The English scientist and clergyman Stephen Hales (1677-1761) pioneered the study of plant physiology, contributed the first major account of blood pressure, and invented a machine for ventilating buildings.

Stephen Hales was born in Bekesbourne, Kent, on September 17, 1677. He entered Corpus Christi College, Cambridge, in 1697, where he studied theology and took a degree in arts in 1703. He received his doctorate from Cambridge in 1733. At Cambridge, Hales was caught up in the backwash of Isaac Newton's great work at the university, and he acquired an interest in astronomy, physics, and chemistry as well as in biology. In 1708 Hales became perpetual curate of Teddington in Middlesex, and here he remained until his death. In 1719 he married Mary Newce, who died two years later without issue.

In 1711 Hales began his studies on blood pressure. True to his mechanistic views, he carefully measured the blood pressure of three horses and produced the...