Searching \ for '[OT]: 127 1 sq. ft. mirrors set a wooden boat on f' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=127+mirrors+set
Search entire site for: '127 1 sq. ft. mirrors set a wooden boat on f'.

Exact match. Not showing close matches.
PICList Thread
'[OT]: 127 1 sq. ft. mirrors set a wooden boat on f'
2005\10\23@220201 by Peter

picon face

Archimedes was not joking. Found via Slashdot. This seems to be a step
in the right direction wrt. (non)steam powered solar generation. 1100
deg. F is ~590 deg. C, ~860 K and ~2.6 bars of air pressure in 'my'
turbo system. 127 square feet of mirrors are ~11 square meters (11 kW in
the full sun). Their target (illuminated area) seems to be about 4-5
square feet (~0.5 sq. meters, from the photos) for a gain of ~25:1. I
think that they put about 5kW into that 0.5 sq. meter with losses.

I am surprised that such a high temperature could be reached in open air
(without a baffle or shield). I suppose that the charcoal formed a
porous surface that was both a blackbody and a shield against
convection. This is a good lesson ;-) Blackened (smoked) steel wool
looks good as 'blackbody' for the turbine experiments ;-)

http://web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html

Peter

2005\10\23@224723 by Tony Smith

picon face
>
> Archimedes was not joking. Found via Slashdot. This seems to be a step
> in the right direction wrt. (non)steam powered solar generation. 1100
> deg. F is ~590 deg. C, ~860 K and ~2.6 bars of air pressure in 'my'
> turbo system. 127 square feet of mirrors are ~11 square meters (11 kW in
> the full sun). Their target (illuminated area) seems to be about 4-5
> square feet (~0.5 sq. meters, from the photos) for a gain of ~25:1. I
> think that they put about 5kW into that 0.5 sq. meter with losses.
>
> I am surprised that such a high temperature could be reached in open air
> (without a baffle or shield). I suppose that the charcoal formed a
> porous surface that was both a blackbody and a shield against
> convection. This is a good lesson ;-) Blackened (smoked) steel wool
> looks good as 'blackbody' for the turbine experiments ;-)
>
> http://web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html


They did this because Mythbusters tried it, and couldn't get it to work.
The boat got a bit warm.

Slashdot has an update where Discovery Channel (produces Mythbusters)
invited MIT to have a go where they failed.

Didn't work.

No word on Round 3.

Tony

2005\10\24@051102 by Jinx

face picon face
> > web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html
>
> They did this because Mythbusters tried it, and couldn't
> get it to work. The boat got a bit warm.

So how does that affect Mythbusters' credibility ?

I'm sure if they'd actually tried cedar/wax instead of oak
it would've gone up a lot quicker, and probably with
fewer mirrors. I saw the builders next door putting cedar
scraps on their bonfire. Talk about flammable, went up
like cardboard. So although their experiment worked they
might have done it the hard way

> Slashdot has an update where Discovery Channel (produces
> Mythbusters) invited MIT to have a go where they failed.
>
> Didn't work.

But the class above is from MIT ?

2005\10\24@084632 by Denny Esterline

picon face
> > They did this because Mythbusters tried it, and couldn't
> > get it to work. The boat got a bit warm.
>
> So how does that affect Mythbusters' credibility ?
>

It doesn't, they didn't have any to start with :-)


Anybody whose seen steel melted with a solar furnace (~40 inch fresnel lens)
knows this is only a matter of focus. Wether Archimedies did it or not is a
question for historians to debate, but the possibility is evident to any
10-year old kid with a magnifing glass and an ant hill.

-Denny

2005\10\24@093426 by Wouter van Ooijen

face picon face
> So how does that affect Mythbusters' credibility ?

It busts their sense of logic. The fact that they could not reproduce
the effect does of course not prove that it is not possible, just that
it is not possible with the exact setup they used.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\10\24@103253 by Mike Hord

picon face
> > So how does that affect Mythbusters' credibility ?
>
> It busts their sense of logic. The fact that they could not reproduce
> the effect does of course not prove that it is not possible, just that
> it is not possible with the exact setup they used.

Ayup.  Let's not have another Mythbusters knock-down dragout,
okay?  It's just entertainment and NOT SCIENTIFIC.

After all, science is composed of things which can be conclusively
disproven, but can never be conclusively proven.

Mike H.

2005\10\24@110152 by Wouter van Ooijen
face picon face
> > It busts their sense of logic. The fact that they could not
> reproduce
> > the effect does of course not prove that it is not
> possible, just that
> > it is not possible with the exact setup they used.
>
> Ayup.  Let's not have another Mythbusters knock-down dragout,
> okay?  It's just entertainment and NOT SCIENTIFIC.

OK, read my post as "It busts *only* their sense of logic." and let me
add a belated smiley. :)

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\10\24@111925 by Tony Smith

picon face

{Quote hidden}

Mythbusters made a large disc, and covered it with mirrors.  Apparently that was how Archimedes did it.  They couldn't get the focus
tight enough.  From what I can remember, their model boat was made out of some sort of pine, then covered in tar, etc.

