1921. Sixth edition. 243 pages. No dust jacket. Pictorial cloth covered boards. Black and white diagrams throughout. Pages with some foxing and tanning, particularly to endpapers and textblock edges. Binding remains firm. A previous owner's name to front free endpaper. Boards have heavy shelf wear with bumping and fraying to corners and crushing, fraying and tearing to spine ends and edges. All surfaces heavily tanned.