On Mar 20, 5:52�pm, Dirk Bruere at NeoPax <dirk.bru...@gmail.com>
wrote:

> There is another possibility:http://www.ncbi.nlm.nih.gov/pubmed/17069982
> It may be that some people can detect magnetic North.
1) How useful would that really be in or near the Arctic Circle?
2) Why rely on a human senses when lodestones are so common?
Although I believe that some humans may have the ability to use
their nervous system for magnetic navigation, it would be in the
mariners interest to have a navigation tool which was not dependent on
the bodies physiological state. There were probably greatly skilled
individuals who could take all sorts of body cues to navigate.
The success of such a person would depend on his reputation. The
captain buying this persons services has to have some means of
verifying that the person really has the ability to tell true north. A
compass makes its capability quite obvious just by looking at it. A
device is always easier to sell than a reputation. A device doesn't
have a secret agenda. A person may.
Maybe the Vikings used lodestones for compass needles.
Lodestones would be fairly common Yet, I seldom here about the Vikings
having magnetic compasses. They use these sun stones, but not a
lodestone. No mention is made of the sun stones attracting iron, which
would be inevitable.
Maybe the Vikings used magnets. Maybe the association with the
sun is conjectural. Maybe the sun stones are really lodestones.
However, I doubt it. The magnetic field of the earth has a large
declination in that area. The magnetic field would be pointing
downward. The magnetic field would be highly biased horizontally by
all sorts of things. The horizontal magnetic field would be relatively
weak and so vulnerable to bias. I am not sure how reliably a compass.
The iron in the weapons would bias the compass. So they would have to
keep iron tools and weapons away from the compass.
Note, the magnetic human and the magnetic compass have the same
limitations. The human couldn't use his ability if he was holding a
sword, axe or hook. If he was wearing chain mail, forget it. The chain
mail would completely mess up magnetic navigation. The Vikings did not
use nails in their ships, so nails would not be a problem. However,
the navigator would have to be kept away from iron to use his magnetic
senses. Birds don't have these problems. So the fact that some people
have magnetic senses does not solve the problem of how the Vikings
navigated.
A magnetic compass would be of some use. There will be a tendency
to point to the magnetic north pole (somewhere in Canada?). Since
there are hot spots of magnetic activity, it may even have a use in
local navigation. However, I don't think a compass would be as
reliable as it would be in the lower latitudes.
I accept without reservation that there are certain cues that a
well experienced human being can used for navigation. I suppose that
for certain ventures, a navigation device wouldn't even be useful
given such skilled people. However, I am also sure that devices were
welcome so long as they were effective.
Fish have an interesting assortment of navigation senses. Sharks
use magnetic navigation. It has the interesting effect that they
circle certain islands with magnetic activity. I could see how a
magnetic navigator may be led to do similar things. Most bony fish use
olfactory cues. I think human beings probably use olfactory cures a
great deal when navigating. A lot of bony fish use solar navigation. I
suppose "dead reckoning" could include any number of these senses.

Darwin123 wrote:

> I accept without reservation that there are certain cues that a
> well experienced human being can used for navigation. I suppose that
> for certain ventures, a navigation device wouldn't even be useful
> given such skilled people. However, I am also sure that devices were
> welcome so long as they were effective.

Farley Mowat's 'West Viking' has an interesting argument about voyages from
Iceland to Greenland and on to Vinland. The land masses a visible for quite
a ways so the distances that require navigation are limited. You just need
to maintain your latitude, which is fairly easy with simple aids. The
problems come when a ship is blown off course. If you miss Greenland the
only option was to sail west until you found land and work your way up the
coast.

Darwin123 wrote:
>
> It seems to me that the stars, sun and moon would be much better
> than a magnetic compass. Or a magnetoreceptive human. That is not to
> say a magnetic compass couldn't be useful for certain purposes.

On an overcast day a calcite stone can be used to estimate the position
of the sun even though you can't tell just by looking at the sky.

On an overcast night a magnet can be used to estimate the direction for
north even though you can't tell just by looking at the sky.

In either case an objective estimate is better than a guess based on
hoping your sense of direction has not been lost.

