Hello,


I have 2 magnetic compasses, one of which for some mysterious reason has
reversed polarity ie. red points south!!!!

Pic he http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?


D

Vortex3 wrote:
Hello,


I have 2 magnetic compasses, one of which for some mysterious reason has
reversed polarity ie. red points south!!!!

Pic he http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?


Oh yes.

Its dead easy.

Put compass in BIG hollow solenoid. Wind this out of almost anything
wire shaped round a bot of drainpipe or wate pi[e depending on gow big
it is.

Get car battery, and some 30 amp fuse wire. Make fuse in one bit of
wire. Connect one end to battery and then apply other to other pole of
battery. Fuse will blow, but not before compass is well and truly
remagnetised. If it doesn't work, align the pipe in reverse direction
and try again.

Be wary if your compass has correcting magnets. They will get remagged
as well.



D

Vortex3 formulated on Friday :
Hello,


I have 2 magnetic compasses, one of which for some mysterious reason has
reversed polarity ie. red points south!!!!

Pic he http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?

My best guess would be that it has been sat for a long time with the
needle pointing in the wrong direction, with the case tilted just
enough to prevent the needle swinging and the earths field has managed
to remagnetise it with the wrong polarity.

You need to tilt it enough to again jam the needle and then stroke the
end of a strong magnet along the full length of the needle. It needs
the strokes to be done in one direction - lift the magnet at the end of
each stroke well away, then start fresh stroke. It might need some
practise not to get the magnet so close that it makes the needle move.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Invisible Man wrote:
Vortex3 wrote:
Hello,


I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!

Pic he http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?

D

Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.

The correct direction is the one that works ;-)

On 6 Feb, 18:02, "Vortex3" wrote:

Can anybody suggest a non-destructive method to correct this?

Buy a new compass. The power needed to re-magnetise it reliably from
outside the sealed vial is going to be considerably more than that
needed to do a bare needle - I suspect impractically so.

What you need is a big hollow solenoid coil (lots of windings on a
tube) and then a crude capacitor discharge system to put one hell of a
wallop through that coil. As the coil is inductive, it's actually
quite hard to do this! Big paper capacitors and a big old Dr
Frankenstein knife switch are the usual way.

You're unlikely to do it with a battery, as you won't get enough
current. You _might_ be able to do it with something like a short-
circuited destructive use of a battery, if you have a crate of old
laptops to dispose of... 8-)

"Andy Dingley" wrote in message
...
On 6 Feb, 18:02, "Vortex3" wrote:

Can anybody suggest a non-destructive method to correct this?

Buy a new compass. The power needed to re-magnetise it reliably from
outside the sealed vial is going to be considerably more than that
needed to do a bare needle - I suspect impractically so.

What you need is a big hollow solenoid coil (lots of windings on a
tube) and then a crude capacitor discharge system to put one hell of a
wallop through that coil. As the coil is inductive, it's actually
quite hard to do this! Big paper capacitors and a big old Dr
Frankenstein knife switch are the usual way.

You're unlikely to do it with a battery, as you won't get enough
current.



How much current are you figuring on needing then ? The average car battery
is good for at least 200 amps, and more if it's a big 'un ...

Arfa

On Feb 7, 7:02 am, "Vortex3" wrote:
Hello,

I have 2 magnetic compasses, one of which for some mysterious reason has
reversed polarity ie. red points south!!!!

Congratulations for noticing this before going out into the wilds.
I had a similar compass with that problem. I fixed it by tilting it so
the needle didn't move then waved a powerful magnet at it, which is
probably how it got wrong in the first place.

Can anybody suggest a non-destructive method to correct this?

My best guess would be that it has been sat for a long time with the
needle pointing in the wrong direction, with the case tilted just enough
to prevent the needle swinging and the earths field has managed to
remagnetise it with the wrong polarity.

You need to tilt it enough to again jam the needle and then stroke the end
of a strong magnet along the full length of the needle. It needs the
strokes to be done in one direction - lift the magnet at the end of each
stroke well away, then start fresh stroke. It might need some practise not
to get the magnet so close that it makes the needle move.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk



Cheers Harry,

I will try this approach first!

I am told hard disk heads contain very powerful "rare earth" magnets. Since
I have an old crashed disk here I will begin by extracting its magnets later

D

On Feb 7, 12:06*am, Jason wrote:
Invisible Man wrote:
Vortex3 wrote:
Hello,

I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!

Pic he * * * * *http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. *I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?

D

Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.

