This stop is mentioned only in passing by Irwin, who says �The average Swell Organ could not tolerate [the Viol Twelfth], but an unusually large one could if the tone were mild, like that of an Echo Viol.�, and by Bonavia-Hunt, who says: �The aeoline of the modern builder is an echo viol, the scale at CC (8ft.) being approximately 2 1/2in., and at tenor C (4ft.) 1 1/2in., and in some examples smaller still.� With no description in the literature, we can only assume it to be a softer and smaller scaled version of the Viol.