So OT as to be extra-planet! Compass needles - which end points north?

My own view would be the thickest part as it has most magnetism.

Er, possibly but any ferromagnetic material can be made to perform as a compass needle, i.e. I don't think it is shape dependent - remember those compasses with the little slide on the side to stop the needle bouncing about that we had as children? The needle on them IIRC was a slim rectangle with a huge dollap of luminous paint at one end to show north.

Richard

No. You need another magnet for that. You're thinking of static electricity. Rub a piece of plastic with a cat and you can generate sparks and get claw marks on your hands.

If you know which hemisphere you are in (it must have been a really bad accident to leave you unsure) the sun will give you a clue. Even with a lot of cloud cover you can tell roughly which way it is and in the northern hemisphere it is always more south than north.

nigelH

Get a proper compass and check!

It's odd but I can see lots of pages about how to make compasses out of bits of snot or whatever but hardly any of them tell you how to read the damned thing, e.g. which end points north.

The most often repeated bit is that if you stroke from end A to end B, then end B will point north. Here's an example;

Apparently you can do it, I've seen it on loads of websites so IT MUST BE TRUE I'm sure you'll agree ;-)

So best carry that cat with you in case you need to rub any needles with it. Once you've made a compass with the cat, then you can eat the cat for sustenance.

;-)

Exactly my point.

Thank you. That is exactly the answer I sought!

Now, who is going to explain why the magnetic domains align N-S with S away from the start of stroke? Surely if their magnetic characteristics are identical one stands an equal chance of producing a magnetic needle that points to magnetic south?

Go outside at midday. The sun will be at its most southerly point in the sky. (dead easy this time of year because it is still fairly low in the sky) North is t'other direction!

Surely you've noticed which of your rooms get the sun through the window at midday - there's your biggest clue. Remember that it doesn't point at the north pole, but points at magnetic north, they're a few degrees apart.

Julian.

Personally I'd check that if I were you, as in try it out for yourself and see, just in case you end up floating about in the middle of the atlantic with a dingy, a pin and a set of cami-nickers.

You CAN guarantee a magnets polarisastion if its made by hitting it with a bloody big hammer, whilst it is angled at the local angle of dip of the earth´s field. North is the top bit.

Otherwise, half a days work in sunlight gives you geographical north, and your magnet points to some approximation of "north"

Steve

i may be wrong, but, isnt magnetic north 8-degrees towards east from true north???

Can't see as it makes any difference as the compass will stop you from wandering round in circles. Doesn't matter if you're going north or south as you will be travelling objectively *with* the compass.

Martin

Magnetic north is about 11 degrees off true north at the moment, and its changing pretty rapidly anyway.

Steve

It does depend where and when you are. I didn't know the variation went up to 11 degrees. For the OS sheet 128 which is where I live, true north and grid north are the same at the NW and SW corners of the map, and true north is about half a degree W of grid north at the other two corners. To complicate things, at the centre of the sheet, mag north was 14 minutes W of grid north in the year 2000 and is moving 12 minutes E per annum. I've also got an Admiralty chart of the Irish Sea by N Wales in front of me and in 2002 mag N was 4 degrees 55 minutes W of true N, moving 9 minutes E per annum. No wonder it's so easy to get lost :-)) Cheers Graham

That approximation works pretty well for much of the UK with only local variations. It's moving east, as you say, so many of us here will be around when magnetic and true north coincide. That'll make life easier for navigators!

When I was at school magnetic N was in the Hudson Bay area. And so, of course, depending on where you are on the surface of the globe variation can be east or west of true.

I know where NSEW are here. It was a purely intelectual question based upon the information in the book and how dubious the value of that information is in isolation.

Well it made you think then, so I suppose the author achieved his objective :-)

I don't suppose the material was intended as course study material for naval officers...

Julian.

Its picking up speed at the moment - 40 odd km/year, from 9km/year.

Steve

They do say it is getting ready to flip.

And ISTR every so often it does a 'U' turn, ie south ends up in the north and vice-versa. Prolly every million years, not something likely to cause us bother...