Stephen Hales Biography

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World of Anatomy and Physiology on Stephen Hales

Professionally, Stephen Hales was a clergyman, serving as "perpetual curate" of Teddington, Middlesex, England, from 1709 until his death in 1761. Avocationally, Hales was a leading scientist of his time--the founder of plant physiology, a trailblazer in the study of blood circulation and blood pressure measurement, a pioneer in public health.

Hales was born in Bekesbourne of an old Kentish family. Little is known about him until he began studies at Cambridge in 1696. At the university, Hales enthusiastically immersed himself in scientific studies and biological experiments while also pursuing his clerical degree. He received his bachelor of arts degree in 1702 and his master 's degree in 1703; he was ordained a deacon in 1703 and in 1709 he went to the "perpetual" post in Teddington.

During his early years at Teddington, Hales continued experiments which he had begun at Cambridge, achieving the first blood pressure measurements with a glass-tube manometer. He also investigated reflex actions in a decapitated frog. Hales then gave up his animal experiments, "being discouraged by the disagreeableness of anatomical dissections," and turned to the investigation of the movement of sap in plants, accidentally discovering that the force exerted by flowing sap would expand a bladder tied over a stem. From this, Hales realized he could use a glass tube, as in his animal work, to measure the force of the sap's flow.

Hales's study of plant transpiration led to his investigations of air, both "fixed" in varying substances and as given off or absorbed under different conditions, and his invention of various measuring devices. This work was tremendously important to later chemists. Another Hales contribution was the investigation of ways to chemically dissolve kidney and bladder stones, in the course of which the cleric invented a surgical forceps.

An important aspect of Hales's career was the application of his findings to practical uses. He used his knowledge of air and breathing to invent ventilators to remove noxious air from hospitals, merchant and slave ships, and prisons. He adapted a gauge from his plant experiments to ocean-depth measuring. He worked on ways to distill fresh water from ocean water. He involved himself in social issues, working for passage of the 1736 Gin Act, and was active in the founding of the colony of Georgia, while also attending to his parish duties. Noted for cheerfulness and serenity, Hales died after a brief illness and was buried at Teddington, with a monument in his memory at Westminster Abbey.