The Harmonic Series

2' PITCH (the fourth partial)

As the string continues to vibrate in this complex way, it also vibrates in fourths, producing the fifteenth, the C two octaves above tenor C. This is the fourth partial or harmonic, and the third overtone.

If you were to play tenor C at the organ and pull a 2-foot stop only, you would hear the fifteenth, the C two octaves above tenor C.

2' stops are octave-sounding stops, which sound the note at some octave above or below the key being played.