As the time line at right shows, hundreds of times in our planet's history the polarity of the magnetic shield ensheathing the globe has gone from "normal," our current orientation to the north ...

As there-could be no magic in the case, it appeared that the balance had magnetic polarity, as no other cause could produce the effect I had witnessed, and which was repeated as often as I chose ...

using a gigantic magnet, can line up the protons -- or nuclei of hydrogen atoms -- in an object (or organism) to align with the north-south polarity of the magnet. A computer "reads" this to ...