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Car Forum / Land Rover Cars / February 2007So OT as to be extra-planet! Compass needles - which end points north?
Been reading my Book of Dangerous Things for Boys and came across the chapter about navigation. Now we all know that stroking a needle in one direction repeatedly with something such as silk or fur will magnetise said needle such that it will, if suitably suspended, point north. But how do we know which end is pointing north? TIA Richard > Been reading my Book of Dangerous Things for Boys and came across the > chapter about navigation. Now we all know that stroking a needle in [quoted text clipped - 5 lines] > > Richard My own view would be the thickest part as it has most magnetism.  Signature'I'll be back......' Nige Subaru WRX (54) Land Rover Discovery II BMW 650 GS Dakar 2000 Suzuki GSX1300R Y Hayabusa > 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 > Been reading my Book of Dangerous Things for Boys and came across the > chapter about navigation. Now we all know that stroking a needle in > one direction repeatedly with something such as silk or fur will > magnetise said needle such that it will, if suitably suspended, point > north. 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. > But how do we know which end is pointing north? 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 > 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. 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. SignatureBlast off and strike the evil Bydo empire! > Been reading my Book of Dangerous Things for Boys and came across the > chapter about navigation. Now we all know that stroking a needle in one > direction repeatedly with something such as silk or fur will magnetise > said needle such that it will, if suitably suspended, point north. But > how do we know which end is pointing north? 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; http://www.camping-canada.com/Compass_e.asp SignatureBlast off and strike the evil Bydo empire! >>Been reading my Book of Dangerous Things for Boys and came across the >>chapter about navigation. Now we all know that stroking a needle in one [quoted text clipped - 3 lines] > > 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. Exactly my point. > 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; > > http://www.camping-canada.com/Compass_e.asp 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? > Thank you. That is exactly the answer I sought! 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. <hard question pointedly deleted> SignatureBlast off and strike the evil Bydo empire! >> Thank you. That is exactly the answer I sought! > [quoted text clipped - 3 lines] > > <hard question pointedly deleted> 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 >>> Thank you. That is exactly the answer I sought! >> [quoted text clipped - 12 lines] > > Steve i may be wrong, but, isnt magnetic north 8-degrees towards east from true north??? > i may be wrong, but, > isnt magnetic north 8-degrees towards east from true north??? Magnetic north is about 11 degrees off true north at the moment, and its changing pretty rapidly anyway. Steve >> i may be wrong, but, >> isnt magnetic north 8-degrees towards east from true north??? [quoted text clipped - 3 lines] > > 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 > 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. > 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. Its picking up speed at the moment - 40 odd km/year, from 9km/year. Steve They do say it is getting ready to flip. SignatureLarry Series 3 Rust and Holes > > Its picking up speed at the moment - 40 odd km/year, from 9km/year. > > Steve > They do say it is getting ready to flip. It's all Tony Blair's fault! SignatureBlast off and strike the evil Bydo empire! >> 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. > > Its picking up speed at the moment - 40 odd km/year, from 9km/year. 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... On Sunday, in article <%%lEh.26485$OK6.61@newsfe4-win.ntli.net> jps@supanet.com > >> 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 [quoted text clipped - 5 lines] > and vice-versa. Prolly every million years, not something likely to cause us > bother... We don't know how long a flip takes, not what effects it might have on the solar wind. At least we're not so dependent on magnets for navigation as we were even 20 years ago. The timing isn't predictable, but there might be enough warning to get a lead-lined hat. I reckon it's one of those things that is currently best regarded as something to keep scientists away from the dangeous stuff. SignatureDavid G. Bell -- SF Fan, Filker, and Punslinger. On the horizon, a carrier task force of the Salvation Navy was turning into the wind, preparing to launch Zeppelins. >> 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. > >Its picking up speed at the moment - 40 odd km/year, from 9km/year. that's 'cos it's a circular motion and from where we're sitting it moves at a speed governed by a sinusoidal relationship. exactly like the way day-length varies, only over a longer period. The fastest changes are at the midpoint, which is in a few years for magnetic north (or mebbe in a year or so) and in about a month for day-length. one map here says 4 degrees west of grid north and shifting half a degree in 4 years, for 1999. which means that by now it's more like 3 degrees. another one says 5½ degrees west in 1986, moving by half a degree in the next 3 years. if you find old maps, from say about 1940, it was about 11 degrees. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > Been reading my Book of Dangerous Things for Boys and came across the > chapter about navigation. Now we all know that stroking a needle in one > direction repeatedly with something such as silk or fur will magnetise > said needle such that it will, if suitably suspended, point north. But > how do we know which end is pointing north? 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. > > Been reading my Book of Dangerous Things for Boys and came across the > > chapter about navigation. Now we all know that stroking a needle in one [quoted text clipped - 11 lines] > > Julian. 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 >>Been reading my Book of Dangerous Things for Boys and came across the >>chapter about navigation. Now we all know that stroking a needle in one [quoted text clipped - 11 lines] > > Julian. 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. > 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. "> > 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. > >Funny enough I thought satnav was the answer until I went sailing in the Med. The satnav is so accurate it can tell you which end of the boat you are on, but the charts which were last surveyed in the 1800's, can be up to a mile out! TonyB > " > [quoted text clipped - 5 lines] > > Julian. Avast me hearties and prepare for boarding! Richard ;-) > Been reading my Book of Dangerous Things for Boys and came across the > chapter about navigation. Now we all know that stroking a needle in one [quoted text clipped - 5 lines] > > Richard Sun rises in the East sets in the West, so get uo at sunrise and find North then paint needle. You could also use a GPS hand set and set it ???!!!??? Is'nt there a way of using the hands on a watch and studying the shadow produced by a twig placed at the centre with the hour hand pointing to the sun ? |
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