1949. Seventh impression. 85 pages. Pictorial dust jacket over brown cloth. Black and white diagrams throughout. Pages remain bright and clean with minimal tanning and foxing. Binding remains firm. Minor pencil inscriptions 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. Unclipped jacket has light edge wear with minor tears, chipping and creasing. Some tanning and foxing to all surfaces, particularly to spine.