Letter from [Alan Archibald Campbell] Swinton, to Hetherington Informs that Colonel G. Thornhill has sent him drawing of a new G-cylinder internal combustion engine with sliding valves and asked his opinion of it. Explains having told Thornhill he lacks expertise in the subject and referred him to Ricardo & Co. States he has written in case Thornhill should think it worthwhile to come to Hetherington. 5 January 1928