MIT lined up a bunch of mirrors in a row, and had to continually adjust them as the sun moved.  Got the boat to burn eventually.
Took 10 minutes.

The update is here:  http://science.slashdot.org/article.pl?sid=05/10/23/1349221&tid=14.  Bit light on details of what the second
MIT team did, but "mirrored system shaped like flower petals" sounds like what Mythbusters tried.

There was a bloke in the '70s who set a boat on fire with mirrors, so it's not like it can't be done.  Mythbusters' point was the
Archimedes story was a myth.  A big mirror makes a crap weapon, especially if you need to be in arrow range.

Don't forget http://www.solardeathray.com.

Tony

2005\10\24@142142 by Peter

picon face

On Mon, 24 Oct 2005, Tony Smith wrote:

> They did this because Mythbusters tried it, and couldn't get it to work.
> The boat got a bit warm.
>
> Slashdot has an update where Discovery Channel (produces Mythbusters)
> invited MIT to have a go where they failed.
>
> Didn't work.
>
> No word on Round 3.

About Mythbusters I don't really know or care. This is interesting to me
only from the point of view of its demonstration of the feasability of
high enough temperatures with simple mirrors in the sun, and without a
fancy receiver.

Peter

2005\10\24@161207 by David Van Horn

picon face

First surface mirrors would have worked a lot better.

Window glass passes near IR, but not far IR. So, those glass tiles
wouldn't have delivered nearly what a polished sheet of metal would.



2005\10\25@050329 by Russell McMahon

face
flavicon
face
> After all, science is composed of things which can be conclusively
> disproven, but can never be conclusively proven.

Naughty Mike!
Fancy bringing up religion again!!!
Such dangerous and heretical concepts must be nipped in the bud lest
they burst forth in a conflagration that will deluge the earth.
[Google knows].

Don't you know that such nasty biased assertions are banned on PICLIST
??? !
The cheek of, even ever so obliquely, hinting that there is "real
science" and 'hard science' versus various other sorts.
The utter nerve of bringing up the verboten issue of falsifiability.
You should be ashamed!

:-)

Keep up the good work.
Heresy will yet win the day.

Popper rulez !!!!!!


       R '3 cheers for hard Science' M



2005\10\25@115039 by Tony Smith

picon face
Only 3 problems with front surface mirrors - expensive, hard to get, and I don't think Archimedes had any.

Tony.

(flat front surface mirrors are used in kaleidoscopes, if anyone was wondering)


> {Original Message removed}

2005\10\25@122007 by Alan B. Pearce

face picon face
>Only 3 problems with front surface mirrors - expensive,
>hard to get, and I don't think Archimedes had any.

Oh, I dunno - polished metal sheet sounds very much like front surface
mirror to me ;)

2005\10\25@123958 by David Minkler

flavicon
face
The only mirrors Archimedes had were front surface (polished metal).  
Rear surface mirrors didn't appear until the 16th century (tin mercury
amalgam) and silver deposition wasn't invented until 1835.

Dave

Tony Smith wrote:

>Only 3 problems with front surface mirrors - expensive, hard to get, and I don't think Archimedes had any.
>
>Tony.
>
>(flat front surface mirrors are used in kaleidoscopes, if anyone was wondering)
>
>
>  
>
>>{Original Message removed}

2005\10\25@144125 by David Van Horn

picon face



Only 3 problems with front surface mirrors - expensive, hard to get, and I don't think Archimedes had any.


I don’t think he had any second surface mirrors.

-----Unmodified Original Message-----
Only 3 problems with front surface mirrors - expensive, hard to get, and I don't think Archimedes had any.

Tony.

(flat front surface mirrors are used in kaleidoscopes, if anyone was wondering)


> {Original Message removed}

2005\10\25@150822 by Peter

picon face


On Wed, 26 Oct 2005, Tony Smith wrote:

> Only 3 problems with front surface mirrors - expensive, hard to get,
> and I don't think Archimedes had any.

Make that two: he likely had ONLY front surface mirrors. Either bronze,
silver, or mercury polished copper.

Peter

2005\10\25@160315 by Bob Axtell

face picon face
Peter wrote:

> On Wed, 26 Oct 2005, Tony Smith wrote:
>
>> Only 3 problems with front surface mirrors - expensive, hard to get,
>> and I don't think Archimedes had any.
>
>
> Make that two: he likely had ONLY front surface mirrors. Either
> bronze, silver, or mercury polished copper.
>
> Peter

I believe the siege mirrors were polished bronze.

--Bob

--
Note: To protect our network,
attachments must be sent to
spam_OUTattachTakeThisOuTspamengineer.cotse.net .
1-520-777-7606 USA/Canada
http://beam.to/azengineer

2005\10\25@185229 by Denny Esterline

picon face
I realize the legend suggests the boats were set afire, but I was thinking
that might not be the most effective way to use a focused sunlight weapon.

Wood requires temperatures of several hundred degrees to ignite, and being
boats they would likely be wet (at least on the surface). But human flesh is
much more sensitive. Severe pain and injury could be achieved at
significantly lower temperatures than those needed to ignite wood. It seems
that even 3-4 times normal sunlight would be enough to cause eye injury or
at least temporary blindness, and would certainly be enough to prevent
attackers from effectively targeting the defending troops.

