We will refer to the field, through which the interaction of electric currents, located at a distance, magnetic field. Experience has shown, that magnetic field creates a moving electric charges or variable electric field acts only on moving charges. So, to detect magnetic field in any region of space, you need to make in the area of the conductor or any other moving charges. First magnetic field around conductors with currents empirically discovered Danish physicist G. Oersted in 1820 g.

Magnetic fields of different currents in the superposition can be constructive, and weaken each other. Let us illustrate this by the experience. If you link together two identical coils and create in them currents of opposite directions (rice. 22.2, and to the left), the total field is so weak, that won't produce noticeable steps on third coil with a current. This explains, why is there no magnetic field around the cord, woven from two wires with currents in opposite directions. If the coils connected to generate currents of the same direction, their effect on third coil with a current is considerably improved (rice. 22.2, b) compared to experience, described in the previous paragraph. So, the magnetic field amplification can be obtained by applying a magnetic field currents of identical directions, and the weakening of the field — overlay field currents of opposite directions.

If the coil before the experiment to have so, so that their axes were not on the same line, when the power of their current coils themselves rotate so, the currents in them are flowing in the same direction, and then are attracted to each other. As a result, the magnetic field in the surrounding space increases.