6
$\begingroup$

So the story goes that in 212 BC Archimedes used bronze mirrors to incinerate Roman ships as they approached the harbor at Syracuse. This along with other ingenious inventions aided in keeping the Romans at bay until they were able to scale the walls of the city while it was distracted during their annual festival to the goddess Artemis.
Wikipedia: Siege of Syracuse

Subsequent attempts to prove or disprove the concept that Archimedes had indeed created and employed a “heat ray” using bronze mirrors have had mixed results. Some tests were concluded as positive, see e.g. Mythbusters were scooped — by 130 years! (Archimedes death ray) by Dr. Ioannis Sakkas, using sailors standing on the shore holding mirrors.

Others have concluded that while it’s possible Archimedes’ mirrors could ignite a ship it would be only under ideal conditions and that since the harbor of Syracuse faces East it would only work in the morning. This conclusion seems to indicate that it was unlikely that this was what was employed in Syracuse’s defense.
2.009 Archimedes Death Ray: Testing with MythBusters

That said, my question is at what point in human history (era or approximate years) would it be possible to create and deploy a “death ray” capable of instantly lighting aflame and sinking a wooden ship anchored at harbor a “bow shot” away? Additionally it would need to be capable of being employed against multiple ships either simultaneously or in rapid succession as would be required to keep such a fleet at bay. The death ray would ideally make use of solar power as that is what is typically described in Archimedes use of the “death ray”.

$\endgroup$
  • 2
    $\begingroup$ This short story by Arthur C Clarke, archive.org/stream/Galaxy_Magazine_Volume_16_Number_5_/… seems pertinent... $\endgroup$ – DJohnM Apr 18 '18 at 21:08
  • 1
    $\begingroup$ @PhilNDeBlanc they tried and "busted" it but then was proven wrong by some kids in high school that created working death ray. They showed successful results in next episodes. $\endgroup$ – SZCZERZO KŁY Apr 19 '18 at 12:34
  • $\begingroup$ I suppose it's much easier to ignite sail than wooden hull $\endgroup$ – ADS Apr 19 '18 at 13:08
  • $\begingroup$ @SZCZERZOKŁY Links, please? $\endgroup$ – user3106 Apr 19 '18 at 14:03
  • $\begingroup$ @JanDoggen I cannot find the episode but I've found this history.howstuffworks.com/historical-figures/… about MIT students. So it's probably about same thing. $\endgroup$ – SZCZERZO KŁY Apr 19 '18 at 14:52
6
$\begingroup$

It could have worked at any time that was able to produce bigger sheets of flat reflecting metal, or glasses with reflective metal coating. It's all about the heat flux: Incident power per surface area.

This was very relevant in firebombing, and nuclear bombing, so the military made some tests (Lawson, "Fire and the Atomic Bomb"):

55kW/m² will ignite fibreboard in 5 seconds

25kW/m² will ignite wood "after prolonged exposure"

The sun will easily provide 1kW/m², so ideally you would only need 25 pieces of 1.xm² mirrors (.x to account for the angle of incident sun to target vector and the non-perfect reflectivity, probably something like 1.5) and some time. The 1m² rays do not need to overlap completely, a smaller area where they all overlap would be enough. the suns beams are essentially parallel, so you will not have to account for natural beam divergence - big BUT coming up, though:

BUT: This also explains the neccessity of "flat" mirrors: The rougher or more bumpy they are, the less of the original ray will actually strike the target - you will need to have as flat a mirror as possible - glass cast on liquid lead or tin will be very flat indeed, but i don't know if that method is applicable in pre-industrial times.

A pre-industrial method might involve small pieces of metal made extremely flat, that are affixed onto a shield and individually positioned by an artisan (occlude all others, have the shield in a fixed position and then, at noon, glue the piece in place and light up a specific target a bowshot away while the glue settles. Repeat for all little pieces, then you have a shield thats very accurate. now repeat for 50 other shields - typical pre-industrial drudgery by specialists. If the shield-fixator was cleverly built, the reflecting angle of the shield (i mean the angle between the affixed points and the virtual surface of the mirror) would be known, and you could construct a mechanical device that angled all the shields for a specific sun inclination and target-vector (The neccessary individual angles are all a function of shield position (on device), sun position (relative to device) and target position (relative to device), and the mathematical function would be (easily?) modellable by levers). You could even have a (probably multi-person operated, because mechanical) joystick and target/sun sights (like on a sextant) to aim. Might be even better than having humans hold the shields individually.

