Take a magnetic needle NS, which can rotate freely about a vertical axis in horizontal plane. Hold a conducting wire AB over the magnetic needle NS parallel to it. Complete the circuit by closing the key such that current flows from A to B.
It is found that N-pole of the magnetic needle gets deflected the west. If the direction of current in the wire is reversed (i.e. from B to A), the N-pole of magnetic needle gets deflected towards east. Since magnetic needle can be deflected by another magnetic field therefore current in the wire must be producing a magnetic field in the surrounding space.