> Hey, how close to the rotational pole was the magnetic pole in the
> year 1100 AD. The situation then isn't the same as it is now. The
> magnetic pole moves very slowly. In medieval times, would a magnetic
> compass be better or worse than it is now?

The magnetic pole wanders on a time scale of millennia.

On Mar 21, 8:43�pm, Dirk Bruere at NeoPax <dirk.bru...@gmail.com>
wrote:
> On 21/03/2011 15:18, Darwin123 wrote:
>
> > On Mar 20, 5:52 pm, Dirk Bruere at NeoPax<dirk.bru...@gmail.com>
> > wrote:
>
> >> There is another possibility:http://www.ncbi.nlm.nih.gov/pubmed/17069982
> >> It may be that some people can detect magnetic North.
> > 1) � How useful would that really be in or near the Arctic Circle?
>
> Not sure, but magnetic North wanders and does not (in the present day)
> line up with true North
That by itself is not a problem. If the magnetic field consistently
pointed to a certain spot on earth, it would be useful. If it changed
slowsly over a few hundred years, it would be useful to mariners.
Close to a magnetic pole, the magnetic field points
perpendicular to the surface. The horizontal component of the magnetic
field is quite small. Therefore, it could not be very useful for
navigation.
I was talking about the problem that when close to the pole, the
magnetic field does not consistently point toward a particular point
on the earths surface.
>
> > 2) Why rely on a human senses when lodestones are so common?
>
> The Vikings did not seem to know of them.
> Anyway, you don't even need lodestone.
> A thin piece of iron hammered on a N-S axis will become weakly
> magnetized. Hung from a piece of hair it should orient N-S
Okay, you hammered in my point.
They didn't even need lodestone or magnetoreception. They just
needed iron. There is no mention of hammered nails being used for
navigation.
A human had magnetoreception would not have an advantage over a
person with a hammered nail hung from a piece of hair.
That hammered nail would not orient strictly N-S near the magnetic
pole. It would not even be oriented hroizontally. It would point with
a certain declension downward. It may even point East-West relative to
the rotational pole of the earth. Suppose the nail pointed downward
with a slight tilt toward the East. Would that be useful to the
mariner?
It seems to me that the stars, sun and moon would be much better
than a magnetic compass. Or a magnetoreceptive human. That is not to
say a magnetic compass couldn't be useful for certain purposes.
They had lots and lots of calcite. So a sun stone may be useful
for orientation during those months the sun was below the horizon. The
problem is that during those months, the position of the sun could
still be estimated using the sky radiance. There may be slightly more
glow in the direction of the sun then else where. So the polarization
would only add a little more precision in that case.
Hey, how close to the rotational pole was the magnetic pole in the
year 1100 AD. The situation then isn't the same as it is now. The
magnetic pole moves very slowly. In medieval times, would a magnetic
compass be better or worse than it is now?
Right now, the magnetic pole is in Canada somewhere. Maybe it
was in Iceland. That would make a magnetic compass completely useless
in Iceland. Or maybe the two coincided better than they do now.
Are there any magnetic hot spots near Iceland? I mean, are there
any quadropoles or octopoles that open up near Norway? The earths
magnetic field is approximately dipolar, but not precisely. Further,
there is a lot of volcanic activity there. Igneous rock has "frozen"
magnetism in them.

On Mar 22, 11:17�am, robert bowman <bow...@montana.com> wrote:

