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Episode 46: Archimedes Death Ray Revisited

Archimedes Death Ray: busted (again)

archimedes death ray

NOTE: all thumbnail images from MIT 2.009 page

The MythBusters already did their (failed) attempt at an Archimedes Death Ray, so this episode was framed as a contest for other people to make their own attempts. One contest was a "short range" contest to create a mirror that worked at 5 ft and the other was a 100 ft contest. By the end of the episode, the contest had become irrelevant as the contestants were sidelined by the news that MIT's 2.009 (Product Engineering Process) class had ignited a dry boat mockup at 100 feet in 10 minutes using127 glass mirrors. They MythBusters invited the MIT team out to make their attempt.

The MIT team got nothing more than smoke at 150 feet and only achieved ignition once it closed to 75 feet. Perhaps the 2.009 professors should have listened to the 5 minute technical feasibility they had the students do in class: 95% of the 80 students didn't think it would be possible.

The MythBusters really wanted to emphasized the 'bustedness' of this myth, so there were seven reasons given throughout the episode to back up their assessment:

  1. Compass: Syracuse faced east into the ocean, so Archimedes would have had to use morning rays for his weapon.
  2. Weather: mirrors only work when the sun is out
  3. Roman boats were moving: the death ray would have had to work quickly.
  4. 'Inflammable' sails: sails are difficult to ignite because of their light color and flapping.
  5. History: It wasn't until 800 years after the battle was that history books mentioned the use of mirrors.
  6. Scale: It would take quite a lot of people and mirrors to ignite a boat quickly.
  7. Alternatives: flaming arrows and fireballs are much easier to create, fire, and aim and also use much less manpower.

Myth: At the seige of Syracuse in 212 BC (during the Second Punic Wars), Archimedes built his 'burning mirrors,' which was an arrangement of mirrors that was capable of focusing a ray of sunshine on approaching ships and setting them aflame.

In the MythBusters' own attempt last season, they only got up to 290 degrees, which wasn't enough to ignite their mock Roman trireme.

archimedes death ray

The challenges

The episode was initially setup as two challenges: a 5ft death ray and a 100ft death ray. The contestants wereba judged on: * Creative use of materials * Relative to Archimedes myth * Actually sets things on fire * How good they are at making a video

Adam (referring to one of the contestant entries): "I feel like I'm watching something I didn't mean to find"

For the small scale category they accepted two entries: * Carrie and Jess (UCSB engineering students): they lit a piece of balsa wood on fire with a hexagon mirror array. * Brendan Millstein (Lawrence Berkeley) and Stephen Marsh (Harvard): guys who found a parabolic mirror in a box.

They also added their own entry, a giant satellite dish that they converted into a frame for 6000 1" square mirrors.

For the 100ft category they only accepted one entry, which was a NASA guy (Mike Bushroe) who created a variable focus mirror out of steel coated with silvering agent. This contest ended up being a bust at Bushroe's mirror didn't survive transport out to San Francisco (Mike: "Oh no, it's broken"). They showed it resurrected at the end of the episode, but didn't show any results from it.

Small scale contest

The contestants were given materials found in a Roman vessel to ignite: * wood * oakum soaked in pitch * pitch

In round 1, the Brendan and Stephen were allowed to use their parabolic mirror, which toasted all of the materials in nine seconds. The woman's hexagonal array of mirrors fared much worse, taking 2 minutes to ignite the wood and failing to ignite the oakum soaked in pitch.

Round 1 completely ignored their own contest rules, which stated that the material had to be ignited at five feet. With the real requirements re-instituted, they were given 24 hours to create new mirrors. Stephen/Brenden had to completely throw out their parabolic mirror, which had a much closer focal length. They ended up with two designs: plaster spun into a parabola and covered with reflective material and a pressurized drum covered with reflective mylar that was adjustable. Carrie/Jess bent their mirrors and re-aimed in order to meet the new requirements.

Brendan and Stephen were named winners, but neither really succeeded. Brendan/Stephen didn't ignite the wood, but they were able to light the hemp faster than the women.

The MythBusters entry appeared midway through round two, but it turns out that Jamie and Adam didn't pay attention to the rules and couldn't ignite at 5'. They ignited the oakum and pitch, but much closer than 5'.

MIT large scale entry

MIT's setup was the real focus of the episode. As part of the 2.009 Product Engineering Process class, Professor David Wallace and his students had successfully lit a dry mock boat using 127 glass mirrors at 100ft in under 10 minutes as part of a technical feasibility test (more info from the 2.009 web site). The MythBusters invited the class out to San Francisco to recreate their feasibility test, though they made them change the glass mirrors to bronze mirrors to stay accurate to the historical time period. The 2.009 class also would have to ignite a real boat in water, not a fake boat on a roof.

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archimedes death ray

Setup

The new setup called for 13 mirror holding stands and 300 bronze mirrors, which the MythBusters prepared.

