Mythbusters did this very experiment. When they were doing a test with handheld mirrors, they had trouble even getting a dozen or so people to aim them all on one spot.
Later they built a huge rig with tons of mirrors aimed together (not handheld) to see if they could get a boat to light on fire. It didn’t work.
This. A stick would also work and make it easier. Just rest your mirror on the ground place the stick so the tip of it is on the line from the center of the mirror to the target and you are in. As long as you see light on the tip of that stick, you know you are hitting your target. I was really pissed at the Mythbusters’ half assed attempt at this one.
But with WHAT accuracy?
If the stick is at 10 feet and your target is at 500 ft, then a half inch error at the stick becomes a 25 inch error at the target. Unless you have a BIG and FLAT mirror, that kind of error is going to seriously cut in the the “concentration” you are trying so hard to achieve.
It has been done. According to legend, a ‘philosopher’ whose name I forget burnt Roman ships besieging Syracuse with parabolic mirrors. A few years ago the Greek navy decided that since the Romans wrote the account they didn’t know what he’d used and had probably lined men up on the city walls with polished shields. So they got some sailors together to see if it was possible with metal mirrors to represent the old shield and trained the sun on a model boat. It caught fire.
Archimedes. He’s been mentioned in pretty much every link posted in this thread. The burning glass is somewhat disputed, but it’s universally agreed that he did make a variety of very effective weapons for the defense of Syracuse.
Yeah, this is exactly the myth they were testing on Mythbusters, which I mentioned a couple posts ago. They decided it was impossible.
Why? What did they do wrong?
It seems to me that you can pretty much divide the attempts at re-creating the Archimedes legend into two camps: artificial attempts using some or all of modern materials, unrealistic distances, unrealistically still targets. These attempts sometimes work. Then there are realistic attempts which all fail due to various impracticalities.
Sorry – I’ve been away all day, and haven’t been able to answer.
1.) There are several methods of aligning a mirror so that you can reflect sunlight onto a distant target. This is, as noted above, the basis of the heliograph. During the second world war, the Air Services and the Navy were concerned that people on life rafts would want to be able to signal for help with mirrors. GE included such mirrors in their emergency kits. Two articles by R.S. Hunter in the Journal of the Optical Society of America (Vol. 35, pp. 805+ (1945) and Vol. 36, #2, pp. 110-115 (1946)) told how to use them (After the war was over, unfortunately).
2.)There were several methods described, but the two simplest were those given by 1920s Death Ray and by Chronos. Death Ray’s (appropriate!) is the more obvious, but the method Chronos gives is more elegant, and doesn’t require you to stick out something blocking part of the beam. This method is also described by Albert Claus in Applied Optics Vol. 12, #10, p. A14 (1973) and in Hal Clement’s science fiction novel Cycle of Fire (1957). Arthur C. Clarke describes something similar in his short story “A Slight Case of Sunstroke” from 1958, which is in his collection Tales of Ten Worlds.
3.) I know that Mythbusters tried this and failed, but they really did a bad job of it. They didn’t use people individually adjusting mirrors, but made a big mirror out of small sections (which is actually what Archimedes was said to have done. The idea of using individually controlled mirrors was suggested later by another Greek, Proclus). But his method of adjusting the focus was pretty crude – they never checked them optically, as is evident from the huge size of the “focus”. Ideally, this ought not to have been larger than the reflected spot from a mirror, but it was much larger. (I’m told there was a followup, but have never seen it).
4.) The experimenthasp been carried out successfully, despite the Mythbusters’ failure. In 1973 Ionannis Sakkas of Greece got a team of 60 soldiers to direct sunlight using mirrors onto a ship 160 feet away (in the water) and set it on fire. The result was published (with pictures) in Time magazine, not to menion the London Times and in New Scientist. in 2002 a German team used 500 volunteers to ignite a sail 50 meters away. The Comte de Buffon had performed similar experiments back in tyhe 18th century. See Mlahanas’ website at Archimedes and his Burning Mirrors, Reality or Fantasy?
