Stephen Hales was a clergyman, naturalist and inventor active in the early eighteenth century. Hales was interested in pneumatics and spent much time studying the chemistry of the air, the movement of water in plants, breathing and blood circulation. He was the first scientist to measure blood pressure.

This work contains his investigations into ventilation. As with many of the period, Hales believed that ‘bad air’ was a major cause of disease and developed a system by which fresh air could be circulated in cramped and enclosed spaces. Hales’s solution was the invention of a ventilator, essentially a set of large bellows operated by hand or by wind power that could be installed in buildings or on ships to move the air around. The ventilators were successful and reduced diseases when they were used. They also had other practical applications such as being used on the lower decks of ships to prevent dry rot and to preserve food and dry grain.