'The Periscope in the Trenches', (1919). Scene from the First World War, 1914-1919: 'The eye of the submarine has been pressed into service on land: by its use observation can be made with comparative safety. The periscope consists of a long, hollow box or tube, at either end of which is fixed a mirror so adjusted as to reflect the view in front of the trench to the eye of the observer.' From "The History of the Great European War: its causes and effects", Vol. III, by W. Stanley Macbean Knight. [Caxton Pulishing Company, Limited, London, 1919]