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Improvised Compass

by Rob Bicevskis

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Experiment number one was to rub all of samples in the above table to see if there is any difference in the rotation times.

Envelope please....

There was no difference in the pins/needles ability to point north after being rubbed with silk.

The pins/needles that were previously non-magnetic remained that way. The pins/needles that previously has some level of magnetism continued to have "about" as much. (I used the word "about" since the exact number of seconds did vary by a tiny bit. This is all about "experimental error.") The important point here is that as far as making a compass is concerned, rubbing the pins/needles with silk did nothing.

Experiment number two was to rub the samples with fur/hair. I used a deer tail, rabbit fur, and my own hair.

In all cases, none of the samples were affected.

Experiment number three was to demagnetize all of the samples and then try all of the tests one more time.
This is the setup that I used to demagnetize the pins/needles. The objects at the left of the photo are solenoids. They are basically big coils of wire. To the right is a Variac - which is more or less a transformer or power supply. The control on top allows one to vary the output (AC) voltage. In the middle is a multi-meter which I used to monitor the amount of current going through the solenoids so that I wouldn't over-stress them.

In brief, imagine that ferromagnetic metals are built up of many tiny magnets. Normally all of these little magnets point in random directions. In this state, the metal is not considered a magnet. When something is magnetized, then a number of these little magnets (domains) line up in the same direction and we end up with a net magnetic force.

If we want to remove the magnetism from a object, then there is a well known way to do this. We expose our magnet to an intense time-varying magnetic field. Basically we apply an external magnetic field that is flipping from N to S many times a second. All of those little magnetic domains that are in our sample get flipped back and forth so many times that they become non-aligned and there is no net external magnetic field. If you want more details, do a search on demagnetizers.

After demagnetizing all of the samples, I verified first that they were indeed non-magnetic by floating them and checking that there was no bias to point in any particular direction. This proven, I then rubbed them with silk, fur and hair, and you can probably guess by now what the results were:

None of the demagnetized samples, either before, or after being rubbed by silk/fur/hair showed any ability to act as a compass.

Razor Blades
Ok, ok, well the write-ups say that you can make a compass with a razor blade. That one's gotta work, right?

I only used one type of razor blade. Floating the razor blade was as easy as floating the pins/needles.

The first one that I floated immediately pointed north. Once again, I had done nothing to this razor blade. It was new and unused.

As with the pins/needles, I demagnetized the razor blade. After confirming that it was indeed de-magnetized, I rubbed it with the silk/fur/hair and once again, the razor blade would not act as a compass.

Conclusions from the Experiments

The experiments support the original hypotheses and contradict what the survival books/websites would have you believe. One of the most interesting results is that many pins/needles come pre-magnetized - supporting the hypothesis that in the cases where some people have actually tried this improvised survival technique, they are not getting a true result, but a false positive!

I have left out a lot of theory/details about how magnets and electrostatics work. There is a lot of good information already "out there" so I haven't tried to reproduce it here.

Of course, this does lead to a big problem, what do you believe? If you were to read survival books and look at various internet references, you would believe that you could create a compass with a pin and a piece of silk. This leads to a much bigger discussion about the accuracy of anything that you read, or about what is "common knowledge." In the end, why should you even believe what I have documented? The good news is, that if you care about the answer, then it's only going to take a dollar or two of stuff and an hour or two of your time to reproduce my results!


What does Work?

We've discussed what doesn't work. So how about a bit of info on what does work?



18-15. You can construct improvised compasses using a piece of ferrous metal that can be needle-shaped or a flat double-edged razor blade and a piece of thread or long hair from which to suspend it. You can magnetize or polarize the metal by slowly stroking it in one direction on a piece of silk or carefully through your hair using deliberate strokes.

You can also polarize metal by stroking it repeatedly at one end with a magnet. Always stroke in one direction only.

If you have a battery and some electric wire, you can polarize the metal electrically. The wire should be insulated. If it is not insulated, wrap the metal object in a single, thin strip of paper or a leaf to prevent contact. The battery must be a minimum of 2 volts. Form a coil with the electric wire and touch its ends to the battery’s terminals. Repeatedly insert one end of the metal object in and out of the coil. The needle will become an electromagnet. When suspended from a piece of nonmetallic string, or floated on a small piece of wood, cork or a leaf in water, it will align itself with a north-south line.

Quote taken from:
FM 3-05.70  (FM 21-76 US Army Survival Manual)
Field Manual Headquarters
No. 3-05.70 Department of the Army
Washington, DC, 17 May 2002
Section 18-8

To be fair, let's go back to the entire section from the US Army Survival Manual.

We see that two other methods are mentioned:

  1. Stroking the pin/needle with a magnet.
  2. Wrapping the pin/needle with wire and connecting it to a battery of at least two volts.


