TABLE OF CONTENTS The ancient Greeks, originally those near the city of Magnesia, and also the early Chinese knew about strange and rare stones (possibly chunks of iron ore struck by lightning) with the power to attract iron. A steel needle stroked with such a lodestone became magnetic and around the year 1000 AD, the Chinese found that such a needle, when freely suspended, pointed north south.
In the late 1700s and the early 1800s, several exiting new discoveries were made in the field of Physics that paved the way for today s magnetic particle testing (MT) technology.
In the 1700s, Charles Coulomb, a French physicist, discovered that the magnetic forces of attraction and repulsion are directly proportional to the strength of the poles and inversely proportional to the square of the distance from them, (the inverse square law). He also invented the magnetoscope and magnetometer, which are devices for measuring the Earth s magnetic field strength.
Until 1821, only one kind of magnetism was known; the one produced by iron magnets. Then, Danish scientist Hans Christian Oersted, while demonstrating to friends the flow of an electric current in a wire, noticed that the current caused a nearby compass needle to move. Physicist Andre-Marie Ampere, who concluded that the nature of magnetism was quite different from what everyone had believed, studied this new phenomenon in France. It was basically a force between electric currents: two parallel currents in the same direction attract
