Bricks, mortar and magnetism

Medieval French castle, churches yield new data about field changes

TORONTO — New analyses of bricks and mortar from French buildings constructed during the 9th and 10th centuries are providing information about Earth’s magnetic field at the time, Annick Chauvin, a geophysicist at the University of Rennes 1 in France, and her colleagues reported May 25 at a meeting of the American Geophysical Union.