Grant and Tory converted a boat into a mock Roman trireme using thick timbers coated in tar:

archimedes death ray

The Test

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MIT students aimed the mirrors in several minutes. It smoked a black spot into the side of the hull, but it couldn't ignite the hull. They realigned the mirrors to get 400 degrees up to 450 degrees at the focal point, but still no flames. Wallace got the MythBusters to move the boat so that they wouldn't have to readjust the mirrors.

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Wallace: "We need a bit of help. What we want you to do is reposition the boat so that we can get another pass at the part we've really charred"
Jamie : "So, what you're saying is that staying still isn't good enough? We actually have to move the boat for you into the line of fire?"
Wallace: "Shutup you lazy Roman pig and do what you're told"

They tried igniting the sail next as many viewers thought that this was more feasible. The sail didn't even smoke as the white reflected much of the heat and it was flapping in and out of the focal point.

archimedes death ray

The boat was brought within 75 feet for one final shot. Finally, the boat ignited.

archimedes death ray

The Finale

For their finale, the MythBusters brought out "The Scorpion," which was Grant's recreation of a known Archimedes weapon (animal sinew replaced with nylon rope springs). The Scorpion is a ballista (torsion catapult) that is effectively a giant crossbow. They shot lit arrows at the boat in what was probably meant to be a spectacular lighting, but Grant's first shot hit water and the next several shots did little to ignite the boat. Tory: "About twenty more of these and that's going up."

Jamie ended it all by dropped a large fireball into the boat to finally set it ablaze. Archimedes was said to be able to launch flaming fireballs 600 ft; Jamie is able to throw flaming fireballs about 20 feet.

Although the Scorpion didn't really work and Jamie tossed his fireball by hand, their point was that Archimedes had much easier means of setting boats aflame that didn't rely on the weather, tremendous manpower, tedious aiming of focal length, time of day, or any of the many other disadvantages of burning mirrors.

Wind knocked over many of their mirrors to finally bring the episode to a close.

mythbusted

Comments

hi. good job that you made the ship burn. we have to make a report about archimedes too. we want to burn a paper ship.
how do you recommened us to do it we planned to use mirror's and magnifying glass. would that work. please mail me if you have an idea

Hi,
Don't you think it would be possible for Archimedes to have, say 100 men (or women too) each HOLDING a mirror and on a given signal, focusing the light onto a certain point of a ship? That would take only a few seconds to concentrate the light and since they are holding the mirrors they could easily move with the motion of the ship. What do you think?

TO the last comment, just imagine trying to keep track and aim your stop of light with 100 others moving around in teh same area ^_^
They all look generally the same lol.

lets say you had a large scale parabolic mirror, adjusted to ignite ships at a certain radius around syracuse, which could be moved using a system of pullies, gears, or screws, remember, archimedes was pretty smart. Couldn't it be at least plausible that he made it work. I mean the guy was a genius with mathematics.

Consider this if you were trying to say that archimedes was able to burn a ship many many yards away:

1. he would need the ship be steady and not moving

2. the ship must be dry... but as you can see... travelling on the seas makes the boats WET, therefore hard to ignite

3. They needed strong sunlight

4. uninterrupting weather... no winds or rain etc...

5. A means that the people holding the mirror wont get killed during the process... perhaps arrows shot at them.

I just saw this mythbusters episode, why would anyone try to ignite the wood , when a much thinner and frail target, the sail, is available?

@Jason: they tried igniting the sail, but the sail moved around too much to maintain a good focus on it.

I was wondering if maybe the aim of Archimedes excercise was not to set fire to the ship but to disorientate the rowers and crew or any archers or soldier by blinding them with very bright light and generally just make life unpleasant enough that they would go away. There is no way that sunglasses were around then and I doubt if navigation would have been easy with 100 mirrors blinding you. The other point is that he had an army of disciplined soldiers to aim his mirrors, not a lot of people who are joking and not doing a proper job of it. With a good commander they may have been much more "focused" at their task. With the years passing the whole story may have gotten embellished and it seems as if the ships got burnt.
Its an interesting problem irrespective

There was a greek historian who tested this successfully in the 1960s or so and it was filmed. The footage was showed as part of a 3rd episode of a document called Ancient Discoveries, produced produced by Wild Dream Films/S4C, UK. It was shown on Finnish YLE TV1 on the 22.11.06.

I have some thoughts similar to DRW. The true aim of the mirrors could have been to disorient the soldiers on the ship. Furthermore, I believe we are underestimating the effect this would have had on a person of this time. Its easy today to watch the ship begin to smolder and assume that the experiment failed in igniting the ship. But what effect would this have had on soldiers of the day? With no understanding of the thermodynamics at work, I can easily envision a Roman soldier jumping overboard because he thought the gods were attacking him. To them, it would have been much more impressive (than to us) and this could have been elaborated over time. BTW, I have seen the show JB is referencing. That is why I am surprised by your results.

@Rich: They tried that with 8 people and failed.

