Steam engine vacuum gauge, 19th century. Illustration of a front view (left) and a sectioned side view (right) of a vacuum gauge (indicator) for use in steam engines. The gauge is used to measure the vacuum in the steam engine's condenser, a critical part of the operation of the engine. This gauge runs from 0 to 76 centimetres of pressure. Artwork from 'Chaudieres et Machines a Vapeur' (1911) by French civil engineer Max de Nansouty (1854-1913), part of the 'Les merveilles de la science' series of 1867-1891 by Louis Figuier.