The correct direction is the one that works ;-)

This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Arfa Daily wrote:
"Andy Dingley" wrote in message
...
On 6 Feb, 18:02, "Vortex3" wrote:

Can anybody suggest a non-destructive method to correct this?
Buy a new compass. The power needed to re-magnetise it reliably from
outside the sealed vial is going to be considerably more than that
needed to do a bare needle - I suspect impractically so.

What you need is a big hollow solenoid coil (lots of windings on a
tube) and then a crude capacitor discharge system to put one hell of a
wallop through that coil. As the coil is inductive, it's actually
quite hard to do this! Big paper capacitors and a big old Dr
Frankenstein knife switch are the usual way.

You're unlikely to do it with a battery, as you won't get enough
current.



How much current are you figuring on needing then ? The average car battery
is good for at least 200 amps, and more if it's a big 'un ...


Exacltly and in fact we did this at achool with a big solenoid and AC.
Its random as to which way it goes though.

Or put near a CRT TV and let the degaussers hit it when you switch it on..

A car battery and a fuse is what will supply the ommph. Magnetic field
in the middle is ampere turns, so its not the amps alone. Have more
turns. Just make the fuse go before the wire comprising the solenoid ...

The inducance of it will mean te current build up wuite loswly, reaches
a peak, and then the fuse goes. It works.

Probably a 50 meters of single core bell wire would do the trick round a
drainpipe.


Arfa

"Vortex3" wrote in message
...


Can anybody suggest a non-destructive method to correct this?

My best guess would be that it has been sat for a long time with the
needle pointing in the wrong direction, with the case tilted just enough
to prevent the needle swinging and the earths field has managed to
remagnetise it with the wrong polarity.

You need to tilt it enough to again jam the needle and then stroke the
end of a strong magnet along the full length of the needle. It needs the
strokes to be done in one direction - lift the magnet at the end of each
stroke well away, then start fresh stroke. It might need some practise
not to get the magnet so close that it makes the needle move.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk



Cheers Harry,

I will try this approach first!

I am told hard disk heads contain very powerful "rare earth" magnets.
Since I have an old crashed disk here I will begin by extracting its
magnets later


I'm not so sure about hard disks having strong magnets in them. The head is
a strong electromagnet but it only over a very small area!

If I wanted a strong magnet I'd aim for a magnetron in a microwave.

Fred wrote:
"Vortex3" wrote in message
...

Can anybody suggest a non-destructive method to correct this?
My best guess would be that it has been sat for a long time with the
needle pointing in the wrong direction, with the case tilted just enough
to prevent the needle swinging and the earths field has managed to
remagnetise it with the wrong polarity.

You need to tilt it enough to again jam the needle and then stroke the
end of a strong magnet along the full length of the needle. It needs the
strokes to be done in one direction - lift the magnet at the end of each
stroke well away, then start fresh stroke. It might need some practise
not to get the magnet so close that it makes the needle move.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


Cheers Harry,

I will try this approach first!

I am told hard disk heads contain very powerful "rare earth" magnets.
Since I have an old crashed disk here I will begin by extracting its
magnets later


I'm not so sure about hard disks having strong magnets in them. The head is
a strong electromagnet but it only over a very small area!

If I wanted a strong magnet I'd aim for a magnetron in a microwave.


The motor that positions the head is based on a strong magnet. In my
experience, fairly easy to open up and remove (might require a Torx driver).

Suggest you only do this to redundant drives as re-assembly is not the
reverse of dis-assembly. (Haynes passim.) :-)

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

Rod wrote:

The motor that positions the head is based on a strong magnet. In my
experience, fairly easy to open up and remove (might require a Torx
driver).

Those things are strong, and pinch flesh badly if mishandled.

Is there a legal maximum you are allowed to have in ownership least you
accidently down planes, attract trains and dismantle automobiles?

--
Adrian C

Adrian C wrote:

Is there a legal maximum you are allowed to have in ownership least you
accidently down planes, attract trains and dismantle automobiles?

http://www.supermagnete.de/eng/more_...d=Q-51-51-25-N

In message , Vortex3
writes

I am told hard disk heads contain very powerful "rare earth" magnets. Since
I have an old crashed disk here I will begin by extracting its magnets later

D


They do indeed, I needed a magnet to hold a shower cubicle door open
last week and had an old HD that was in need of permanent trashing so I
opened it and took the magnets out. One of those glued to the door edge
and a steel based penny to the wall worked fine. I let the two magnets
hold on to each other and had a bit of a struggle to pull them apart!

