1955. Fourth edition. 126 pages. No dust jacket. Green cloth covered boards. Black and white photographs and diagrams. Pages remain bright and clean with minimal tanning and foxing. Binding remains firm. A previous owner's name to front free endpaper. Boards have light shelf wear with minor corner bumping and crushing to spine ends. All surfaces tanned and sunned, particularly spine. Some additional mild marks and staining. Boards are slightly bowed.