> ...Iceland to Greenland and on to Vinland. The land masses a visible for quite
> a ways so the distances that require navigation are limited. You just need
> to maintain your latitude, which is fairly easy with simple aids.
Like a "sun stone"?
You just presented a good argument for these sun stones being
calcite crystals. If the Vikings were primarily interested in
maintaining their latitude heading, calcite crystals would be the way
to go.
The argument is whether those stories telling about "sun stones"
are really talking about calcite crystals. The calcite crystals would
be able to help the navigator determine the polarization of the
scattered light in the atmosphere, even when the sun was below the
horizon.
Polarized light light would not be able to distinguish longitude.
The Vikings didn't have anything like a marine chronometer, so there
was no way to determine longitude. In fact, I don't even think a
clacite crystal could be used to determine latitude. Thus, the
argument revolves around the use of a calcite crystal providing a
position at all. The polarization vector would not be uniquely
determined by the latitude.
The scattered light of the atmosphere is linearly polarized in
certain positions of the sky. The polarization vector in these sweet
spots would have a horizontal component pointing in the direction of
the latitude line. Therefore, it would be possible to MAINTAIN a
latitude heading using two calcite crystals.
Magnetic fields would not reliable for maintaining latitude.
Therefore, neither a magnetic compass nor a magnetoreceptive human
would be as useful for normal navigation as a pair of calcite
crystals.
The direction of the winds in summer may provide information on
the longitude. The direction of the wind would be repeatable during to
seasons of good weather. The wind direction would not be a precise or
reliable indicator of direction. However, you just gave an argument
that the land masses are visible for a large distance. So maybe one
didn't need a really good navigator for these regular trips. Calcite
crystals, wind direction and visible land masses would be together
pretty reliable for navigation between any two countries in northern
Europe.
Now, trips to the New World may have required a really good
navigator. No one knows how communities in Vinland maintained contact
with their European counterparts. Apparently, these colonies were not
isolated from Europe. People came and went between North America and
Europe. To navigate reliably between two points in different
hemispheres probably required every navigation trick the Vikings ever
had.

On Mar 31, 8:26�am, robert bowman <bow...@montana.com> wrote:

> Assuming a hull speed of 5 knots and a good wind, that's less than a day's
> sail. The jump from Greenland to Vinland is similar, and you have a much
> bigger target.
They had colonies. Colonies provide a much smaller cross section
than the continents that they are found.
The Vikings who lived in Greenland and Vinland had state visits
during weddings and such. They weren't just "continent hopping". They
knew precisely where they would end up.
Island hopping may be good if they just wanted to trade with
whoever they met. However, keeping up connections between ribes and
families would entail more precision in navigation.
Or it iss possible that they would hit the shore and start
following it to the colonies. If they did this is such an arbitrary
way, it would have taken more than a day.
No, I am not claiming to be an expert. I am just conjecturing. I
am seriously biased by the romantic notion that the Vikings knew where
they were going.
I don't know if they used calcite crystals for precise
navigation. However, they must have used something. Or a lot of things.

On 21/03/2011 15:18, Darwin123 wrote:
> On Mar 20, 5:52 pm, Dirk Bruere at NeoPax<dirk.bru...@gmail.com>
> wrote:
>
>> There is another possibility:http://www.ncbi.nlm.nih.gov/pubmed/17069982
>> It may be that some people can detect magnetic North.
> 1) How useful would that really be in or near the Arctic Circle?

Not sure, but magnetic North wanders and does not (in the present day)
line up with true North

> 2) Why rely on a human senses when lodestones are so common?

The Vikings did not seem to know of them.
Anyway, you don't even need lodestone.
A thin piece of iron hammered on a N-S axis will become weakly
magnetized. Hung from a piece of hair it should orient N-S

