>> university notbook showing a coil around a bottle of water and using the
>> earth's magnetic field! If I had played with that idea then ....
>
>I suspect that while this is *possible* it is impractical outside a nicely
>shielded lab.  The earth's magnetic field strength would likely cause too
>low a signal strength for picking anything up outside a good shielding room.

That's why you do not use the earth field, instead you swamp it using a
strong field of your own from a pm, besides the magnetisation/readout
coil. This causes the precession frequency to be higher than usual for
these instruments.

Why would anyone try to use this expensive and complex method to detect
water I don't know.

You could try to use microwave absorbtion for that, it is mucho easier,
but it depends on what kind of dirt you have.

Peter

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