1822, French physicist Arago and Lussac found that when the current through the winding of which iron, it can be the iron magnetization. This is actually a wet solenoid valve principle first discovered.
In 1823, Sturgeon also made a similar experiment: he is not in a U-shaped iron bar magnet stick around for 18 laps on the copper wires, copper wire and voltaic cell when switched on, around the U iron bar type copper coils that generate the intense magnetic field, thus making a U-shaped iron bar into a "wet solenoids." This wet solenoid valve on the magnetic energy than the large permanent magnet to put times, it can pick up more than 20 times its weight of iron, and when the power is cut off, U-shaped iron bar on what iron is unable to absorb again become an ordinary iron bar.
Linear current amp is set on a short straight line current is also applied. Ring current can be seen as composed of many small pieces of line currents, each with a short straight line current in amperes current setting is to determine the ring current magnetic induction on the central axis direction.
Stacking up to get the ring current magnetic induction on the central axis line direction, Linear current amp is a basic set, you can set the ring current amp current amps set by the straight line is a straight line to export the current amp is set for the linear movement of the charge also applies to the magnetic field, when the current direction and direction of movement of positive charge the same, with the negative charge movement in the opposite direction.
Oster magnetic effect in the current series of experiments and other experiments, inspired by the amps recognize the nature of current magnetic phenomena, involving current and magnetic current attributed to a variety of interactions between the interaction, look for the current proposed per the law of interaction of basic questions. In order to overcome the current element can not be directly measured in isolation difficulties, amps designed four experiments show zero, and accompanied by careful theoretical analysis, the results obtained. However, due to the electromagnetic effects amp hold the concept of action at a distance, was imposed in the theoretical analysis of two current element along the connection between the forces of assumptions, expectations follow Newton's third law, the conclusion is wrong. The formula is wrong to abandon the assumption that the force along the connection, the amended results. Short-range effects should be understood as a point of view, the current per magnetic field, magnetic field on which the current element subjected to another force.