> Although I believe that some humans may have the ability to use
> their nervous system for magnetic navigation, it would be in the
> mariners interest to have a navigation tool which was not dependent on
> the bodies physiological state. There were probably greatly skilled
> individuals who could take all sorts of body cues to navigate.
> The success of such a person would depend on his reputation. The
> captain buying this persons services has to have some means of
> verifying that the person really has the ability to tell true north. A
> compass makes its capability quite obvious just by looking at it. A
> device is always easier to sell than a reputation. A device doesn't
> have a secret agenda. A person may.
> Maybe the Vikings used lodestones for compass needles.
> Lodestones would be fairly common Yet, I seldom here about the Vikings
> having magnetic compasses. They use these sun stones, but not a
> lodestone. No mention is made of the sun stones attracting iron, which
> would be inevitable.
> Maybe the Vikings used magnets. Maybe the association with the
> sun is conjectural. Maybe the sun stones are really lodestones.
> However, I doubt it. The magnetic field of the earth has a large
> declination in that area. The magnetic field would be pointing
> downward. The magnetic field would be highly biased horizontally by
> all sorts of things. The horizontal magnetic field would be relatively
> weak and so vulnerable to bias. I am not sure how reliably a compass.
> The iron in the weapons would bias the compass. So they would have to
> keep iron tools and weapons away from the compass.
> Note, the magnetic human and the magnetic compass have the same
> limitations. The human couldn't use his ability if he was holding a
> sword, axe or hook. If he was wearing chain mail, forget it. The chain
> mail would completely mess up magnetic navigation. The Vikings did not
> use nails in their ships, so nails would not be a problem. However,
> the navigator would have to be kept away from iron to use his magnetic
> senses. Birds don't have these problems. So the fact that some people
> have magnetic senses does not solve the problem of how the Vikings
> navigated.
> A magnetic compass would be of some use. There will be a tendency
> to point to the magnetic north pole (somewhere in Canada?). Since
> there are hot spots of magnetic activity, it may even have a use in
> local navigation. However, I don't think a compass would be as
> reliable as it would be in the lower latitudes.
> I accept without reservation that there are certain cues that a
> well experienced human being can used for navigation. I suppose that
> for certain ventures, a navigation device wouldn't even be useful
> given such skilled people. However, I am also sure that devices were
> welcome so long as they were effective.
> Fish have an interesting assortment of navigation senses. Sharks
> use magnetic navigation. It has the interesting effect that they
> circle certain islands with magnetic activity. I could see how a
> magnetic navigator may be led to do similar things. Most bony fish use
> olfactory cues. I think human beings probably use olfactory cures a
> great deal when navigating. A lot of bony fish use solar navigation. I
> suppose "dead reckoning" could include any number of these senses.
>

--
Dirk

http://www.neopax.com/technomage/ - My new book - Magick and Technology

On Mar 25, 10:53�am, robert bowman <bow...@montana.com> wrote:
> Darwin123 wrote:
> > Like a "sun stone"?
> > You just presented a good argument for these sun stones being
> > calcite crystals. If the Vikings were primarily interested in
> > maintaining their latitude heading, calcite crystals would be the way
> > to go.
>
> Actually, no. I was talking about the simple measurement of the angle of the
> sun or North Star.

You are right. The North Star could be as good as good as any Sun
Stone at night. However, ships have to sail night and day.
Maybe the North Star was used at "night" (where the sun is
lowest) and the sun stone during the "day" (where the sun is
highest). Near the Artice circle, the sun is below the the horizon
for months at a time. However, there would be periods in the diurnal
cycle where the scattered light from the sun would be so bright that
the stars couldn't be clearly seen.
Above the Arctic circle but not at the North pole, the sun
would be above the horizon half the year and below the horizon half
the year. Yet, the apparent path of the sun would still be tilted with
respect to the horizon, even in the months where the sun is below the
horizon. In the months that the the sun is below the horizon, Polaris
would still be visible only part time even in clear weather. The image
of the sun would never be visible during those months. If the sun is
close to the horizon, the scattered light will be bright enough to
obscure Polaris. So even if the image of the sun is invisible, it is
bright enough to interfere with stellar navigation.
The calcite crystals could be useful to determine North during
those times. Although the position of the sun is invisible at such
times, the polarization of the scattered light could provide an
estimate of where the image of the sun "should be." Every 12 hours the
sun sinks sufficiently below the horizon for Polaris to show itself.
However, Polaris still would only be visible for a few hours of the
diurnal cycle.

On Apr 8, 11:53�am, clifford wright <c.c.wri...@paradise.net.nz>
wrote:
> Darwin123 <drosen0...@yahoo.com> wrote innews:a778184f-f742-4f30-9439-6b465ff24aa1@s9g2000yqm.googlegroups.com:
>
>
>
> > On Mar 31, 8:26 am, robert bowman <bow...@montana.com> wrote:
>
> >> Assuming a hull speed of 5 knots and a good wind, that's less than a
> >> day's sail. The jump from Greenland to Vinland is similar, and you
> >> have a much bigger target.
> > � �They had colonies. Colonies provide a much smaller cross section
> > than the continents that they are found.
> > � � �The Vikings who lived in Greenland and Vinland had state visits
> > during weddings and such. They weren't just "continent hopping". They
> > knew precisely where they would end up.
> > � �Island hopping may be good if they just wanted to trade with
> > whoever they met. However, keeping up connections between ribes and
> > families would entail more precision in navigation.
> > � � � Or it iss possible that they would hit the shore and start
> > following it to the colonies. If they did this is such an arbitrary
> > way, it would have taken more than a day.
> > � � �No, I am not claiming to be an expert. I am just conjecturing. I
> > am seriously biased by the romantic notion that the Vikings knew where
> > they were going.
> > � � �I don't know if they used calcite crystals for precise
> > navigation. However, they must have used something. Or a lot of
> > things.
>
> Well I'm Asatru and an amateur astronomer. I have a lump of "sunstone"
> (Iceland spar) and while it isn't accurate it greatly improves a
> navigators "best guess" of the Sun's altitude in overcast conditions.
> As other posters have mentioned, the effect seems to be due to its use as
> a polarising filter. It would certainly improve a navigators estimate of
> latitude.
That is all that I have been saying.

