Following on from the previous lesson.
If you divide the open bottom E string into 3 parts you get the note B [ B3 ].
These thirds of a string length are found at the 7th fret and the 19th fret (both positions give exactly the same harmonic) — the fretted notes at these positions also happen to be B.
If you sub-divide to a 6th of a string length — i.e exactly halfway between the nut and the 7th fret — fret 3 and a bit, you get B an octave higher [ B4 ].
Go on to the next lesson for more Natural Harmonics