These other two methods are at least sound. Stroking the pin/needle with a magnet is a well known way of transferring magnetism. Wrapping a pin/needle with wire and passing a current through the wire is also well supported.

Of course, there is one little red herring here, the description says that the battery has to be at least 2 volts. Why is this? I don't know. More misleading information? Time to analyze and experiment!

First let's have a look at stroking a pin/needle with a magnet. We don't need a "classical" stand-alone magnet. We probably have all sorts of magnets all around us.

One use of magnets is in headphones. Often, the magnets will be shielded in some way. A simple test to see if they are good enough is to touch a pin/needle to the magnet or place where you believe the magnet to be. If the needle "sticks" or is held the the magnetic field, then that's about all you need.

In the picture to the left, I placed a pin on cover at the back of an earphone. The pin held in place when I lifted up and turned the headphone. I took off the pin and it made a fine compass. Yes, stroking the pin repeatedly will increase the field (to a point), but it doesn't take much to magnetize a pin/needle.

Yes, this works.

Now for a bit of theory. In the drawing to the left, figure 1 shows a simplified view of what the magnetic field (red) might look like when a current is passed through a wire (blue.) The greater the current that flows through the wire, the greater the magnetic field.

The next drawing shows what happens when we coil the wire. The magnetic field joins around the turns of wire. In this case, the magnetic field is stronger. Each turn of the wire contributes. If we have 10 turns of wire, then the field will be 10 times stronger.

As in drawing 3, if we put a piece of ferromagnetic material into the coil and pass a current through the wire, the metal will act as an electro-magnet. What happens when we turn of the current? Going back to our previous discussion about magnetic domains, while the metal is under the influence of the electro-magnetic field, some of the domains become aligned. When we remove the current, these domains stay aligned - and behold we have a magnet. (This drawing also applies to the demagnetizer. It is basically drawing 3, except the coil is fed with AC instead of DC.)

So, if we want to get a magnetized piece of metal, we just need to put it into an energized coil and we're done. The more turns of wire we have, the better, and the higher the current (voltage) the better.

But there's one more part here... The manual says: The battery must be a minimum of 2 volts.

Once again this misleading. There is no issue of a minimum threshold of voltage. I don't know where the 2 volts came from. Possibly from some battery technology that the army used at some point? Anyway, all that matters is we try to maximize the number of turns of wire, and that we pass a current through the wire. (As always, things aren't exactly that simple. As we add more turns of wire, the wire is probably longer, and therefore presents a larger resistance to the flow of electricity.) If the wire is too thick, and the current too high, we will burn up the whole assembly. On the other hand, using thousands of turns of wire is unnecessary.
Here is one way of magnetizing our pin.

Thin, insulated wire was wrapped around a piece of drinking straw. In this case, the wire was about 2 metres in length and ended up allowing for 90 turns.

A pin was inserted into the straw and the wire was connected to a 1.5V D cell. From the photo, it can be seen that the pin is held suspended in coil. This is happening strictly by the created magnetic field.

Did it work. Of course. After floating the needle, it turned north in less an a second.

So we validated the method, but also dispelled the limitation of a 2V minimum voltage.

Do we really need a big battery?


An AAA battery worked just a well.

The size of the battery is important, and isn't.


A watch battery worked fine too.

All of the batteries are 1.5V batteries. A bigger battery can supply more current over a longer period of time. Since it only takes a second or two to magnetize our pin, even a watch battery can supply enough current to do the job.

A higher voltage will create a bigger field and a better magnet. So, if you have lots of batteries, or some other source of electricity, by all means, use it - but it's clearly no required.

(The previous statement has limitations, but that's beyond the scope of this webpage.)

Conclusions on Using Magnets and Electromagnets

We showed a couple of methods that actually do work. Although, if we already have a magnet, it doesn't seem like a great leap to think that we could find north. Just floating the magnet would do the trick.

The 2V limitation was clearly shown to be false. I only went as low as 1.5V - since that is the smallest voltage produced by any "normal" batteries. It's simple physics that going much lower will also produce a working magnet. The most interesting thing here is that once again we can see how silly things get perpetuated. Try an internet search on "improvised compasses" and "2 Volts." Again, many just blindly copying from one another!

For bonus points, here's something else to think about. In the US Army description of the above two types of compass (stroking on a magnet and using an electromagnet) there are a few other things they mention.

When using an existing magnet, the directions are: You can also polarize metal by stroking it repeatedly at one end with a magnet. Always stroke in one direction only.

For the electromagnet: Repeatedly insert one end of the metal object in and out of the coil.

If you look at the three hand-drawings above, notice that when the coil is energized, one side is N and the other is S. If you move the pin/needle in and out of the coil, then you are exposing the item to alternating N and S poles. Sounds more like a demagnetizer to me. Maybe that's why they need a 2V battery? (Just kidding.) Anyway, think about this one a bit!


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