Thoughts?

-Denny

2005\10\25@193922 by Tony Smith

picon face
> I realize the legend suggests the boats were set afire, but I was thinking
> that might not be the most effective way to use a focused sunlight weapon.
>
> Wood requires temperatures of several hundred degrees to ignite, and being
> boats they would likely be wet (at least on the surface). But human flesh
> is
> much more sensitive. Severe pain and injury could be achieved at
> significantly lower temperatures than those needed to ignite wood. It
> seems
> that even 3-4 times normal sunlight would be enough to cause eye injury or
> at least temporary blindness, and would certainly be enough to prevent
> attackers from effectively targeting the defending troops.
>
> Thoughts?
>
> -Denny


Sounds ok, but hard to do in practice.  A scaled up version of kids frying
ants with a magnifying glass?

You need to focus on one person at a time, who'll be running around rather
quickly (or hiding).  Individual soldiers with polished shields wouldn't
be co-ordinated enough, it's hard to see your "hot spot" in amongst the
100 or so others.

A frame containing the mirrors is a bit large & heavy, so hard to swing
around easily.  Sure, you could hang it off some ropes, but then you also
need to adjust the focus.

I guess you could dazzle are few of them until their friends put a few
arrows in you.  The Romans always were sore losers.

Tony

2005\10\25@203851 by Jinx

face picon face
> Sounds ok, but hard to do in practice.  A scaled up version
> of kids frying ants with a magnifying glass ?

Oh, is THAT what they're doing. I always thought they were
just investigating the curious phenomenon of pismiral spontaneous
combustion ;-)

> You need to focus on one person at a time, who'll be running
> around rather quickly

You could always do the sails or ropes. Those old wooden ships
would have had easily-ignitable tar/wax/oil. Not forgetting that
the original ships were planked with cedar/cypress, which would
go up a lot quicker than oak

And no reason why some mirros couldn't be used to dazzle the
Roman's archers

==========================

I saw a documentary once in which they tried to re-construct
a full-sized Archimedes Claw

http://www.mlahanas.de/Greeks/Inventions.htm

"others they lifted up into the air by an iron hand or beak like a
crane's beak and, when they had drawn them up by the prow, and
set them on end upon the poop, they plunged them to the bottom of
the sea; or else the ships, drawn by engines within, and whirled
about, were dashed against steep rocks that stood jutting out under
the walls, with great destruction of the soldiers that were aboard
them. A ship was frequently lifted up to a great height in the air (a
dreadful thing to behold), and was rolled to and fro, and kept
swinging, until the mariners were all thrown out, when at length it
was dashed against the rocks, or let fall"

It worked (within limits), but outrageously heavy, cumbersome
and not very practical. Much more effective ways to attack a
ship in harbour

2005\10\25@212057 by Tony Smith

picon face
It took MIT 10 minutes to set fire to a boat just sitting there.  Maybe
you could ask them to drop anchor while you got organised.  Sounds like a
Monty Python sketch.  By that time the Romans would have swum ashore,
taken a few photos, grabbed some souvenirs and made a few large holes in
your body.

Tony

I saw that claw doco, can't say I was overly impressed.  If you're in claw
range, you might as well dump some burning oil or rocks on them.  I guess
you could throw bits of broken mirror at them too.

Tony




{Quote hidden}

> -

2005\10\25@222109 by Jinx

face picon face
> If you're in claw range, you might as well dump some
> burning oil or rocks on them.  I guess you could throw
> bits of broken mirror at them too

Then again, why can't we just all get along ? ;-))

2005\10\25@233521 by Tony Smith

picon face
>> If you're in claw range, you might as well dump some
>> burning oil or rocks on them.  I guess you could throw
>> bits of broken mirror at them too
>
> Then again, why can't we just all get along ? ;-))


Hey, the Romans started it!

Tony

2005\10\26@031505 by Russell McMahon

face
flavicon
face
> Only 3 problems with front surface mirrors - expensive, hard to get,
> and I don't think Archimedes had any.


I strongly suspect that front surface mirrors were the only sort that
Archimedes would have had available. What the that surface was made of
is another matter :-)



       RM

2005\10\26@150506 by Peter

picon face

On Wed, 26 Oct 2005, Jinx wrote:

> You could always do the sails or ropes. Those old wooden ships
> would have had easily-ignitable tar/wax/oil. Not forgetting that
> the original ships were planked with cedar/cypress, which would
> go up a lot quicker than oak

Nothing organic is 'easy to light' at 80-90% humidity as is often the
case around here, especially not something out on the water (even if
not in it).

Peter

2005\10\26@150800 by Peter

picon face

On Wed, 26 Oct 2005, Jinx wrote:

> Then again, why can't we just all get along ? ;-))

Guess how we can tell you live on a remote island (previously inhabited
by man-eaters ?) ? ;-)

Peter

More... (looser matching)
- Last day of these posts
- In 2005 , 2006 only
- Today
- New search...