--
Bill

"Vortex3" wrote in message
...
Hello,


I have 2 magnetic compasses, one of which for some mysterious reason has
reversed polarity ie. red points south!!!!

Pic he http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?


D


The job is now done! Not difficult! No electricity needed.

I took a powerful magnet from an old HDD, and with a bit of careful
"stroking" (oooer missus) the problem is solved.

Pix he http://home.btconnect.com/vortex/compass/

D

"Richard Savage" wrote in message
...
On Feb 7, 12:06 am, Jason wrote:
Invisible Man wrote:
Vortex3 wrote:
Hello,

I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!

Pic he http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?

D

Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.

The correct direction is the one that works ;-)

This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

Arfa

Arfa Daily wrote:
"Richard Savage" wrote in message
...
On Feb 7, 12:06 am, Jason wrote:
Invisible Man wrote:
Vortex3 wrote:
Hello,
I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!
Pic he http://home.btconnect.com/vortex/paradox.jpg
The RH compass in the picture is correct.
The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.
Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!
Can anybody suggest a non-destructive method to correct this?
D
Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.
The correct direction is the one that works ;-)

This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

Arfa


I was thinking that - but remembered that thing called 'night',
especially 'moonless night with no stars'.

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

Arfa Daily expressed precisely :
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

Or can see which side the moss is growing on the trees, again assuming
you know which hemisphere you are in.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Harry Bloomfield" wrote in message
k...
Arfa Daily expressed precisely :
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

Or can see which side the moss is growing on the trees, again assuming you
know which hemisphere you are in.

--
Regards,
Harry (M1BYT) (L)

Can you not just empty a sink to decide which hemisphere you are in?

Adam

On Sat, 07 Feb 2009 20:26:08 GMT, ARWadsworth wrote:

"Harry Bloomfield" wrote in message
k...
Arfa Daily expressed precisely :
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

Or can see which side the moss is growing on the trees, again assuming you
know which hemisphere you are in.

--
Regards,
Harry (M1BYT) (L)

Can you not just empty a sink to decide which hemisphere you are in?

Adam

yebbut, then you need to know which way up you are.

Not of use in 'wilderness', but TV dishes tend to point towards the
Equator; in the UK they're about 20 - 30 deg. E of S.
--
Peter.
You don't understand Newton's Third Law of Motion?
It's not rocket science, you know.

"Fred" wrote in message
...

"Vortex3" wrote in message
...


Can anybody suggest a non-destructive method to correct this?

My best guess would be that it has been sat for a long time with the
needle pointing in the wrong direction, with the case tilted just enough
to prevent the needle swinging and the earths field has managed to
remagnetise it with the wrong polarity.

You need to tilt it enough to again jam the needle and then stroke the
end of a strong magnet along the full length of the needle. It needs the
strokes to be done in one direction - lift the magnet at the end of each
stroke well away, then start fresh stroke. It might need some practise
not to get the magnet so close that it makes the needle move.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk



Cheers Harry,

I will try this approach first!

I am told hard disk heads contain very powerful "rare earth" magnets.
Since I have an old crashed disk here I will begin by extracting its
magnets later


I'm not so sure about hard disks having strong magnets in them. The head
is a strong electromagnet but it only over a very small area!

If I wanted a strong magnet I'd aim for a magnetron in a microwave.

No, paradoxically the strongest magnets you are likely to encounter
are from the head actuator of a hard-drive. The ring magnets from
oven magnetrons aren't in the same league.
Trust me on this, I have a pair of each on the table as I type this!

--
Graham.

%Profound_observation%

On 7 Feb, 00:30, "Arfa Daily" wrote:
"Andy Dingley" wrote in message

You're unlikely to do it with a battery, as you won't get enough
current.

How much current are you figuring on needing then ? The average car battery
is good for at least 200 amps, and more if it's a big 'un ...

It's not good for 200A into an inductive load though.

It's not ampere turns, as suggested, unless you have a true solenoid
(or good approximation). That means a _long_ solenoid, which means yet
more inductance. You're better with a coil that's only 3 - 4 times
the length (if I felt like the maths, I'd work it out properly) as
that's the maximum of efficient magnetic behaviour (i.e. most useful
flux through the needle) vs. fall off in achievable current through
the circuit.

"Andy Dingley" wrote in message
...
On 7 Feb, 00:30, "Arfa Daily" wrote:
"Andy Dingley" wrote in message

You're unlikely to do it with a battery, as you won't get enough
current.

