[Dixielandjazz] Circle of 5ths

[John Farrell]

If I have understood this term correctly it means the harmonic sequence
where, for instance, C7 resolves to F, F7 to Bb, Bb7 to Eb and so on
eventually returning to the starting point. What I do not understand is why
is it known as a circle of fifths when the intervals concerned are fourths -
F is the fourth of C etc. etc.

Or have I got it completely wrong?

John Farrell
http://homepages.tesco.net/~stridepiano/midifiles.htm