Researching the life and times of Thomas Casson and the Positive Organ Company, had me looking up a back issue of 'The Organ', (Vol. 1 no. 3 p.183 January 1922). This had a section called 'Echoes from the Past,' that reprinted a Casson letter about the Swell Box from December 1888. This was annotated by someone using the pseudonym Mercurius Urbanus. Does anyone know who this referred too?