这本书是有关于地磁的.This book is about the earth's magnetism.他们发现, 牛在吃草或是休息的时候, 总是面向地磁的南极或是北极.And, when grazing or resting, cows tended to face either magnetic north or south....

“地磁的”的英语可以翻译为：geomagnetic ...