Stephen Hales
1677-1761
English Physiologist and Clergyman
Although trained as a clergyman with no formal education in physiology, chemistry, or medicine, Stephen Hales became one of the most important British scientists of the eighteenth century. He can be considered the father of plant physiology, and his studies of circulation in animals were the most important after William Harvey's (1578-1657) over a century earlier. Hales conducted experiments on gases with equipment of his own design that influenced the later work of Joseph Black (1728-1799),Henry Cavendish (1731-1810), Joseph Priestley (1733-1804), and Antoine Lavoisier (1743-1794). He also did important research on respiration and in public health involving ventilation and fresh air.
Stephen Hales was born in Bekesbourne, county of Kent, England, on September 17, 1677, into an established, influential family. In 1696 he entered Benet College at Cambridge University, where he received a bachelor's degree and then a master's in 1703. In 1709 he was ordained as a priest in the Anglican Church and left Cambridge to become minister at Teddington, a small town on the Thames River between Twickenham and Hampton Court and about 15 miles (24 km) west of London. Hales kept this religious post until his death in January 1761, and did most of his research work at Teddington.
While at Cambridge Hales gained his first knowledge of scientific experimentation. In 1703 William Stukeley, later to become a well-known London physician, entered Benet College; and he and Hales developed a close friendship. In a room provided by Stukeley's tutor, the young men set up a laboratory where they conducted chemistry experiments and dissected small animals, including frogs. By 1707 Hales was attempting to measure blood flow in dogs. In these years before he left Cambridge, Hales also attended chemistry lectures by John Francis Vigani and his successor, John Waller.
After taking his religious post at Teddington, Hales spent several years attending to his parish duties before renewing his interest in science. By 1714 Hales began a study of the force of circulating blood—what we call blood pressure—in larger animals such as horses and deer. In 1719 he turned his attention to a study of the force of sap in plants. By this time Hales had been nominated to a fellowship in the Royal Society, a prestigious honor that validated his efforts. Membership in this body meant that oral accounts of Hales's research presented at the Society's meetings would be heard by the most important scientists and physicians in Britain at that time. Finally, Hales began to publish his work; in 1727 his book Vegetable Staticks; Or, an Account of Some Statical Experiments on the Sap in Vegetables was published in London. In 1733 Haemastaticks; Or, an Account of Some Hydraulic and Hydrostatical Experiments Made on the Blood and Blood-Vessels of Animals appeared.
These two works described in great detail Hales's meticulous experiments, which were characterized by his close observation and measurement. His most famous experiment is described in the first few pages of Haemastaticks. Hales tied down a horse and cut open an artery about three inches from the stomach. Into this artery he inserted a brass pipe only 0.167 inch (0.424 cm) in diameter. Then he used another brass tube fitted to the first one to attach a glass tube 9 feet (2.74 m) in length. Hales could then watch the mare's blood rise with each heartbeat over 8 feet (2.43 m) into the glass pipe. After these measurements Hales removed the glass tube and measured the blood released until the horse died. Then he studied the heart and surrounding arteries to see how much blood remained in the carcass. Hales repeated these experiments in cows, deer, dogs, and sheep, and carefully recorded the results. He also conducted other experiments to detect the flow of blood through the lungs; in describing the tiny blood vessels in the lungs, Hales was apparently the first person to use the term "capillary." Hales demonstrated the same curiosity and attention to detail in his studies of sap and water flow in plants; he invented the U-tube manometer to aid him in this research.
Between 1725 and 1727 Hales conducted important research on gases. In his plant experiments Hales had noticed bubbles of air that appeared when a plant stem was cut. Hales developed several apparatuses that would allow him to measure the amount of air absorbed or released when various animal, plant, or chemical compounds were heated and cooled. His most famous device was the pneumatic trough, with which he could collect different gases. Although Hales did not differentiate one gas from another, this research and the pneumatic trough became very useful to later chemists who did manage to isolate the various gases.
In 1739 Hales received the Copley Prize from the Royal Society, which recognized the importance of his scientific work. Six years earlier he had been awarded the Doctor of Divinity degree from Cambridge. In the 1750s Hales helped develop a channel and drainage system that supplied Teddington with fresh water. He was also interested in the problem of fresh air in confined spaces such as ships, hospitals, and prisons, and he developed a ventilator and bellows system to supply fresh air in these areas. His ventilation systems were installed in British navy warships and in several prisons, including the notorious Newgate. Hales's ventilators did not remove bacteria, which were unknown at the time, but mortality among the sailors and prisoners was reduced. In addition to his clericalduties and his scientific researches, Hales also served as one of the original trustees of the American colony of Georgia. Although he never visited America, Hales left his entire library to the colonies in his will. Unfortunately, the books disappeared and have never been located.
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