What I wonder is how they could amass such a huge navy on Onondaga Lake.
I assume you mean on Page 3.
(And is this an advanced case of “my post is my cite”? 
)
Since I include cites, no.
The problem with this approach: say one of the shields/mirrors is off focus - how do you know which one?
The MIT team got around this during alignment by uncovering mirrors one at a time, and aiming for a stationary target. However, if the target moved, then you would have to change the alignment of each and every mirror - a way of doing this in parallel (rather than serially) that would have been available to the ancients does not suggest itself to me. Neither does it seem practicable, given their technology, that there would have been an alignment/focus arrangement that would have steered a sufficient reflecting area to ignite a ship.
I know that you “can’t prove a negative” but this seems like an example of something that strains the bounds of believability.
Seems simple enough to me: Assign the troops a series of repeating numbers (much as the coach used to assign teams in gym class), then spread them out along the wall; at a command, every soldier with the number 1 shines his mirror away from the target, then “walks” it up to the target point; all the numbers 2 do the same thing, etc. Since each soldier is following his own reflected light until it gets into the target, he knows where it would be and would not be confused by other jiggling lights. It would not be perfect, and it might take a bit longer than desired for optimum effect, but it could be done.
And, as CalMeacham has noted, there are ways to"sight" mirrors.
I tend to agree that mirror ovens were not a weapon of choice at Syracuse, (mostly for the lack of evidence provided by jimmmy’s citations along with the lack of a good target on a ship of that era–especially with furled sails). However, I think the objection that the mirrors could not be aimed is overstated.
You know, if I were attacking Syracuse and knew about Archimedes, I’d be scared of what he’d pull out of his bag of tricks. Just seeing a mirror on the clifftop pointed at my ship would impair my efficiency considerably.
In other words, the stunt wouldn’t even have to work to have an effect on the battle.
I guess I should elaborate on my point a bit more - not that I totally discount the possibility of doing something in the manner which you describe.
Aiming reflected sunlight on a bright day to a distance of tens of meters is going to be tricky. As long as “your reflection” (meaning the one from your mirror) is on a dark target, you should be able to adjust its position. But if that reflected sunlight falls off the target and onto the surrounding water, it will be much harder (or impossible) to track that reflection. And it will likewise be hard to adjust your individual reflection precisely onto exact focus if several cohorts are trying to achieve aim simultaneously. The idea of several moving off focus at the same time, say each in a different direction, sounds fine, but once you get close to ideal focus (within one image-width of on-target), it will be harder to differentiate which relection goes with whose mirror. And this still assumes a stationary target - no wave motion while riding at anchor, let alone moving under oar-power. For ignition, you are going to need to either maintain focus for enough time or to concentrate sufficient solar energy. Time is your enemy since it gives the enemy ship time to move, the sun moves upsetting your aim, and the enemy sailors can respond by dousing with water. Scaling up is problematic for resource reasons, and because the time to achieve proper aim scales with the number of mirrors.
I’m basing much of this reasoning on watching video of the MIT attempt - in that attempt, aiming of the mirrors (and steadying them once aimed) was the crux of the problem, and their solution was serial-aiming at a stationary target. Now, I’m not one for bad-mouthing the ancients (or MIT, for that matter), but unless someone comes up with a more compelling demonstration I think the weight of evidence falls on the “didn’t do it” side, particularly given the other considerations mentioned (absence of historical record, relative expense of this method w.r.t. fire arrows, etc.)
And the trouble with 100 or 1000 soldiers holding mirrors is, well, those guys could be firing arrows.
Plus, warships of the era carried sails, but never used them in battle. Warships were galleys. There’s no way 100 guys can each keep a mirror trained on a moving warship.
I’m not sure about this, but I have a hunch that one could produce a simple sighting mechanism for each ‘shield’ (which I reckon would actually be two shields).
As such each operator would not actually be following their own light, they would just be adjusting their range settings so that they are looking at someone elses light through their sights.
As such the thing would operate like a ‘swarm’ rather than one coordinated machine.
Incidentally, the Roman galleys would be sitting ducks, the most they could do is shoot arrows at the defenders - and they would need a fair proportion of the crew manning the oars.
Not at all FRDE, slaves did the rowing
I don’t see why that would matter. If you’ve got 10,000 guys lined up around the harbor wall all aiming at one ship in general, who cares if 1, 10, or 500 of them are off somewhere. Even if the ship doesn’t actually catch fire, that’s gotta be incredibly distracting.
I rather doubt that
- Greek triremes, Roman Galleys etc were quite small
The Venetians did not use slaves (can’t cite - as intoxicated - ah, Dorothy Dunnet, some well researched fiction)
IMO slave galleys were useless for combat or invasion, a bit like Vikings using galley slaves - a waste of space.
Perhaps, but a besieged city has a finite supply of arrows and needs to think about where best to use them. Plus reflected light has longer range than an arrow. Plus you might have a bunch of guys unskilled in archery. Which isn’t to say it happened.
