An 8' Diapason whose pipes are double-length, overblown to speak the first harmonic. The pipes are of normal length below middle c or tenor G. The earliest use of this stop, as mentioned in the literature, is by the Bryceson Brothers, organ builders of London, England, in the second half of the 19th century. The harmonic treatment dulls the tone to the point where it is no longer really a Diapason, and is not suitable for supporting a Diapason chorus. Neither Audsley not Wedgwood speak highly of it.
Harmonic Diapason (8'?); Concert Hall, Paisley, Scotland; Bryceson Brothers, 1882.