distinct sound resulting from absence of the damping action of a finger, and from the fact that vibrato (see below) is produced differently from on fingered notes. Other than low G (which can be played in no other way), open strings are sometimes selected for special effects. One striking effect that employs open strings is bariolage. This is the repeated alternation of notes played on two or more strings, where one of the notes is usually an open string. This string crossing is often rapid, and is best executed with a sinuous movement of the bow arm. Sometimes the same pitch as an open string will be fingered on an adjacent string, so that the alternation is between the same note on two strings, one stopped, one open, giving a rhythmic pulsating effect. Bariolage was a favorite device of Joseph Haydn, who used it for example in his string quartet Opus 50 no. 6, and in the "Farewell" Symphony. It is also prominently featured in the Preludium of Bach's Partita No.3 in E major for solo violin. Playing an open string simultaneously with a stopped note on an adjacent string produces a bagpipe-like drone, often used by composers in imitation of folk music. Sometimes the two notes are identical (for instance, playing a fingered A on the D string against the open A string), giving a ringing sort of "fiddling" sound. Double stops and drones Double stopping is when stopped notes are played on two adjacent strings, producing a two-note harmony. This is more difficult than normal single-string playing, as fingers must be accurately placed on two strings simultaneously. Sometimes moving to a higher position is necessary for the left hand to be able to reach both notes at once. Double stopping is also used to mean playing on three or all four strings at once, although such practices are more properly called triple or quadruple stopping. Collectively, double, triple and quadruple stopping is called multiple stopping. However, triple or quadruple stopping is more commonly just called a chord. Sounding an open string alongside a fingered note is another way to get a harmony. While sometimes also called a double stop, it is more properly called a drone, as the drone note (the open string) may be sustained for a passage of different notes played on the adjacent string. Vibrato Vibrato is a technique of the left hand and arm