Re: Odd query. Lenses-Optics in Antiquity
- From: Archer <champ@xxxxxxx>
- Date: Sun, 03 Feb 2008 13:30:15 -0000
On 2008-02-03, Matt Giwer <jull43@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
Archer wrote:
On 2008-02-02, Matt Giwer <jull43@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
Archer wrote:
On 2008-02-01, Matt Giwer <jull43@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
----snip----
The prototype is a four-foot square bronze plate. I'm resting it
on one corner on the ground. What "natural movement"?
The mechanism which allows it to be aimed being held by people as it
tracks the boat bobbing with the waves and maneuvering through the
water.
What mechanism?
Any mechanism which allows it the movement that is required to keep it
aimed at a moving boat in the distance. You have to have them people doing
the pointing moving it a small fraction of a degree vertically else it
cannot work at all. And it also has to track horizontal movement equally
accurately. It cannot be locked in place at any time.
Again. What mechanism?
There is no "mechanism" required. It's resting on a point on the ground.
The operator aims with the handles.
----snip----
BTW, it doesn't have to be four feet square. An elipse on a spike
would be more convenient to use.
It is the square footage that matters.
The point is that the shape can be anything convenient.
Do try to keep up.
and pray there is no
wind for the people trying to aim this 100 lb plate.
Oh, puhleez. A hoplite's full kit weighed less than that. There's
no need for a reflector to be anywhere near that heavy.
At 1000 feet with a vertical motion of 1 foot requires 1/10 degree
pointing accuracy and the ability to move it up and down 1/20 degree
accurately. While I disagree with your speculation on the weight
You're the one speculating about weight.
100 lb is absurd.
put a 100 lbs on your back and stand while not moving more than 1/20
degree. Hold 20 lbs for ten minutes and move no more than that.
Why? The ground is supporting the weight.
----snip----
BTW: The story
says shields, not flat at all.
Gee. I wonder what an ancient Greek word for a flat plate with handles
on one side would be?
I don't know but I do know there is no indication that their shields were
flat to better than one degree.
Duh. Essentially a shield was a metal plate with handles on one side.
Just like the reflectors I described, only not flat. You think the
ancients would have bothered to coin a word meaning "a thing like
a shield but flat"? Or bothered with a detailed description?
----snip----
Funny. The women used bronze mirrors. 'Tain't much of a leap.
Have you ever actually used a bronze mirror? I used to have a Chinese
one from the 19th century.
So a cheap replica is evidence against the possibility of a purpose-built
tool?
It was the real thing. I was into Chinese antiques in the good old days. It
was a functional mirror used by someone when it was new.
Nineteenth century Chinese is not antique. It was a replica of a design from
*real* antiquity. Mass produced tourist trash souvenirs, anyone?
----snip----
The man credited with this was considered an evil genius.
It is reported that just seeing him on the city walls was
sufficient to make the enemy uneasy. So there was an
accidental fire and the rumor mill accredited itto another
of his diabolical inventions.
Could be. I'm not saying that it was done, just that it was possible.
Which means you have seen the design requirements. To have a chance
against an boat on dry land at 1000 feet you have to get about 1/10
degree flatness.
Easy enough. Pour molten bronze into an oversized open-topped mould.
The surface is flat except at the edges (the meniscus).
Excuse me but we are talking about the usual shields being polished for
the purpose.
Wrong. That is *not* the basis of my contention that the feat was possible.
Cooling warps the surface.
You get a good start on flatness.
----snip----
Polish it with a straight edge.
You can't apply pressure and keep an edge straight over any distance.
AND you have to make it straight in the first place.
That's where the acuity of the hhuman eye comes in. You sight along it
and scrape, then polish, away the humps.
Also in the good
old days I was into lapidary and I never hears of a "straight edge"
polishing tool.
Probably has a technical term I don't know. Rotate a straight edge.
What have you got?
Oh, that's right. A flat disc.