If you are not into big mechanisms, consider this: have a target buoy bobbing around in the targeted area. Have a foundation for every mirror-shield, have an ironsight (= annulus near the eye, many beads strung into field of view) one person is at the sights. have a sun locator (a stick in the ground, with a design drawn around it so the shadow can be located) with person watching it. Now target the buoy by lighting it up with one shield at a specific sun location&target (=buoy) location. the shield-mover now can sketch the shield position for that sun location and target location. Next shield. Next. As the target bobs around in the harbor, and the sun walks over the sky, the shield-movers will sketch a lot of sun/target combinations. These will correlate, thus giving them the means to guess at configurations for un-trained sun/target combinations. On the day of battle, have the sun-guy and the target-guy call out their readings, everyone else just moves their shields to the pre-determined positions.If we determine a "bowshot" distance (as per olden sources) to be 200m, 1 degree of error will displace your ray by about 2 metres. With 1m-diameter rays we should stay below 0.5m error, so 0.25 degrees would be the maximal acceptable error. Is that achievable? For a circle 2m in diameter, 1° of circumference is about 2cm, so 0.5cm error for the tip of a stick attached to the shields. achievable, i'd say.

A pre-industrial source for ultra-flat surfaces might be crystals, but i doubt you'd get enough crystal-faces for the area needed. But even the ancient Egyptians had hand mirrors, and those definitely need to be flat, so i guess they had some experts that could make them that way. If you know of a method to get any hard substance really flat, you can always cover that in gold leaf (very ancient material too) and polish it, so pouring ceramics or something might work also, you'd just need one super-flat mould.

$\endgroup$
  • $\begingroup$ I bet your ignition numbers are for dry wood, not the wet wood of a ship. Your best bet would probably be to target the sails or rigging $\endgroup$ – Andrey Apr 19 '18 at 14:23
  • $\begingroup$ @Andrey: The cracks petween planks were often plugged with rags soaked in petroleum products or tree sap (both highly flammable, and by design non-wettable) - and a boat is not that wet above the waterline. - But yes, the numbers are not for wet material. $\endgroup$ – bukwyrm Apr 19 '18 at 14:38
4
$\begingroup$

While this is theoretically possible, there are a lot of practical issues with the story, and the number of attempts to replicate this have generally been negative.

Perhaps the largest problem is practically focusing the beam using multiple mirrors. While you could conceivably swing your mirror or bronze shield to reflect a spot onto a target, once a multitude of people are doing this, it becomes difficult to adjust "your" beam. The entire target may be brilliantly illuminated, but getting the proper focus on one spot long enough to reach ignition temperature for wood (between 190-260 degrees C) becomes extremely difficult. A modern device with can precisely hold each individual mirror in focus is possible, and solar furnaces have achieved temperatures of thousands of degrees.

I might suggest Archimedes cleverly used the blinding spotlight effect for more nefarious purposes: the ships crews could not see the defenders of Syracuse run up with small torsion catapults and fire flaming darts at the ships (if they were on the pier without cover, the Roman ships would have cleared the area using "Scorpions" mounted on the ships). The Romans would have been blinded by light then had fires starting on the ships, ships farther out might not be able to notice the darts but would see an association between the ships being suddenly lit up then catching fire.....

$\endgroup$
  • 2
    $\begingroup$ The second one is about the only thing that would work, ships are not that easy to ignite. Wood will smolder and smoke long before it ignites from just focused light and can be easily doused. using light to hide your defenders is a great idea andcould easily grow in the telling. $\endgroup$ – John Apr 19 '18 at 0:25
  • $\begingroup$ How much of the focusing problem do you think could be offset by good training? Considering the effectiveness of a random group of volunteers, a group of soldiers used to obeying orders, and a specialist unit trained for this particular exercise. $\endgroup$ – Separatrix Apr 19 '18 at 12:47
  • $\begingroup$ The problem is you need to see "your" spot and be able to guide it to the foal point among hundreds or thousands of other similarly moving and shifting "spots", all inside a very bright area where most of the "spots" are converging. Modern solar furnaces can use things like laser rangefinders, computerized guidance of the mirrors and a very solid frame to allow very precise fine movement of the mirrors to achieve that effect. Even highly trained soldiers with hand held mirrors would not be able to do so. Building a huge mirror frame on the edge of the harbour might achieve the effect. $\endgroup$ – Thucydides Apr 19 '18 at 13:58
  • $\begingroup$ Over stack your mirror unit so you have 2 or 3 times as many as you think you need for a moderately bad focus. Split them into groups of 8, each member of the group of 8 goes deliberately off focus in a specific direction to identify their own bright spot before coming back onto focus, keep doing this on rotation through the group. The end result should be a better average focus that you would get by massed hold and hope. $\endgroup$ – Separatrix Apr 19 '18 at 14:53
  • $\begingroup$ They (and by 'they' I mean Archimedes) should have been able to build some aiming mechanism, where the operator would have had a sight calibrated in function of the Sun position, shouldn't they? $\endgroup$ – Eth Apr 20 '18 at 16:09
3
$\begingroup$

The principle was understood but as Thucydides mentions there are targetting and focus problems once you build up high enough numbers of mirrors to have a significant effect.

