Musical sounds are made up of (among other things) harmonic and NonharmonicOvertones. The collection of overtones in a simple fraction-relationship (1/harmonic number) to a played pitch is called the harmonic series.
Drawbar Harmonic Interval Footage Pitch based on C2 3 Fundamental Unison 8' C2 4 2nd Harmonic Octave 4' C3 5 3rd Harmonic Twelfth 2 2/3' G3 6 4th Harmonic Fifteenth 2' C4 7 5th Harmonic Seventeenth 1 3/5' E4 8 6th Harmonic Nineteenth 1 1/3' G4 10* 7th Harmonic Flat Twenty-First 1 1/7' B-flat4, but flat 9 8th Harmonic Twenty-Second 1' C5 10* 9th Harmonic Twenty-Third 8/9' D5 11* 10th Harmonic Twenty-Fourth 4/5' E5 11th Harmonic Twenty-Fifth 8/11' F5, but sharp 11* 12th Harmonic Twenty-Sixth 2/3' G5 13th Harmonic Twenty-Seventh 8/13' A5, but flat 14th Harmonic Flat Twenty-Eighth 4/7' B-flat5, but flat 15th Harmonic Twenty-Eighth 8/15' B5 16th Harmonic Twenty-Ninth 1/2' C6
Complete list: 
http://www.organstops.org/_apps/Mutations.html.
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