----snip----
And where do you get "1000 feet"?
I use it as the shortest distance where starting fires on a single ship
might be practical.
LOL.
In practice without thousands of these magic mirrors
a fleet would have be "burned at 10,000 or more feet away. At 2 knots
which is very slow for rowing in those days 10,000 feet is a hour from
shore. 1000 feet is 12 minutes shore. That is a last chance fire
starting.
So you think the crew would be rowing, huh?
A good rowing team should have been able to do 6-7 kt. at
a minimum.
4-5 is a better estimate. Those ships weren't regatta hulls, and the crews
were the dregs of the slave market.
When I was a kid one inch lenses and the smallest spot possible barely
caused dry grass to smoke.
Funny. When I was a kid we started fires very easily that way.
Please describe your method.
Same as what you described.
Wet grass, wet as in a boat on water, was
not nearly as successful at starting a fire.
Not aiming at wet grass. Aiming at a wooden ship.
A wet wooden ship.
There are many dry flammables above the waterline and on deck,
including stores, rigging, bedding, the men's clothing, and the
captain's tent or cabin.
Who does anything become tinder dry at sea?
I presume that's a typo for "how".
Evaporation. Often wind-accelerated.
Clothing? Back then people
did not sweat in combat?
What combat? The ships are under way.
You think the soldiers, officers and engineers would be rowing?
You are going to have to be a lot more specific
if you are going to continue to pretend to be serious.
And if they came in under sail...
No one would try that in a harbor.
No-one would try that going into a seafight. IIRC, Syracuse's navy
had been disposed of.
And the men themselves are highly vulnerable to the heat.
Walk back and forth and laugh when the guys on the walls try to make
1/20 degree adjustments to follow you.
Tch. You display an appalling lack of imagination. Do try to imagine
1000 men aiming reflections of the sun at a ship. Not some particular
man on board: the ship is the target. Because of their height advantage
on the city walls, the beams are aimed down onto the deck. The beams
might be spread a little, and wander a little: the average temperature
increase divides over the total area they cover.
And guess what? The rowers can't escape it. The rigging, the deck,
and all the organic materials thereon can't be protected from it.
Now just how do all the
defenders pick out which man to target and why is he important?
Why do you make such an idiotic suggestion?
And to the light.
Only vampires last I heard.
Now *that* is a really stupid comment. Bright sunlight hurts some
people's eyes without *any* enhancement.
Assume a 10% efficiency: with a 300-man system, that magnifies the
heat and light by a factor of 30. You think that's nothing?
It wouldn't fire wood, but it would disable men instantly, and kill
them if their frantic scrambling about didn't get them overboard.
Why do you think I said "And there you have it: one 300-man death ray"?
With 1000 men, you get a magnification of 100 times.
BTW: Are you aware it was only about 20 years ago that military lasers
were powerful enough to do as you believe happened?
How many times do you have to be told?
I do NOT say (or believe) that it happened.
And then the absurdity of the story. Even if true, attack again at
night.
At last. A sensible objection.
Why'd it take you so long?
----
In fact, a smart man wouldn't do it at distance anyway. Your 1000 ft
would allow too many of the enemy to escape for a later attempt at
night or under cloud cover.
In fact, unless it was a sea attack against the walls, a smart man
wouldn't target ships under way at all. In that event though, he'd
wait for short range, attack the ships in the van to disorganize
them, then attack the ships at the rear to cut off the fleet's
escape, *then* aim for destruction.
But the thing to do with such a system would be attack the enemy's
siege engines. Those, if they moved at all, moved at a rate of feet
per day, and they can't be protected except by counterfire and
bucket brigades.
But we know that didn't happen, because the Romans won.
.
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- Re: Odd query. Lenses-Optics in Antiquity
- From: Matt Giwer
- Re: Odd query. Lenses-Optics in Antiquity
- From: Archer
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- From: Archer
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