How much current are you figuring on needing then ? The average car
battery
is good for at least 200 amps, and more if it's a big 'un ...

It's not good for 200A into an inductive load though.

A battery is DC!
After a few milliseconds 200A into a coil is easy.

On Feb 8, 3:42 am, "Arfa Daily" wrote:

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

It's easy for me. At night I just look for the Southern Cross. That
tells me accurately where South is. I don't need a compass

Andy Dingley wrote:
On 7 Feb, 00:30, "Arfa Daily" wrote:
"Andy Dingley" wrote in message

You're unlikely to do it with a battery, as you won't get enough
current.
How much current are you figuring on needing then ? The average car battery
is good for at least 200 amps, and more if it's a big 'un ...

It's not good for 200A into an inductive load though.



200A is 200A, no matter waht its into.


It's not ampere turns, as suggested, unless you have a true solenoid

Its ampere turns whatever you have.

The "*constant*" varies with the length of the solenoid, that's all.


(or good approximation). That means a _long_ solenoid, which means yet
more inductance. You're better with a coil that's only 3 - 4 times
the length (if I felt like the maths, I'd work it out properly) as
that's the maximum of efficient magnetic behaviour (i.e. most useful
flux through the needle) vs. fall off in achievable current through
the circuit.

"Rod" wrote in message
...
Fred wrote:
"Vortex3" wrote in message
...

Can anybody suggest a non-destructive method to correct this?
My best guess would be that it has been sat for a long time with the
needle pointing in the wrong direction, with the case tilted just
enough to prevent the needle swinging and the earths field has managed
to remagnetise it with the wrong polarity.

You need to tilt it enough to again jam the needle and then stroke the
end of a strong magnet along the full length of the needle. It needs
the strokes to be done in one direction - lift the magnet at the end of
each stroke well away, then start fresh stroke. It might need some
practise not to get the magnet so close that it makes the needle move.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


Cheers Harry,

I will try this approach first!

I am told hard disk heads contain very powerful "rare earth" magnets.
Since I have an old crashed disk here I will begin by extracting its
magnets later


I'm not so sure about hard disks having strong magnets in them. The head
is a strong electromagnet but it only over a very small area!

If I wanted a strong magnet I'd aim for a magnetron in a microwave.


The motor that positions the head is based on a strong magnet. In my
experience, fairly easy to open up and remove (might require a Torx
driver).

Suggest you only do this to redundant drives as re-assembly is not the
reverse of dis-assembly. (Haynes passim.) :-)


I forgot about that part!! Floppy disc drives have a similar same open type
motor as presumably do CD drives.

"Andy Dingley" wrote in message
...
On 7 Feb, 00:30, "Arfa Daily" wrote:
"Andy Dingley" wrote in message

You're unlikely to do it with a battery, as you won't get enough
current.

How much current are you figuring on needing then ? The average car
battery
is good for at least 200 amps, and more if it's a big 'un ...

It's not good for 200A into an inductive load though.

It's not ampere turns, as suggested, unless you have a true solenoid
(or good approximation). That means a _long_ solenoid, which means yet
more inductance. You're better with a coil that's only 3 - 4 times
the length (if I felt like the maths, I'd work it out properly) as
that's the maximum of efficient magnetic behaviour (i.e. most useful
flux through the needle) vs. fall off in achievable current through
the circuit.

The effect of any inductance is soon lost when driven with a DC voltage,
where after a short time any coil looks like a resistance!

Fred wrote:

I forgot about that part!! *Floppy disc drives have a similar same open
type motor as presumably do CD drives.

All the floppy drives I've pulled apart use a little stepper motor and
screwed shaft to drag the head slowly across the disk.

--
Mike Clarke

In message , Rod
writes
Arfa Daily wrote:
"Richard Savage" wrote in message
...
On Feb 7, 12:06 am, Jason wrote:
Invisible Man wrote:
Vortex3 wrote:
Hello,
I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!
Pic he http://home.btconnect.com/vortex/paradox.jpg
The RH compass in the picture is correct.
The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.
Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!
Can anybody suggest a non-destructive method to correct this?
D
Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.
The correct direction is the one that works ;-)
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)
Richard
Well than ain't hard if you can see where the sun is, and you know
which hemisphere you're in ...
Arfa
I was thinking that - but remembered that thing called 'night',
especially 'moonless night with no stars'.

