Locally Measured Dip Poles

So far we have discovered four possible poles from our modeling of the full global field measurements. Expeditions to the north and south magnetic poles supposedly are searching for the locations where the main field points directly into or out of the surface. There is no concern with measurements elsewhere about the Earth. Three principal local problems affect the explorer's attempt to define this place toward which world compasses point. The first is that the explorers have local measurements...

Geomagnetism Patriarchs Gilbert

Let us pause now to talk about a few of the patriarchs of geomagnetism whose brilliant scientific contributions have brought us to our present level of magnetic field knowledge. We will start with the English physician to Queen Elizabeth I, William Gilbert (Figure 1.4), who is recognized as the father of the FIGURE 1.5 A dipole field pattern is superposed on Gilbert's picture of the Great Earth Magnet of 1600 in which he shows how magnets would naturally arrange about the surface. FIGURE 1.5 A...

Biomagnetism

Honey bees that have discovered a suitable flower patch perform a dance pattern upon returning to their hive to describe the new flower source location to their companions. Dissections show that honey bees have naturally formed FIGURE 2.17 Magnetite crystals grown by aquatic bacteria were discovered in Massachusetts by R. Blakemore. Inside these pond bacteria, the crystals form long magnets with the north pole toward their front to orient their swimming direction. FIGURE 2.17 Magnetite crystals...

Modern Field Recording

To simplify the field detection system, Gauss attached a mirror to the magnetic pointer needle axis. A ray of light directed toward the mirror cast a spot onto a far wall to allow an easier deflection measurement. It wasn't until the development of photography in the early nineteenth century that the Gauss magnetometer became a modern self-recording device. With the improved instrument in a darkened room, the light spot deflected by the mirror was directed to photographic paper attached to a...

Soda Bottle Magnetometer

Soda Bottle Magnetometer

NASA scientists have designed, for school demonstrations, a simple magnetometer (copying the Gauss variometer plan) for measuring the changes in the Earth's field.1 This soda-bottle magnetometer (Figure 5.4) is sensitive enough to detect solar-terrestrial magnetic storms. You will need Build the magnetometer by cutting the bottle in half about midway from its base. Then cut the index card so that when it is suspended inside the bottle it does not touch the sides. Glue the piece of soda straw to...

Two Eccentric Axis Poles

It became evident to early geomagneticians that not only was the Earth's dipole field tilted, it was offset from the Earth's geographic center. Two procedures have been used to find the best eccentric axis dipole location. In one, the geographic axis field IGRF coefficients were given a second special mathematical analysis that let the dipole tilt and eccentricity (the distance from the Earth geographic center) to be varied until the new dipole terms of the IGRF table were maximized at the...

Acknowledgments

This small book began during a Wednesday hiking group. Walter Page and my other nontechnical friends often asked questions about my lifelong specialty, the natural magnetic fields of the Earth. I had to find ways to explain these phenomena without equations and to answer types of questions that rarely arise from my more scientific colleagues. I so enjoyed this regular Wednesday challenge that this book developed quite easily. Although most illustrations are of my own creation, I thank the many...

Solar Quiet Sq

Ionospheric Dynamo

The 100-km-high ionospheric current is given the name solar quiet-day variations (Sq). Such current is responsible for the recurring regular form of the daytime field variations seen at world observatories, typically 10 to 30 gammas for mid-latitudes. Seasonal changes in both the ionospheric conductivity, the wind system within the ionosphere, and the atmospheric expansion or contraction cause seasonal changes in the Sq current. As you might guess, there is also a lunar quiet-day ionospheric...

Magnetic Fields and Technology Destruction in Space

Soda Bottle Magnetometer

Geomagnetic storms are natural magnetic field changes caused by processes that start on the Sun. An onrush of high-energy charged solar particles and fields temporarily disrupts the magnetosphere region of man-made Earth satellites (Figure 2.19). In March 2000, NASA launched a special IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) spacecraft to explore and monitor this region. Space weather forecasting has become a major program for modern nations. We defer our detailed look at...

Modeling

Fifth, when a true relationship is found, scientists concern themselves with the reason for such established connections between phenomena and, for ingested chemicals, whether there are attending unwanted side effects . Models of the biological, physical, and chemical processes are examined for an explanation of the relationship so that its full understanding can become a useful part of world knowledge. Scientists try to determine if the correlated phenomena are in a cause-and-effect...

Pseudoscience Old Wives Tales and Frauds Magnetic Termites

Although bees respond to fields, magnetic sensing has been falsely ascribed to other insects. One of these is a special breed of magnetic termites that exists in tropical northern Australia and is restricted to small areas just south of Darwin, at Arnhem Land, and at the Cape York peninsula. These termites are named for their construction of clusters of 100 or more tombstone-like mounds up to 6 ft 2 meters tall, oriented with their long axis aligned approximately 10 east of a geographic...

Water Witching or Divining

The universal tool of almost all water witches or diviners, who profess to have the ability to locate groundwater, is a wooden branch or a metal wire rod often a wire coat-hanger , shaped either like a large letter Y or L, called a divining rod. Held tightly in the hands of the witch, the pointing end is said to be magnetically pulled down toward the region of the ground where the desired water is located Figure 2.33 . The search is usually for a waterwell site or a location of buried water...