On Mar 30, 10:57�am, robert bowman <bow...@montana.com> wrote:

> Near the Circle, sane Vikings would be hanging around a nice warm fire
> someplace not trying to kill themselves in the dark winter storms.
You are right. However, the trips were usually chosen by the
direction of the winds rather than the temperature. Sailboats depend
on wind. For very long trips, they may not have had much choice. Part
of the trip may have had to start while it was still dark.
The ones that travel on really long trips, like to Vinland,
may not have stuck to the schedule other Vikings used. Some of the
trips may have started in the late winter, or ended in the early
winter. By the time they got to Vinland, it would be much warmer.
Some of the sagas where sun stones are used may have referred to the
long trip between continents. It depends on where the winds and ocean
currents are pointing. This wasn't a trip of a few days.
You seem to be implying that the calcite crystals had no real use
in navigation. If so, you are very likely to be right. I am taking an
unlikely conjecture to its most extreme. Probably the Vikings stayed
home in the dead winter. This implies that they probably did not have
any use for calcite crystals as a navigation tool.
The sun stones (calcite crystals) would be very useful only
under the following conditions. Clear skies. Sky radiance bright
enough to mask the position of the stars. A sun that is just below the
horizon. If those conditions are met, I think a sun stone would be at
least as desirable as a magnetic compass.
1) So why didn't Vikings use magnetic compasses on the really long
trips?
2) Why don't we have sagas talking about a magnetic compass?
3) Why can't the sun stones be a magnetic compass?

Darwin123 wrote:

> 1) So why didn't Vikings use magnetic compasses on the really long
> trips?
> 2) Why don't we have sagas talking about a magnetic compass?
> 3) Why can't the sun stones be a magnetic compass?

You have to ask yourself what the really long trips would be. Much of the
travel would be coasting. Some of the longer voyages would have been done
by island hopping, the Orkneys and Faroes for example. The point Mowat
makes is for the Iceland to Greenland run, the heads on Iceland are visible
astern for a long way, and the heads on Greenland stand out also. iirc,
there is only about 100 miles where you can't see one or the other.
Assuming a hull speed of 5 knots and a good wind, that's less than a day's
sail. The jump from Greenland to Vinland is similar, and you have a much
bigger target. Sail west by the sun and stars until you hit land and then
coast.

Other than storms, the real danger is fog. My sailing was done before GPS's,
and even people with LORAN were not enthused by fog, especially on the
coast of Maine. It's rocky with many small islands, not a good place to not
know exactly where you are and to not be able to see more than yards ahead.
It's especially harrowing if you hear waves breaking and can't really
determine what direction the sound is coming from.

Darwin123 <drosen0000@yahoo.com> wrote in
news:a778184f-f742-4f30-9439-6b465ff24aa1@s9g2000yqm.googlegroups.com:

> On Mar 31, 8:26�am, robert bowman <bow...@montana.com> wrote:
>
>> Assuming a hull speed of 5 knots and a good wind, that's less than a
>> day's sail. The jump from Greenland to Vinland is similar, and you
>> have a much bigger target.
> They had colonies. Colonies provide a much smaller cross section
> than the continents that they are found.
> The Vikings who lived in Greenland and Vinland had state visits
> during weddings and such. They weren't just "continent hopping". They
> knew precisely where they would end up.
> Island hopping may be good if they just wanted to trade with
> whoever they met. However, keeping up connections between ribes and
> families would entail more precision in navigation.
> Or it iss possible that they would hit the shore and start
> following it to the colonies. If they did this is such an arbitrary
> way, it would have taken more than a day.
> No, I am not claiming to be an expert. I am just conjecturing. I
> am seriously biased by the romantic notion that the Vikings knew where
> they were going.
> I don't know if they used calcite crystals for precise
> navigation. However, they must have used something. Or a lot of
> things.
>
>