Then you should stay indoors in case the ghoulies get you


--
geoff

Fred wrote:

The motor that positions the head is based on a strong magnet. In my
experience, fairly easy to open up and remove (might require a Torx
driver).

I forgot about that part!! Floppy disc drives have a similar same open type
motor as presumably do CD drives.


Er, Nope. This is not the motor that spins the disc. In a hard disk,
it's the actuator for positioning the head.

Top left hand bit of the second picture on
http://computer.howstuffworks.com/hard-disk5.htm

Have a look at the pictures that David eventually put up, or take a dead
thing to bits yourself. :-)

--
Adrian C

"PeterC" wrote in message
...
On Sat, 07 Feb 2009 20:26:08 GMT, ARWadsworth wrote:

"Harry Bloomfield" wrote in message
k...
Arfa Daily expressed precisely :
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know
which
hemisphere you're in ...

Or can see which side the moss is growing on the trees, again assuming
you
know which hemisphere you are in.

--
Regards,
Harry (M1BYT) (L)

Can you not just empty a sink to decide which hemisphere you are in?

Adam

yebbut, then you need to know which way up you are.

Not of use in 'wilderness', but TV dishes tend to point towards the
Equator; in the UK they're about 20 - 30 deg. E of S.
--
Peter.

I can't help thinking is must have been a good party if you wake up in the
morning with no idea on which hemispere you are on and you need to find your
way north.

Adam

ARWadsworth wrote:
"PeterC" wrote in message
...
On Sat, 07 Feb 2009 20:26:08 GMT, ARWadsworth wrote:

"Harry Bloomfield" wrote in message
k...
Arfa Daily expressed precisely :
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)

Richard

Well than ain't hard if you can see where the sun is, and you know
which
hemisphere you're in ...
Or can see which side the moss is growing on the trees, again assuming
you
know which hemisphere you are in.

--
Regards,
Harry (M1BYT) (L)
Can you not just empty a sink to decide which hemisphere you are in?

Adam
yebbut, then you need to know which way up you are.

Not of use in 'wilderness', but TV dishes tend to point towards the
Equator; in the UK they're about 20 - 30 deg. E of S.
--
Peter.

I can't help thinking is must have been a good party if you wake up in the
morning with no idea on which hemispere you are on and you need to find your
way north.

Adam


I couldn't help wondering, what colour was the bear?

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

On Sun, 08 Feb 2009 17:27:34 +0000, Rod wrote:

yebbut, then you need to know which way up you are.

Not of use in 'wilderness', but TV dishes tend to point towards the
Equator; in the UK they're about 20 - 30 deg. E of S.
--
Peter.

I can't help thinking is must have been a good party if you wake up in the
morning with no idea on which hemispere you are on and you need to find your
way north.

Adam

I couldn't help wondering, what colour was the bear?

the bear what?
--
Peter.
You don't understand Newton's Third Law of Motion?
It's not rocket science, you know.

On Feb 9, 5:42 am, Adrian C wrote:
Fred wrote:

The motor that positions the head is based on a strong magnet. In my
experience, fairly easy to open up and remove (might require a Torx
driver).

I forgot about that part!! Floppy disc drives have a similar same open type
motor as presumably do CD drives.

Er, Nope. This is not the motor that spins the disc. In a hard disk,
it's the actuator for positioning the head.

Top left hand bit of the second picture onhttp://computer.howstuffworks.com/hard-disk5.htm

Have a look at the pictures that David eventually put up, or take a dead
thing to bits yourself. :-)

Just use a compass to find the magnet. I believe the Silva brand is
good for that

"Andy Dingley" wrote in message
...
On 7 Feb, 00:30, "Arfa Daily" wrote:
"Andy Dingley" wrote in message

You're unlikely to do it with a battery, as you won't get enough
current.

How much current are you figuring on needing then ? The average car
battery
is good for at least 200 amps, and more if it's a big 'un ...

It's not good for 200A into an inductive load though.

It's not ampere turns, as suggested, unless you have a true solenoid
(or good approximation). That means a _long_ solenoid, which means yet
more inductance. You're better with a coil that's only 3 - 4 times
the length (if I felt like the maths, I'd work it out properly) as
that's the maximum of efficient magnetic behaviour (i.e. most useful
flux through the needle) vs. fall off in achievable current through
the circuit.

What, so a starter motor is not an inductive load then ? Of course a car
battery can drive 200 amps through an inductive load. It will take a few mS
for the current to ramp up to that level, but providing that everything
holds out for long enough, and the DC resistance of the winding is low
enough to allow it, it *will* get there.

