every note that is played on an instrument is really a combination of several notes or “harmonics”, even though we may not realize that we are hearing more than one note at a time. play the lowest c on the piano. now find the next c which is an octave higher. press this key very slowly so that it does not sound and hold it down. while holding it down play the bottom c again making it loud and very short. the c that is being held silently will now sound. this is because the strings of that c are vibrating a little because it is a harmonic of the low c (they can vibrate because the damper is off the string while the note is being held down). the same can be done holding the next g down, then the next c, then the e. the higher the note the fainter (quieter) the harmonics become. the musical example below shows the notes of a harmonic series in musical notation.