5.) Archimedes has been adopted as a sort of Patron Saint . of Adaptive Optics (even though, as I say, it was Proclus who used multiple movable mirrors). I’ve seen him cited by at least three works on Adaptive Optics (the engineering technique that uses “rubber mirrors” ) as the father of their discipline.
6.) I don’t really think that either Archimedes or Proclus was able to actually burn ships. I do think it was within their technical capabilities, but I doubt that they ever built the battery of mirrors needed or rehearsed the soldiers in the techniques. There are easier ways to sink a boat.
The 500 guys sounds about right, but again I imagine the situation was more optimum than realisitic. Particularly is you are talking about what the ancients could accomplish. No, not THOSE ancients.
The 60 guys? Some major cheating going on if I had to bet.
Then look at the distances. A measely 150 feet or so. A handful of guys with flaming arrows could do that. Longer and useful distances would be much harder alignment and aiming wise.
See my point #6 above. As I say, I dpubt if anyone ever actually did this in the ancient world, or if it would be worthwhile. But it’s certainly possible.
Oh, I generally agree with you agreeing with me agreeing with you…
The 60 guys one. Do you have any more info on that one? I suspect their target was either strike anywhere matches or they had large high precision long distance focusing mirrors.
I’ve seen the pictures – it looked like a respectable test, and it was on a boat made to look like an ancient Greek craft – not matches. I haven’t run he numbers, but I can believe that under a hot, clear Mediterranean sky, such as they had, they could concentrate quite a bit of light on a ship.
okay, but southern sunny florida aint now slouch either, and for normal materials I need something closer to a 500 times “intensification” than only 60 to start fires.
Of course we been having a cloud free heat wave for nearly a month here, and just NOW its gotten all cloudy on me
Very true. Although I guess that’s why 500 are better than 60. Find enough men and soon enough precision doesn’t matter much. Then again, you have to make 500 big flat mirrors and not just 60. Good luck finding a good mirror store in Ancient Greece.
Although I am not on the pro-Archimedes camp, I found the MB effort to be specially half-hearted. 9 people looking desperately like they would rather be anywhere else are hardly equivalent to disciplined and trained soldiers looking to defend their wives and children from an invading army. They set out to prove it could not be done and, surprise, they succeeded. A failure only counts when you set out to prove you can do something.
Keep in mind, too, Archimedes’ goal wasn’t to defeat a ship, it was to defeat an entire navy. Even if you could have taken out the ship with arrows, that just gets you one ship. Soldiers are used to arrows; they know what to expect. But if you take out one ship with a hillside of soldiers wielding the fire of the Sun itself, the next shipful isn’t going to want to stick around to find out just what the limits of your weapon are. From what I’ve heard, the Roman soldiers’ fear of Archimedes’ inventions was a major contributor to how Syracuse was able to hold them off for as long as they did.
Very true. Just starting any fire on the sails, supplies, etc or burning a couple of soldiers would be enough to sow all kinds of doubts on a superstititous bunch.
So apart from some vague waffle about motivation, you’ve got nothing.
You may have missed the part about numbers, training and discipline. 9 pencil pushers on a first try are no match to 60-500 trained soldiers.
I’ve been thinking about this so indulge me if you will.
The sun subtends about a one-half degree angle - about the size of a dime held at arm’s length. A flat mirror projects an image of the sun of the same angle so, regardless of the distance to the target, you would need to aim the mirror within one-quarter of a degree to hit a point.
The number of mirrors you need depends on the distance and the size of the mirrors. At 500m the sun image will be 4.4m in diameter with an area of 15 square meters. If each soldier’s mirror is 1 square meter then 15 soldiers will deliver one sun-power. A sun magnification of 500 times would require 7500 soldiers.
If the soldiers aim perfectly then the 500 sun intensity would be felt over the whole 4.4m diameter circle. In reality there would be a bell curve with the center point receiving the full intensity with diminishing intensity further away.
Numbers means something, perhaps, but just insulting people and waffling about training and discipline is meaningless unless you say what this training and discipline is actually going to result in, in terms of actual activity.