Both natural and artificial harmonics are explained and demonstrated in this film.
Natural harmonics are produced whilst bowing, with a finger of the left hand the player lightly touches the string at a nodal point. This produces a light, "fluted" sound. Notation: a small circle above the note. Artificial harmonics and produced when the string is stopped normally, and then fingered lightly (with the little finger) at a point a 4th or a 5th above the stopped note.