorta like a powdered aluminium and iodine crystal mixture. To make fire, just add water.

"Sorta like a powdered aluminium and iodine crystal mixture. To make fire, just add water. "


Why am I just NOW learning this?! <img src="/images/graemlins/ooo.gif" alt="" />

I enjoy reading about famous, historical personages of math and science. Some of these individuals were egoists and some were real people. I think the naval use of mirrors is attribuated to Archimedes and later written about by Diocles. The following has been taken from two longer web articles.

Diocles (240BC - ~180BC) in Burning Mirrors , proved that the surface that reflects the rays from the Sun to a single point is a paraboloid of revolution. Constructions of such devices remained of interest as late as the 6th century AD, when Anthemius of Tralles, the architect of the Hagia Sophia at Constantinople, compiled a survey of remarkable mirror configurations.

According to Roman writers who chronicled the life of Archimedes (287BC – 212BC), the mathematician was a devoted subject of Hiero II, ruler of Syracuse, and spent part of his career designing and building weapons to defend Syracuse -- catapults, pulley hoists and levers for disabling enemy ships and siege towers. … Some Greco-Roman historians also assert that during the Roman siege of Syracuse from 214 to 212 B.C., at the height of the Second Punic War, Archimedes used bronze mirrors to focus sunlight on Roman ships and set them on fire.

The burning mirrors are mentioned by Lucian of Samosata and Galen. Anthemius of Tralles (534), the Architect of the Hagia Sophia, tells us that Archimedes used many mirrors. Johannes Zonaras in 1118 says that first Archimedes used the "iron hand" against the ships and then he burned these with mirrors. http://www.mlahanas.de/Greeks/Mirrors.htm

Plutarch writes in his work on Marcellus, the Roman commander, about how Archimedes' engines of war were used against the Romans in the siege of 212 BC:

... when Archimedes began to ply his [war] engines, he at once shot against the land forces all sorts of missile weapons, and immense masses of stone that came down with incredible noise and violence; against which no man could stand; for they knocked down those upon whom they fell in heaps, breaking all their ranks and files. In the meantime huge poles thrust out from the walls over the ships and sunk some by great weights which they let down from on high upon them; others they lifted up into the air by an iron hand or beak like a crane's beak and, when they had drawn them up by the prow, and set them on end upon the poop, they plunged them to the bottom of the sea; or else the ships, drawn by engines within, and whirled about, were dashed against steep rocks that stood jutting out under the walls, with great destruction of the soldiers that were aboard them. A ship was frequently lifted up to a great height in the air (a dreadful thing to behold), and was rolled to and fro, and kept swinging, until the mariners were all thrown out, when at length it was dashed against the rocks, or let fall. http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Archimedes.html

Pete

"It was soundly debunked on Mythbusters last season."

I wouldn't rely on Mythbusters for science. Generally they try to reproduce one version of a myth, fail, and announce it "busted". In this case they were unable to control their focus well enough. More people, more training, and more time and experimentation could have helped. Mythbusters tend to be very restricted on time - they probably spent 3 days on this when the ancients would have spent years; and Mythbusters had about 20 staff where the ancients had armies of men to practice with. Scale matters.

There is more on this at the slashdot site. Interestingly, one of the problems is for each soldier to figure out which spot of light corresponds to his mirror/shield. Some kind of aiming mechanism, such as is used by a modern one-handed signalling mirror, would have helped. If they had such, it's been lost.

And unless you have access to a laser you will not be able to concentrate the light sufficiently to reach ignition temps on a wooden ship at distance. The Mythbusters fixed array consisted of >100 mirrors all aimed to a single point at a set distance. This configuaration was decided upon after having the staff try, and fail, to accurately aim the mirrors by hand. The tar sealed target was tethered at the requisite distance and no ignition was achieved. To have 100 troops, even well trained troops, hold aim on a single point on a moving target long enough to achieve ignition is not believable. Remember, this is not tinder being lit by the concentrated beam of a Fresnel lense at 6 inches. You're talking about large dimension lumber at hundreds of yards. If you choose to believe in this fantasy then I will leave you to it.
Ed

Mostly I'm warning against putting your trust in Mythbusters. If you have other reasons to disbelieve, that'#s fine. For what it's worth, you don't need a laser. Light from the sun is already as near parallel as makes no difference. The size of the mirror makes a difference. What the mirror is made from makes a difference. The number of mirrors makes a difference. The soldiers would have had more time for training, and more motivation, than Mythbuster's staff. I agree they might have used a better target than timber; the boat's sails, perhaps, or rope rigging.