momentos: Lewis, John (1991). Great Western Auto Trailers - Part One: Pre-Grouping Vehicles. Didcot: Wild Swan. pp. 11-13. ISBN 0-906867-99-1. Kingdom, Anthony…
Horizon». Green Flash website (Sections: Astronomical Refraction, Horizon Grouping). (en inglés). San Diego State University Department of Astronomy. Archivado…
febrero de 2015. Casserley, HC; Johnston, SW (1966). Locomotives at the Grouping, Volume 4 Great Western Railway. Shepperton: Ian Allan Ltd. ISBN 0-7110-0555-9…
(March 1989). Jowett's Railway Atlas of Great Britain and Ireland: From Pre-Grouping to the Present Day (1st ed.). Sparkford: Patrick Stephens Ltd. ISBN 978-1-85260-086-0…
first herbals to a passable, stable nomenclature and somewhat reasonable grouping based on true relationships, more than 300 years of hard work were required"…