From the website:
"A photograph of a sentry outside Wellington Barracks, London, dressed in a full chemical protection suit and a gas mask, taken by Sayers for the Daily Herald newspaper on 10 February, 1938. The sentry was taking part in an air raid precautions exercise. A piece of specially-treated paper is attached to his bayonet. This acts as a detector which changes colour when gas is present, enabling the sentry to raise the alarm. The man in the background is a newsreel photographer who is carrying a cine camera. This photograph has been selected from the Daily Herald Archive, a collection of over three million photographs. The archive holds work of international, national and local importance by both staff and agency photographers."
Read more reflections on history, idleness, and the art of living from the Idle Historian in To The Idler The Spoils