Twenty-Third is listed only by Irwin, who gives the following description: A rank of open metal Foundation pipes at 8/9' on the manuals, and 1 7/9' on the pedals. It sounds the notes three octaves and one note above the keys struck, at D5 from middle C key, and D1 from the pedal low CCC key. It is roughly in the position of the ninth harmonic of the unison series (on both manuals and pedals). It is a somewhat undiscovered source of brillianct, cymbal-like brassiness on organs. In actual practice it is seen as a small-scale, soft Diapason or Geigen Diapason. It could be a Dulciana as well. Irwin is incorrect. A properly tuned 8/9' rank will speak at exactly the ninth harmonic, and sound only very roughly a D when played from a C key. Elswhere Irwin gives None as a synonym.Neuvième is listed only by Sumner, who says: �None. A mutation stop of 8/9-ft. pitch.�
Osiris contains over two dozen examples of None, all at 8/9' pitch except for one at 4/9'; five examples of Neuvième, three at 1 7/9' and two at 8/9'; and a single example of Twenty-Third. With the exception of the Atlantic City organ, we know of no examples prior to the 1950's, and many examples date from the 1960's.