Well I'm Asatru and an amateur astronomer. I have a lump of "sunstone"
(Iceland spar) and while it isn't accurate it greatly improves a
navigators "best guess" of the Sun's altitude in overcast conditions.
As other posters have mentioned, the effect seems to be due to its use as
a polarising filter. It would certainly improve a navigators estimate of
latitude.
In fact I'm into reenactment of many historical periods from the
technical and scientific point of view. I must be about the only "Ham' in
New zealand with a working spark trasmitter and a set of 10th century
armour!
Cliff Wright ZL1BDA New Zealand.

Darwin123 wrote:
> Doug Freyburger <dfrey...@yahoo.com> wrote:
>
>> On an overcast day a calcite stone can be used to estimate the position
>> of the sun even though you can't tell just by looking at the sky.

Estimation method one.

> Thank you. I didn't realize that a calcite stone could work on an
> overcast day. I think that you are right.
>
>> On an overcast night a magnet can be used to estimate the direction for
>> north even though you can't tell just by looking at the sky.

Estimation method two.

> Then why not use the same magnet during the day?
> If you have a magnet, you don't need a calcite stone as much. On
> the other hand, the calcite stone may be more accurate than the magnet
> under certain conditions.

When you have more than one estimation method, use them and average the
results. You get a better answer than if you only used one of them.
Both beats either/or.

http://www.newscientist.com/article/dn20052-vikings-crystal-clear-method-of-navigation.html

Viking sagas may have been more truthful than we realised. Crystal
"sunstones" could have helped Viking sailors to navigate even when cloud
or fog hid the sun.

Vikings navigated using sundials calibrated to show the direction of the
North Pole. While there is no physical evidence for the navigational
techniques adopted on cloudy days, there are references in the Viking
sagas to "sunstones" being used.

In 1967, Danish archaeologist Thorkild Ramskou suggested that sunstones
may work by creating a pattern of light that revealed the hidden sun's
location – although sceptics countered that the method is unwieldy, if
not unworkable.

It is only within the last 10 years that Ramskou's theory has been put
to the test, and the results, summarised in Philosophical Transactions
of the Royal Society B (DOI: 10.1098/rstb.2010.0194), claim to
demonstrate that the sunstone method does work in cloudy or foggy
conditions.

Sunstones – translucent crystals of minerals such as calcite – are
potentially useful because both they, and the atmosphere, behave like
natural Polaroid filters. This means they polarise light, causing its
photons to vibrate in only one plane. Crucially for this navigation
technique, the atmosphere leaves sunlight polarised in a series of
concentric rings centred on the sun.
Pinpoint the sun

It is this pattern that can be detected using a sunstone – at least in
theory. When the crystal is pointed skywards and rotated, the theory
goes, the light passing through it progressively brightens and dims,
depending on whether the crystal's direction of polarisation is aligned
or misaligned with the polarisation rings in the atmosphere. When the
two are aligned, the crystal appears at its brightest and points towards
the sun – even if the sun is hidden. Taking two readings at different
points in the sky should enable a navigator to pinpoint the sun's position.

Once the position of the sun was established, Ramskou speculated, Viking
navigators could hold a lighted torch in the correct position above
their sundial, giving them the required shadow reading on the dial.

However, critics say that too little polarised light passes through
clouds to take accurate readings using a sunstone. So to settle the
dispute, Gábor Horváth at Eötvös University in Budapest, Hungary, and
colleagues studied polarisation patterns under cloudy skies and foggy
conditions in Hungary, Finland and within the Arctic circle.

Using a polarimeter, which determines light's angle of polarity,
Horváth's team found that the atmospheric polarity patterns can be
detected even under cloudy skies or foggy conditions, suggesting that
the Vikings could have made use of them. The patterns are difficult to
detect under completely overcast conditions, however.

