© Science Museum / Science & Society Picture Library
Made by Walter Lecuyer, Paris, of iron and bras construction. Spirometers were developed in England in the 1840s. They were used to measure the vital capacity of the lungs, that is, the largest amount of air they can hold, which indicates the health of the respiratory system. The patient's breath bubbled up a water-filled collecting drum and pushed up a sliding cylinder, which was counterbalanced by a weight. A measuring scale showed the capacity of the lungs.