http://books.google.co.uk/books?id=cAgLx-BHY80C&pg=PA279&lpg=PA279&dq=Bicycles+and+Tricycles+-An+Elementary+Treatise+on+their+Design+and+Construction&source=web&ots=OOsKjKA5ag&sig=31sLxw7c1bRIY7 cB6YFeVE_9T9E&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA292,M1