I think the problem is a little different than that. Given that the shields will be next to impossible to aim with any kind of super stability, what you’ll get with one shield is a spot of light that jiggles around. Maybe with the visual feebback that it’s your spot of light that’s moving, you could correct and keep it fairly tight. But now add another, and another, and another… Pretty soon you’re going to have a blob that jiggles all over the place in a sort of brownian motion. And since no one can tell which spot is theirs since it now all a uniform mash of light, you can’t correct your focus within the region. So it will grow until it gets to the size that represents all the shield-bearer’s respective abilities to aim without visual feedback.
At least, that’s how I perceive the problem.
Sam, that’s not how you aim a helioscope. Eah individual can aim his own, using any of a number of methods. But you certainly don’t look for your own personal spot on the target – that’s a recipe for disaster.
The easiest is to use a mirror that’s shiny front and back, with a hole drilled in the center. You look through the hole at your target, but you also see part of your face reflected in the shiny back surface. There will be a spot of sunlight on this, due to light passing through that hole. You adjust your mirror until the reflercted image of that spot gets lost in the aiming hole, or surrounds it, or whatever. Then you’re perfectly lined up.
There are other methods, such as using an aiming stick, and these were devweloped during the second World War to help downed airmen to aim their signalling mirrors (and presumably for anyone who had to use sun-signal-mirrors) and are outylined in an article in JOSA from 1945. As I mentioned, Hal Clement describes this method in his novel Cycle of Fire.
It’s true that everyone’s mirrors will keep moving around a bit, but on average, most will be pretty well centered, giving you a good time-averaged focus.
At least two books on Adaptive Optics (which use deformable mirrors that are automatically adjusted to do this) mention Archimedes as a sort of “patronm saint” of the craft (even though it was not Archimedes, but Proclus who was said to do this trick with men and shields.)
Agfain, I emphasize that, while I think this was certainly possible, I don’t think it probable. There are easier ways to destroy a ship than hoping for a really sunny day and getting a few hundred trained shieldmen who keep their shields nice and shiny just in case you can use this dodge.
Whatever literary crimes General Lew Wallace may have committed, his worst offense against knowledge was his insertion of the idea of a “Roman” galley slave into the novel Ben-Hur. The use of galley slaves, particularly on warships, does not appear to have been introduced to the Mediterranean until the around the 16th century C.E. (Changes in rowing technology may have have made slave galleys practicable by the fifth century C.E., but there is no record of such use for more than another millennium.)
Care to let us in on what this distinction betwen “mechanical” adjustment and “optical” adjustment might be? 
-FrL-
On the question of why one would do this, rather than use more conventional methods, you also have to consider the psychological aspect. Suppose you’re a Roman soldier, and the enemy shoots a fire arrow at your ship. Well, nobody likes being shot at, of course, but this is what you’ve trained for. You pour water on the arrow, or try to pull it out, or whatever the accepted standard countermeasure was at the time for fire arrows. What you don’t do is panic.
But now suppose that you’re that same soldier, and you see a bunch of enemy soldiers assembling on the hill above the beach. All of a sudden, you’re blinded by a brilliant flash of light covering the hillside, and next thing you know, your ship is burning, and you have no idea why or how. How do you suppose you’d react now? And if you happen to survive, and get back to the rest of your army and tell them about this, how do you suppose the rest of them will react?
I’m making a distinction between when you adjust the positions of mirrors or lenses by using mechanical readouts on the threads or using position gages, etc., coupled with calculations to get things into the correct position vs. aligning your optics by looking at multiple reflections, interference fringes, laser output, or other direct optical feedback about the operation of your device.
I know mechanical engineers take pride in accurate machining and positioning of parts, but, as an optical engineer who’s had to align devices to (extremely tight) optical tolerances, I’ve never seen a system that didn’t need such optical alignment to get it into the optimum functioning location. Maybe it’s error in calculation, or in machining, or tolerance buildup, but I’ve found that you can’t rely on your mechnical fixturing to get things properly aligned.
On MythBusters, they aligned those mirrors using mechanical positioning. And pretty crude mechanical positioning, at that – they set two directions of tilt using ordinary machine screw threads and a piece of aluminum cut into steps as a gauge. No way would that work. And they never checked it optically at intermediate points.
Here’s how to set it optically – use a laser, positioned horizontally, to strike at the center of each mirror segment, then adjust using your screws to get that reflected bgeam striking the center of where you want it to focus. (And don’t give me that “Archimedes couldn’t have done that!” There are other ways, such as using the sun as your source and covering all but one mirror segment at a time, and checking to see that your “axis” is pointed at the sun bwetween adjustments. But a laser is easier)
Diffraction from the mirror segments is going to be negligible – you ought to be able to get from each mirror segment a spot the size and shape of the projected mirror segment. They were using 6" or 12" pieces, so the “focal spot” should have been about that size, blurred a bit by the many edges being used. The spot actually was something like a yard across. I’m not surprised it didn’t work well.
Didn’t they do this on ‘What the Greeks did for us’? IIRC they set up mirrors and a model of a ship and the model did indeed catch fire.