Archimedes burning ships with mirrors

Jan 2015
2,881
MD, USA
#21
It is said that soldiers have used their bronze shields to achieve it on sails with concentration of thousands of soldiers on the defensive wall.
From my point of view it is possible.
But as has been said, shields will NOT focus or concentrate light, they DISPERSE it, because of their shape. Dan also pointed out that bronze will not reflect enough of the spectrum to ignite anything, regardless of the perfection of the surface. It has also been pointed out that sails would not have been used during an attack like that. Nor could you mass "thousands" of soldiers closely enough together on a wall to focus any light, since shields were 2 to 3 feet in diameter, so the troops would be spread over a mile or more.

It's a clever idea, and shows a fascinating insight, and I'd love to know how it was thought up, but frankly it just won't work within the stated parameters.

Matthew
 

Dan Howard

Ad Honorem
Aug 2014
4,355
Australia
#22
But as has been said, shields will NOT focus or concentrate light, they DISPERSE it, because of their shape. Dan also pointed out that bronze will not reflect enough of the spectrum to ignite anything, regardless of the perfection of the surface. It has also been pointed out that sails would not have been used during an attack like that. Nor could you mass "thousands" of soldiers closely enough together on a wall to focus any light, since shields were 2 to 3 feet in diameter, so the troops would be spread over a mile or more.
There is also the small problem of nobody actually using bronze shields during the time in question. Bronze and bronze-faced shields were pretty much gone by the time the Romans came on the scene. There would not be enough of them in any army to use in the manner described above.
 

Dan Howard

Ad Honorem
Aug 2014
4,355
Australia
#23
This reminds me of an interesting point: it is impossible to start a fire with moonlight using mirrors/lenses. You could have a lens in space the size of the moon and focus all the light from the moon onto a single point, and it still wouldn't be hot enough. The second law of thermodynamics prohibits it: you cannot use a body at a fixed temperature (in this case, the moon) to create a higher temperature (the one needed to start a fire). IF you could, you could use a mirror to make that hot point on the Moon, and you'd turn a body at uniform temperature into one with colder spots and hotter spots, which could in turn drive a heat engine. But it is impossible to extract energy from a single body at uniform temperature. That's, essentially, one of the formulations of the 2nd law of thermodynamics; the most inviolable of physical laws.
It is certainly possible using modern mirrors, automated tracking systems, and the sun. We do it today with solar-thermal arrays.
 
Mar 2018
724
UK
#24
With the sun, obviously, a child with a magnifying glass can do it. That's because the surface of the sun is hot enough to burn things. My (albeit, not very on topic) point is that with the moon, it is not. That's because the surface of the moon is not hot enough to spontaneously ignite things. I guess the wider point is that the bigger mirrors effects how quickly you can heat things, but not the maximum temperature you can reach! (Ignoring the fact that whatever you are trying to heat is cooling at the same time...)
 
Likes: Dan Howard
Mar 2018
724
UK
#25
And, to stay on topic, bronze mirrors not being perfect, they essentially "cool" the light that they reflect so that it can no longer ignite things. They turn sun light into something a bit like moonlight; more of them won't help beat the thermodynamics limit.
 
Jan 2015
2,881
MD, USA
#27
Livy wrote some time after the taking of Syracuse by the Romans. Is it possible that his source was simply wrong?
Well, it seems that it *was* wrong! I'm still curious how the story got started, though. Someone had to know *something* about focusing sunlight with mirrors, it sounds like. Doesn't mean anyone regulary set anything on fire that way, but...

Matthew
 
Feb 2011
1,039
Scotland
#28
Well, it seems that it *was* wrong! I'm still curious how the story got started, though. Someone had to know *something* about focusing sunlight with mirrors, it sounds like. Doesn't mean anyone regulary set anything on fire that way, but...

Matthew
Polybius, though slightly fragmentary here, lived much closer to the time of the siege (and would have been a source for Livy)

Whilst he details contrivances such as levers, pulleys and engines, he makes no mention of shields used to focus the sun's rays. Neither does Livy or Plutarch. Polybius lived close enough in time to have interviewed participants.

This source here Burning Mirrors- Refutation provides a detailed explanation of why the mirrors never happened.
It explains that the earlist source to refer to mirros specifically dates from as late as 500CE by Anthemius of Tralles and even he apparently says he is being imaginative.
 

