XVII.—The Superposition of Mechanical Vibrations (Electric Oscillations) upon Magnetisation, and Conversely, in Iron, Steel, and Nickel

That mechanical vibrations affect magnetisation has long been known. The simple experiment of hammering an iron rod (Gilbert) in the earth's magnetic field needs only to be mentionedAbout twenty years ago Ewing published investigations upon the effects of vibrations on magnetism. These have been summarised in his subsequent work, Magnetic Induction in Iron and other Metals. He states (§ 84, 3rd ed.) that the “influence of vibrations and mechanical disturbances generally” “may be succinctly described by saying that vibration lessens those differences of magnetic condition to which hysteresis gives rise. Thus, if we tap a piece of iron during the application and removal of a magnetising force, we find at each stage of the application that tapping increases the susceptibility, and at each stage of the removal it reduces the retentiveness.”