Despite the latest evidence, not everyone is convinced. "The sky is
strongly polarised only in certain regions relative to the sun," says
Tom Cronin of the University of Maryland, Baltimore, and an authority on
polarisation. "If the light's not very polarised, the sunstone won't get
[bright or] dark enough [when rotated]," he says. "So I think it would
work, but not very accurately."

Also, Horváth and his team have yet to demonstrate that real sunstones –
crystals mined in Scandinavia or Iceland – could detect the weak
patterns under cloudy skies as well as their sensitive polarimeter can,
which is something he is now investigating. If they do, Horváth will
have compelling evidence that the Vikings possessed both the ways and
the means to navigate under cloudy skies.
_________

--
FFF
Dirk

http://www.neopax.com/technomage/ - My new book - Magick and Technology

On Feb 1, 12:38�am, Dirk Bruere at NeoPax <dirk.bru...@gmail.com>
wrote:

> Despite the latest evidence, not everyone is convinced. "The sky is
> strongly polarised only in certain regions relative to the sun," says
> Tom Cronin of the University of Maryland, Baltimore, and an authority on
> polarisation. "If the light's not very polarised, the sunstone won't get
> [bright or] dark enough [when rotated]," he says. "So I think it would
> work, but not very accurately."
I read that too. I have heard that an "expert" seaman can dead-
reckon far more accurately than these stones could indicate. This
seems reasonable to me, being an optical physicists. Polarized light
from sky radiance would not be very accurate. Calcite would only work
when the weather was perfect, and would be good for only a few degree
accuracy. It would be accurate even when the sun were below the
horizon. Above the Arctic circle, this would be a marginal advantage.
However, there are several methods under the heading of dead reckoning
that would work at night.
Except, my experience as a physics "expert" suggests the
following. I think the magic stones would still be useful.
I don't think a real "expert" in anything wants to rely on one
method of determining something important. I was always using "sanity
tests" when I designed something.
I think a good mariner would welcome a "sanity test" even if he
had incredible dead reckoning skills. A person who dead reckons would
have to pay attention and concentrate very hard over a very long
period of time.
"Dead reckoning" takes a lot of variables into account. It would
not be really shameful for a navigator to want to recheck his bearing.
Especially while he is recovering from a stab wound. Or from a really
powerful blow on the head.
Or if the expert navigator got killed. Suppose you had a Viking
ship full of 12 muscle men and 3 specialized navigators. I assume that
the 12 muscle men all have navigation skills suitable for near shore
navigation, but the deep sea navigation is the provinence of the
specialists. After a big battle, you have 4 muscle men and no
navigators.
Don't you think the survivors would be satisfied with an
"inaccurate" calcite crystal? Or even if they thought their navigation
skills were adequate, that they wouldn't want some confirmation?
The magic stones (i.e., calcite) could have been like emergency
equipment. Or like a security blanket.
If I were a navigation expert, I would check each of my determined
locations in as many ways as I could. I might even assign a less
skilled member of the crew to do an independent check using "magic
stones." Even if I was damn sure about my dead reckoning skills, I
would want the rest of the crew to trust me. If they could check my oh
so mariner skills, I would want to show them how great they are just
so no one is tempted to mutiny. So I would encourage the rest of the
crew to use "magic stones."
A device that gave a ball park approximation only under great
weather conditions would still be useful. Because if the "experts"
concentration were distracted for any trivial reason (like pirate
attack, sickness, injury, volcanic eruption), he would want
reassurance that he hadn't lost track completely.
When I figure out something important, I like to figure it out at
least three different ways. This way, if I make a mistake, it is more
likely to show up.
So maybe the "magic stones" were really a sanity test for the
mariner. He had lots of ways to determine his position, but it was
nice to have at least one that couldn't be effected by my
physiological state.