Dan Howard

Ad Honorem
Aug 2014
4,355
Australia
#29
To summarise:
None of the popular sources, such as Livy, Plutarch, and Polybius, actually mention the use of mirrors to burn ships. They have been confused with later sources such as Anthemius (500 A.D.)
Bronze mirrors can't burn anything no matter how many you use because bronze doesn't reflect enough of the light spectrum. You need modern mirrors.
Metallic shields won't work because their surface is convex, not concave; they will disperse the light, not focus it.
Bronze shields stopped being used long before the alleged date of this battle.
It isn't possible for hundreds of men to reflect light all in one spot long enough to start a fire while the ship is constantly moving.
Even if sails were easier to ignite, the Romans never used sails during the attack, they used oars only.
 
Last edited:
Likes: benzev
Apr 2018
279
USA
#30
Somewhat related. In William Bourne's 1578 "Inventions or Devises", section 109 discusses how to various mirrors and glass lenses may be used to ignite fires from up to a mile away. The author seems to have done some experimentation with this and is apparently somewhat skeptical of the Archimedes story aside from suggesting that it would perhaps require fewer glasses to ignite a ship at a Mediterranean latitude than it does in England.

"
AS it is not vnknowne in respect vnto all persons, that you may burne any thing that is apt to burne with a glasse at hand, which is done by the Sunne beams pearsing through the glasse, for that the Sunne beames bee vnited and knit all together in the center thereof, which is the ve∣ry cause that it burneth, and as we doo reade that Archi∣medes burned the Romane Nauie at Syracusa in the Iland of Sicilia, some haue supposed that he did burne thē with such kind of glasses, which is most vnpossible: wherfore it must needes be, that they were burned with diuers glasses, and the reflection of the Sunne beames turned vnto them. But this is to be noted, that it is possible that fewer glasses may serue to burne any thing there in that Latitude, than that it will doo here in this Latitude, for that the Sunne beames be more hoter: for the Latitude of Syracusa is but fiue and thirtie degrees and a halfe, and to burne anything any great distance off with glasses, it requireth to haue some sight in Geometrie, or els it is not possible for to doo it, and for to burne any thing that is apt to burne, it must bee thus handled: they must prepare a number of glasses made of mettall, such as the common people call of steele, made of purpose, and well polished, and to place those glasses to burne, as if that it were gunne powder, flaxe or towe, or occom, pitch, tarre, or such like things that will take fire quickly, the Sunne shining very bright: then set the glasse against the Sunne, and then turne the reflection beame or shadowe to the place assigned that you would burne, and then place another glasse in the like manner, and turne the reflection beame or shadow vnto that place in like manner, right vppon the first ende of the beame or shadowe, and so to place more glasses, and to bee sure that all the reflected beames or shadowes doo rest vppon one place, and so by a great number of glasses to multiply the heate, that in the ende it will bee set on fire and burne: but you must be sure that all the reflected beames or shadowes doo rest in one place, or else it will be vnto no purpose, and at a great distance you shall haue much to doo to decerne or see it, &c. Wherefore you must haue the ayde of Geometry, to vse it according vnto the distance, and to place the glasses in a frame, which I doo omit at this time for breuitie.
"

https://quod.lib.umich.edu/e/eebo/A...itary+art+and+science+--++Early+works+to+1800

Anyways, a couple more thoughts on the topic if we want to give Archimedes the benefit of the doubt:

-The ancients around Archimedes' time do seem to have been at least aware of the concept of using mirrors to redirect and concentrate light. The lighthouse of alexandria for example is supposed to have used mirrors to help make its light much more visible to ships at a great distance.

-Even if bronze isn't very good at reflecting sunlight, could they have potentially used mirrors coated with some other substance such as polished iron, tin, or silver?

-I think i once had someone suggest to me that perhaps the defenders somehow first managed to coat the roman ships with a substance similar to the later Byzantine "automatic fire" which had a much lower ignition temperature. That's probably not as impressive as setting a wooden ship on fire using mirrors alone, but if you were just looking for a way to surprise the enemy or set them on fire at the right time from a distance that would probably be a plausable option.

Lastly, as for how the story may have originated. I'm not sure we can discount the possibility that it actually did occur or was at least attempted at some point, just not during the siege of Syracuse/by some inventor other than Archimedes, and that the story was later miss-attributed to Archimedes retroactively since he later generally became by far the best known brilliant-ancient-science-guy. As an alternate example, Italian mathematician Niccolo Tartiglia in 1537 came to the conclusion that "most skillful Philosopher and Mathematician" Archimedes was probably the first person to invent gunpowder.
 
Last edited:

Similar History Discussions