What are Harmonics?
Harmonics on the violin are played by lightly touching the string instead of pressing it all the way down to the fingerboard. The sound created is much higher in pitch than if the string were pressed down. It is usually a very pretty, ringing sound and is sometimes used in classical music.How Do They Work?
Harmonics are created by a standing wave in the string that has a shorter period than the regularly played note. The period of the harmonic is often 4 times shorter than the length of the whole string. The position of the lightly touched finger serves as a node for the standing wave, which means that the pitch of the harmonic can also be changed depending on the position of the finger. However, not all finger positions will have a harmonic because the period of the harmonic must evenly divide over the length of the string.
http://newt.phys.unsw.edu.au/jw/strings.html
In the figure above λ1 is the original wavelength and L is the length of the string. λ2, λ3 and λ4 are all possible harmonics with different node positions.
In the figure above λ1 is the original wavelength and L is the length of the string. λ2, λ3 and λ4 are all possible harmonics with different node positions.