Arfa

On Feb 7, 3:57*pm, Rod wrote:
Arfa Daily wrote:
"Richard Savage" wrote in message
....
On Feb 7, 12:06 am, Jason wrote:
Invisible Man wrote:
Vortex3 wrote:
Hello,
I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!
Pic hehttp://home.btconnect.com/vortex/paradox.jpg
The RH compass in the picture is correct.
The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.
Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!
Can anybody suggest a non-destructive method to correct this?
D
Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.
The correct direction is the one that works ;-)

This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. *:-)

Richard

Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...

Arfa

I was thinking that - but remembered that thing called 'night',
especially 'moonless night with no stars'.

A compass won't be much use if you can't see where you are going. Wait
until sunrise.

MBQ

On Feb 7, 1:56*pm, "Vortex3" wrote:
"Vortex3" wrote in message

...



Hello,

I have 2 magnetic compasses, one of which for some mysterious reason has
reversed polarity ie. red points south!!!!

Pic he * * * * *http://home.btconnect.com/vortex/paradox.jpg

The RH compass in the picture is correct.

The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. *I have no idea how this
happened.

Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!

Can anybody suggest a non-destructive method to correct this?

D

The job is now done! *Not difficult! *No electricity needed.


No, you can't possibly have done. Someone on UseNet said it couldn't
be done, therefore you must be mistaken.

"Buy a new compass. The power needed to re-magnetise it reliably from
outside the sealed vial is going to be considerably more than that
needed to do a bare needle - I suspect impractically so."

MBQ

Man at B&Q wrote:
On Feb 7, 3:57 pm, Rod wrote:
Arfa Daily wrote:
"Richard Savage" wrote in message
....
On Feb 7, 12:06 am, Jason wrote:
Invisible Man wrote:
Vortex3 wrote:
Hello,
I have 2 magnetic compasses, one of which for some mysterious reason
has reversed polarity ie. red points south!!!!
Pic hehttp://home.btconnect.com/vortex/paradox.jpg
The RH compass in the picture is correct.
The LH compass is a really nice 35 year old SILVA "Type 4" that points
precisely 180 degrees in the wrong direction. I have no idea how this
happened.
Bear in mind the needle is in a sealed oil filled housing, it is not
practically possible to dismantle it!
Can anybody suggest a non-destructive method to correct this?
D
Lock it and then run one pole of a permanent magnet along it a number of
times. Not sure which way round though.
The correct direction is the one that works ;-)
This raises the question which is never answered by the 'survive on
your own' books which helpfully explain how to magnetise a needle for
compass purposes but never tell you how to work out the direction that
the needle points. :-)
Richard
Well than ain't hard if you can see where the sun is, and you know which
hemisphere you're in ...
Arfa
I was thinking that - but remembered that thing called 'night',
especially 'moonless night with no stars'.

A compass won't be much use if you can't see where you are going. Wait
until sunrise.

MBQ

We had the 'walk in total darkness' thread a few weeks ago ... and I've
been practising. :-)

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

On Sun, 08 Feb 2009 17:23:14 GMT, "ARWadsworth"
wrote:

I can't help thinking is must have been a good party if you wake up in the
morning with no idea on which hemispere you are on and you need to find your
way north.

One night in the early 90's in Sweden I somehow ended up in what
seemed the middle of absolutely nowhere at a party. It seemed at the
time a good idea to join in the fun except I had a flight back home
via at about 7am, a short stopover in Copenhagen and a meeting late
afternoon back in the UK. As the night progressed I realised there
was no mobile phone coverage and getting a taxi could have taken hours
due to not speaking much Swedish, me not knowing the number of any
taxi companies, and everyone at the party who might have been able to
help being completely rat arsed.

Fortunately It was midsummer and good weather so at about 4am I
started walking in what I thought was the right direction by spotting
a building on the horizon, the rising sun was no real help as I hadn't
a clue where I was. If I headed in the wrong direction the next stop
could be Norway. I eventually got back to my hotel, 'slept' in my
bed for all of 20 minutes, then woke and left by prearranged taxi for
the airport 5 minutes later. Until I got a few strong cups of coffee
down me at the airport I really wasn't sure what planet I was on let
alone what hemisphere.

There haven't been many occasions when I've totally passed on the SAS
business class lounge at Copenhagen where one of the most notable
features is that the beer pumps are on the customers side of the bar,
but this was one of them. Despite visiting many times since and
getting to know the local area quite well I still haven't a clue where
that party was


--