So let's work backwards from more modern technology to help with that problem.

Consider a device, it looks a bit like a sextant. From one side you see the sun, on the other side your target. It's mounted on top of your mirror and moves with it. Your job as a solider of the 21st mirror battalion is to keep the image of the sun aligned with your target point on the image of the ship. You've trained for the past 6 months to be able to do this.

This requires relatively advanced optics and engineering, the sextant didn't come along until the 1700s, but the principle is sound.

For more basic technology consider two linked markers, when one shows/blocks the sun and the other shows/blocks the boat, your aim is correct (or at least good enough for government work).

Consider instead a mirror with holes in it, held a reasonable distant in front of you, eyes aligned to the centre, the holes are marked in 4 quarters, the sun is visible through one hole, the ship must be visible through the diagonally opposite hole for correct aim.

The idea here is to find some way for the individual soldier to accurately aim the mirror without having to identify their own personal bright spot on the ship, as soon as you've solved that problem the death ray becomes viable regardless of technological level.

$\endgroup$
1
$\begingroup$

Some solutions:
Use warped convex glass lens instead--ever fried a leaf with a magnifiying glass? If you used a lens large enough, it could set fire to something. As for timing: Quite early--types of natural glass already exist, and some types can be formed as a byproduct of metalworking. All you need, really, is (purepurepure) sand (silica) and maybe lime.
You could have mini ones for soldiers to carry around all the time, and then focus on a point from several places.
Try a Fresnel lens: curved ridges on the lens that help focus the sunlight more.
Use silver or aluminum--both are highly reflective metals. I imagine once you have a furnace big enough, you can make revolving plates to reflect/concentrate sunlight.
As for night technology: you would need to wait for electricity to come about, in which case you would use something like heat-generators or lasers. In any of these examples, you would need multiple lenses on swiveling turrets to take care of a ship. So perhaps station several groups on walls or coasts? I'll update this as I come up with more ideas.

$\endgroup$
  • $\begingroup$ The problem with using warped glass is that it has a limited focal distance, the principle of this is to use large numbers of moderately sized flat mirrors to simulate the effect of a much larger curved mirror with variable focal distance. $\endgroup$ – Separatrix Apr 19 '18 at 12:44
  • $\begingroup$ I'm not clear on where the lenses would be relative to the ship, in your scenario: Would they not need to be between ship and sun? $\endgroup$ – bukwyrm Apr 19 '18 at 14:42
0
$\begingroup$

Now.

enter image description here
From https://inhabitat.com/energy-breakthrough-storing-solar-power-with-salt/

Mirrored surfaces in computer-controlled mounts track the sun, keeping it aimed on the target. It's not that much of a stretch to make the mirrors be mylar drums who's "concaveness" can be controlled by vacuum pumps, and aimed at a ship at sea, not a central tower.

It would require lots of servo controls and constant tweaking of all the mirrors as the ship bobs up and down, back and forth, or even sails away, but computers are definitely capable.

Not that it would be practical. A flight of Exocet missiles would be a lot cheaper...

$\endgroup$
0
$\begingroup$

With regard to the problem of aiming the output of individual flat mirrors at a common distant target:

A common element in a survival package is a two-sided flat metal mirror with a small hole in it. The instructions for reflecting sun light to a target are :

  1. Hold the mirror so that you are can see the intended target through the hole;

  2. The sun shining through the hole will put a spot of light on your face/neck/chest. Find that spot of light by looking at the mirrored back-side of the metal mirror;

  3. Without changing Step #1, tilt the mirror around until the spot of light on your face/neck/chest "disappears" into the hole in the mirror

You are now reflecting sunlight towards the target.

Note:

In a multiple person attack scenario, you would not need to see "your" spot of light on the target. nor pay any attention to what your co-attackers are doing

The geometry and physics needed to prove this technique requires only simple Euclidean concepts (angles in intersecting straight lines), and basic physics (angle of incidence equals angle of reflection).

An individual attack mirror would need only a small mirror on the back-side, mounted parallel to the front-side mirror.

This technique has been addressed, with diagrams in this SE answer: https://outdoors.stackexchange.com/questions/15998/how-do-you-aim-a-signal-mirror

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.