Listed only by Irwin, who says: A mild String stop of 2-2/3' on the manuals, and 5-1/3' on the pedals, intended to furnish the third harmonic to the unison series in String tone. Both of these pitches in String tone are valuable. They add clarity and point to any louder flue combination, but it must be remembered their harmonics duplicate none of those of the octave-sounding stops. They are timbre creators and sources of brightness in combination, but they will slightly thicken the tone instead of making it luminous if added to any softer stops. They are String Organ Twelfths in String tone. The average Swell Organ could not tolerate such a stop, but an unusually large one could if the tone were mild, like that of an Echo Viol. The scale is determined by the brightness and loudness desired. Although narrowing the scale makes a generally softer tone, it also makes it on the brighter side, so a compromise must be reached in these two factors. It should never take the listener's attention from the unison tone. This is a stop that should not be overused, because it tires the ear and induces indifference to the music being played. The hybrid String-Diapasons are more useful than this stop, but are not so suitable in a String division. Irwin is incorrect. The harmonics of a properly tuned 2-2/3' rank (not borrowed from an octave-sounding rank) will exactly duplicate the harmonics of a open 8' rank. Harmonics are integer multiples of the fundamental frequency, and the frequency of a 2-2/3' is already the 2nd harmonic of an open 8'.