Book excerpt: Ship Magnetism and the Magnetic Compass deals with the magnetism of ships and the deviation of the magnetic compass produced by this magnetism. Emphasis is placed on the distinction between the deviation itself and what causes the deviation. Numerous worked examples for exercise are found at the end of each chapter. Comprised of 15 chapters, this volume begins with an introduction to magnetometry, paying particular attention to the magnitude of the forces involved in magnetism and the manner in which these forces act. The strength of a magnetic pole is also considered, along with the angle of deflection of the needle when in two magnetic fields. Subsequent chapters offer a thorough treatment of the strength of the magnetic field and the magnet's moment of inertia and magnetic moment; the earth's magnetic force; and how the different parts of the ship's magnetic force give different types of deviation. The book also explains the heeling error and its causes; the principle underlying successful compass adjustment; the effect of the ship's magnetic forces on the directive force felt by the compass needles; and sub-permanent magnetism. This monograph will be of value to students and practitioners interested in ship magnetism and the magnetic compass.