| MadSci Network: Engineering |
A dip needle is the most ancient method of measuring the vertical component of the earth's magnetic field, whereas a compass measures the horizontal ones. Dip needles were once used in another abortive attempt to find longtitude by mapping just how dip angles varied around the earth. As the science of minerology has advanced many people have noticed that the earths field is distorted around mineral deposits, particularly ferromagnetic minerals obviously, like iron and nickel, but also some others. A dip needle just ain't the way to go. You need modern Ultra sensitive detectors, like a triple axis flux gate magnetometer to detect the subtle variations you need to spot. Other techniques include using a variation of nuclear magentic resonance to detect weak field and presumably they can also detect the three components of field. Measurements of ground conductance at moderate to high frequency can also yield interestting results. There have been interesting articles on building flux gate magnetometers in the British electronics journal Wireless World, now Electronics and Wireless World. WW was the magazine that Arthur C. Clarke first proposed the geostationary earth satellite. The ones you are looking for date from the late '70s-early '80s, though doubtless a little surfing should yield good results here too ! Good luck. Steve
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