On the movement of an iron particle in a magnetic field.

When moved by a magnetic field, an iron particle does not follow--quite oppositely to a widely held opinion--the field lines of the magnetic field. Rather, the force exerted onto the particle is directed towards the strongest increase of the magnetic field strength. The field lines and the force direction coincide only axially, radially they cross at an angle of 90 degrees. This has implications for ophthalmic surgery, when an extraction of iron splinters by a magnet is required.