How to find north?

[George Miles]

oh yes, i seem to recall from swallows and amazons that its the end of the saucepan pointing upwards to the north star, not the handle.

[g]

[williamwright]

When I was at school we were told to always pass a pair of compasses with the sharp point away from the person you were passing them to. When he was feeling in need of sado-sexual stimulation the teacher used to ask one of the prettier boys to pass him a pair of compasses. If the boy got it the wrong way round the teacher would cane him on the arse. They were different times.

Bill

[The Natural Philosopher]

More or less, yes. Its good enough for rough orienteering, but not for bombinbg Berlin

[Harry Bloomfield, Esq.]

Cursitor Doom expressed precisely :

Compasses do loose their magnetism slowly over time, so will settle less quickly.

[Harry Bloomfield, Esq.]

Max Demian submitted this idea :

I had one of those, of course they had to be heavily damped, with so much movement in a vehicle, just like a ships compass. They were handy in helping prevent you going in the completely wrong direction, if you knew which direction you were trying to go.

[Harry Bloomfield, Esq.]

It happens that Max Demian formulated :

Use the satnav?

[Andrew]

Follow the migrating birds as the Northern Hemisphere exits winter ?.

[Andrew]

Mine lost some of its oil and bubble stopped the gubbins turning.

[Cursitor Doom]

I found these very useful back in the day; not so much now, though. I've had cars where the magnetism generated once the engine started running knocked the compass for six. It would settle in the wrong direction and remain there, fixedly all the time the engine was running. I could drive all around a patch of waste ground in a circle and the compass didn't budge a milimeter; just stuck on the same bearing regardless of the direction driven. Too much electronics in modern cars I reckon.

[Chris Green]

I can't imagine much magnetism that turns on and off when you stop and start the engine. Electronic devices don't, in them main, have electromagnets in them. Loudspeakers and such which do have magnets in them have permanent magnets so they won't go on and off.

[nothanks]

When a current flows in any conductor it causes a magnetic field around it (look-up Biot-Savart), that's how motors work (look-up Faraday). These magnetic fields are a big problem in vehicles that need magnetic sensors (compasses and magnetometers) and is why "compass swings" are performed with all electrical services running. A compass swing involves adjusting small magnets in the compass to minimise the errors caused by the vehicle magnetism, the residual errors are then published on a Deviation card and used to correct the compass indication when an accurate magnetic measurement is required. Usually the deviation is sufficiently small that it can be ignored, but woe betide the pilot who leaves a headset on the coming (sp?).

[The Natural Philosopher]

Coaming. Didnt know that term was in use in aircraft. It's nautical originally:

"Coaming is any vertical surface on a ship designed to deflect or prevent entry of water. It usually consists of a raised section of deck plating around an opening, such as a hatch. Coamings also provide a frame onto which to fit a hatch cover.

The protective metal sheeting or plating protecting against water entry into ventilation shafts in large ships is called a coaming as it suits this purpose.

The term was borrowed by the aviation industry to refer to a low rim around the opening for an unenclosed cockpit"

[Chris Green]

The magnetic fields produces by current flowing in wire are *very* small compared with those of large chunks of steel (as cars are mostly made of) and the permanent magnets in loudspeakers and such (which cars have).

[nothanks]

... and the Earth's magnetic field is also very small. My response was based on knowledge and experience, rather than googling.

[The Natural Philosopher]

And he is wrong. it all depends on the current, 16A charging a battery is a decent field strength, for example.

I remember experiments with compasses moving when a single wire passed current