The higher the note, the faster the string vibrates. An A above middle C (the violinist’s A string) vibrates at 440Hz (440 times per second). This is the “fundamental” or “first harmonic”. The second harmonic vibrates twice as fast (ratio 2:1): 880Hz. This gives an A an octave higher. The third harmonic will give a ratio 3:2. This will be an E (an octave and a fifth above the fundamental). The higher the harmonic the quieter it is, but the ratio is always a whole number (not a fraction).