Harmonics are higher pitched notes that are created when a vibrating string or column of air vibrates along its whole length and a subdivision of its length. On string instruments, they are created by lightly touching the string at a precise mathematical point; for example, precisely halfway along the A string will produce an A an octave higher, and if you touch the A string one quarter of the way along, it will produce an A two octaves higher!
A wind or brass instrument can produce these notes that are higher than the full-length of the instrument (the fundamental) by blowing harder, and this is an important element of learning to play a brass instrument. Harmonics can sound much purer than other notes, especially on stringed instruments. Did you know, composers often use them to create special effects in their music. If you play a string instrument, you could experiment by lightly running your finger up and down the string whilst bowing, or bowing harder and harder until you hear a wonderful collection of all your instrument’s harmonics!