On 18/03/2011 15:42, Darwin123 wrote:
> On Feb 1, 12:38 am, Dirk Bruere at NeoPax<dirk.bru...@gmail.com>
> wrote:
>
>> Despite the latest evidence, not everyone is convinced. "The sky is
>> strongly polarised only in certain regions relative to the sun," says
>> Tom Cronin of the University of Maryland, Baltimore, and an authority on
>> polarisation. "If the light's not very polarised, the sunstone won't get
>> [bright or] dark enough [when rotated]," he says. "So I think it would
>> work, but not very accurately."
> I read that too. I have heard that an "expert" seaman can dead-
> reckon far more accurately than these stones could indicate. This
> seems reasonable to me, being an optical physicists. Polarized light
> from sky radiance would not be very accurate. Calcite would only work
> when the weather was perfect, and would be good for only a few degree
> accuracy. It would be accurate even when the sun were below the
> horizon. Above the Arctic circle, this would be a marginal advantage.
> However, there are several methods under the heading of dead reckoning
> that would work at night.
> Except, my experience as a physics "expert" suggests the
> following. I think the magic stones would still be useful.
> I don't think a real "expert" in anything wants to rely on one
> method of determining something important. I was always using "sanity
> tests" when I designed something.
> I think a good mariner would welcome a "sanity test" even if he
> had incredible dead reckoning skills. A person who dead reckons would
> have to pay attention and concentrate very hard over a very long
> period of time.
> "Dead reckoning" takes a lot of variables into account. It would
> not be really shameful for a navigator to want to recheck his bearing.
> Especially while he is recovering from a stab wound. Or from a really
> powerful blow on the head.
> Or if the expert navigator got killed. Suppose you had a Viking
> ship full of 12 muscle men and 3 specialized navigators. I assume that
> the 12 muscle men all have navigation skills suitable for near shore
> navigation, but the deep sea navigation is the provinence of the
> specialists. After a big battle, you have 4 muscle men and no
> navigators.
> Don't you think the survivors would be satisfied with an
> "inaccurate" calcite crystal? Or even if they thought their navigation
> skills were adequate, that they wouldn't want some confirmation?
> The magic stones (i.e., calcite) could have been like emergency
> equipment. Or like a security blanket.
> If I were a navigation expert, I would check each of my determined
> locations in as many ways as I could. I might even assign a less
> skilled member of the crew to do an independent check using "magic
> stones." Even if I was damn sure about my dead reckoning skills, I
> would want the rest of the crew to trust me. If they could check my oh
> so mariner skills, I would want to show them how great they are just
> so no one is tempted to mutiny. So I would encourage the rest of the
> crew to use "magic stones."
> A device that gave a ball park approximation only under great
> weather conditions would still be useful. Because if the "experts"
> concentration were distracted for any trivial reason (like pirate
> attack, sickness, injury, volcanic eruption), he would want
> reassurance that he hadn't lost track completely.
> When I figure out something important, I like to figure it out at
> least three different ways. This way, if I make a mistake, it is more
> likely to show up.
> So maybe the "magic stones" were really a sanity test for the
> mariner. He had lots of ways to determine his position, but it was
> nice to have at least one that couldn't be effected by my
> physiological state.
>

There is another possibility:
http://www.ncbi.nlm.nih.gov/pubmed/17069982
It may be that some people can detect magnetic North.

--
FFF
Dirk

http://www.neopax.com/technomage/ - My new book - Magick and Technology

Darwin123 wrote:

> Near the Artice circle, the sun is below the the horizon
> for months at a time. However, there would be periods in the diurnal
> cycle where the scattered light from the sun would be so bright that
> the stars couldn't be clearly seen.

Near the Circle, sane Vikings would be hanging around a nice warm fire
someplace not trying to kill themselves in the dark winter storms.

On Mar 24, 12:00�pm, Doug Freyburger <dfrey...@yahoo.com> wrote:
> Darwin123 wrote:
>
> > � � �It seems to me that the stars, sun and moon would be much better
> > than a magnetic compass. Or a magnetoreceptive human. That is not to
> > say a magnetic compass couldn't be useful for certain purposes.
>
> On an overcast day a calcite stone can be used to estimate the position
> of the sun even though you can't tell just by looking at the sky.
Thank you. I didn't realize that a calcite stone could work on an
overcast day. I think that you are right.
>
> On an overcast night a magnet can be used to estimate the direction for
> north even though you can't tell just by looking at the sky.
Then why not use the same magnet during the day?
If you have a magnet, you don't need a calcite stone as much. On
the other hand, the calcite stone may be more accurate than the magnet
under certain conditions.