@noshmoe: They had a large scale parabolic mirror in the show.

@DRW+the genius: Adam discusses that: "Maybe it is just to fear them away...Oh, bright light...sail away!".

@JB: It's in the show. Grant and Jamie discuss that too and they explain exactly, why he was wrong!

Adam did make a reference to the "bright light, sail away!" I am a teacher of Latin and History, and I spend a couple days analyzing Archimedes in my Ancient Warfare class. I agree with the assumptions above, that suggest the intention of the mirrors was more havoc then torching. The ships would have been trying to put suppressing fire on the walls as they approached them, with the intention of using scaling ladders to climb up. The mirrors could have blinded the Roman soldiers on deck (slaves underneath rowing), while Greek catapults could have sent amphora of burning pitch onto the ships. In the subsequent confusion and 2,222 years of history, the truth has been obscured. And, given there was a state of war between the Syracusans and Rome, it would have been pretty easy to find and polish the inside of a couple hundred concave Greek shields.

I happened to stroll by the scene of the battle the other day.

They used the mirrors to cover up the presence of archers with fire arrows.

As the boats was sliding into the harbour, the captains of the ships called all hands and archers on the ship was standing by to fight off counter attackers in boats and archers on land trying to set the boats on fire.

A man on shore stood up from behind a rock with bow and lit fire arrow. Just as the archers on the first ship was about to kill the man, a group of men and women also stood up and directed mirrors so that the archers on the ship was blinded and unable to aim properly. Arrows were shot, but they killed no one.

It certainly looked as if the mirrors shot fire, but I saw the fire arrows clearly.

Just figured i'd tell you guys that White sands missile range has a mirror bank like this they used for nuclear flash testing. It burned a 4" hole in a cast iron frying pan.

It suprises me that no one mentioned man-made atmospheric effects! While weather and clouds are mentioned, smog and ozone depletion are not. Mane made factors have certainly caused dispersion of the solar spectrum. Also, as MIT mentions, Oak was only used for the frames in the keel, the bulk of the plankwork would have been cedar or cypress (woods with much lower flash points!) Also, in Mythbusters and in the MIT test the woodwork is 2-3 in thick. This does not jive with a historical sailing vessel, which would have used much thinner wood in order to cut weight and increase speed (remember, no motors!).

I'd like to see an array of bronze mirrors focused at a 3/4" plank of cypress

The Mythbuster's forgot one simple point. The mirror's should have been focused on the sails. Once they catch fire, the boat cannot move.

Did they use the same material for the rigging that Romans' used? Dried ropes (or hemp or whatever material was used) may be more flammable than that used in the test. If the rigging caught fire, it would quickly spread to the sale itself.

Christopher Jordan's paper The Math Behind Burning Mirrors shows how to make & use the mirrors of Archimedes time. These were just small portions of spherical reflective surfaces made with a pendulum. They were able to deliver 500Mw/Sqm at 50m and that will vaporize stone or metal.

Regs

Will

Jamie$Adam I think Archimedes stating ONE BOW SHOT AWAY, for a realy good reason. If you heat wood till it smokes and then shot it with a flaming arrow the wood will burst into flames.This myth is confermed!!!! THANK ALL OF YOU FOR ALL THE FUN!!!!! phil

As to point #1 (Syracuse faces East) Though it is on the Eastern Coast of Sicily, there are harbor areas to the south of the peninsula that Syracuse straddles as well, this bay is much better protected from the Mediterranean, and the most likley location for the antique harbor.

I have been thinking about the aiming problem and come up with the idea of a sight to be on, or to be moved to, each mirror. The sight would be basically hole (a centimeter or so in diameter is good) in the mirror surface through which the person aiming can look and aim through a small shade positioned a few decimeters sunwards of the mirror with a hole almost as big as that in the reflecting surface. Aiming is done by looking through the hole in the mirror at the point on the object you want to illuminate, then moving the mirror so that the hole in the shade is in line and if the size of the hole in the shade is right, there will be a thin, symmetrical ring of illumination all around the hole in the shade: you are now aligned.
In my tests i have used CDs and the disks from a magnetic HDD (these are really great mirrors, glass or aluminum coated with highly polished (magnetic) metal. They have holes in them already of appropriate size and easily clip onto the top or side of a mirror becoming almost perfectly parallel with the mirrored surface.
With a hole in a card suspended by a wire support 30 cm in front of the sighting mirror I can easily aim my mirror to any spot within 90 degrees left or right of the direction of the Sun. Of course the better the Sun, mirror and target are aligned, the more solar energy hits the target from that mirror.
It does take some practice and a moving target would be a challenge. Not insurmountable by a populace intent on saving their city and culture.
I believe that the real deterrent in the case of the defense of Syracuse (if in fact this was attempted) was the heat and blinding light experienced by the crew of a Roman ship from a hillside populated by scores or hundreds with bronze mirrors - not ships bursting into flames... When it gets to be over 55 degrees Celsius you do not hang around long!