In her debut, Turner (Geophysics/Victoria Univ., New Zealand) negotiates the slippery ground between hard and popular science in this story of magnetism.
The author begins with the ancient Greeks, as well as the Chinese, who used the compass in the art of feng shui, and continues through its deployment by Europeans (who may have independently discovered the tool) in the creation of portolan charts and rhumb lines, which allowed mariners to move beyond known coastlines. Despite these advances, the idea of magnetism was still little-understood. Enter the physicists and mathematicians, and here Turner takes no prisoners in her popular audience. To appreciate that the Earth’s magnetic field is a “geocentric axial dipole,” readers will have to dig through discussions of physics, chemistry, electricity, precession, nutation, perturbation, seismology and the Chandler wobble. Some of the author’s knottier sentences—e.g., “the ratios of rough measurements of magnetic field strength (or, more precisely, dipole moment) and rotational angular momentum came very close to the square root of the gravitational constant—the constant, G, in Newton’s law of gravitation, which had eventually been measured by Henry Cavendish—divided by the speed of light”—may be a bit much for general readers, but for the most part Turner achieves an engaging appreciation of science at work discovering the mysteries of magnetism. By the time she hits continental drift, polar wander and the geodynamo theory, readers may even understand what she means by saying that “the twisting and shearing caused by convection and the rotation of the Earth convert toroidal field lines into poloidal field lines and vice versa.”
A mostly smooth explanation of a rarefied area of science.