Henry Cavendish

French-born English scientist

• Born: October 10, 1731
• Birthplace: Nice, France
• Died: February 24, 1810
• Place of death: London, England

Cavendish, a reclusive character, made significant advances in the chemistry of gases and contributed to the study of electrical phenomena.

Early Life

Little is known in detail about the personal life of Henry Cavendish. He was born into a leading aristocratic British family. His father, Lord Charles Cavendish, was the third son of the duke of Devonshire, while his mother, Lady Anne Grey, was the daughter of the duke of Kent. His mother’s death when he was two years old left him totally in his father’s care. He entered Dr. Newcombe’s Academy in Hackney in 1742 and matriculated at St. Peter’s College, Cambridge, in 1749, leaving in 1753 without taking his degree. Most biographers have speculated that he refused the religious tests required for a degree, but no evidence exists concerning his religious convictions at any time in his life.

After leaving Cambridge, he resided with his father in London. Lord Charles Cavendish was a longtime member of the Royal Society and an avid investigator of meteorological and electrical questions, having received the society’s Copley Medal for perfecting a registering thermometer. His father sponsored his election to the Royal Society in 1760; living in an all-male environment permeated with scientific conversation may very well have shaped both Cavendish’s lifelong fascination with science and his strange social behavior.

Throughout his life, Cavendish was reclusive, shunning human society. He was restricted by his father to an extremely small allowance, forcing him to become very close with money, often attending Royal Society dinners with only the 5 shillings necessary to gain admission. Following his father’s death in 1783, he came into a large family inheritance. While very wealthy, he remained parsimonious in his personal expenditures and oddly indifferent to other uses of money, giving generously to charity but always checking the list of donors and giving precisely the amount of the largest donation. Abhorring any meeting with women—he even left notes for housemaids to avoid personal contact—Cavendish remained an eccentric and elusive person. Only in the Royal Society, where he attended regularly and participated fully, did he have any public life. He was responsible for a detailed description and analysis of the society’s meteorological instruments in 1776 and served on a committee investigating lightning protection for the Purfleet powder magazine, using his own electrical research to recommend pointed rather than blunt lightning rods. Even at the Royal Society, however, he would flee if approached by a stranger, and he was often seen outside the meeting room, waiting for the moment when he could slip in unnoticed. To the end of his life he was so totally devoted to science that everything else was secondary.

Only one portrait of Cavendish exists, a watercolor sketch by Sir John Barrow done surreptitiously at a dinner meeting of the Royal Society. It shows a somewhat tall, lanky middle-aged man of a rather sharp and thrusting appearance, dressed in a greatcoat and three-cornered hat stylish in the 1750’s. Apparently the dress was his usual, as he was noted for never changing the style of his clothing and purchased only one set of clothing at a time, following a precise schedule as the old garments were worn out.

Life’s Work

In his lifetime, Henry Cavendish was known primarily for his research in chemistry and electricity, work reflected in a remarkably small number of papers in the Philosophical Transactions of the Royal Society. His first public work was in 1776, a series of papers on the chemistry of “factitious airs,” or gases. Chemistry at the time was dominated by the idea that air was a single element, one of the four Greek elements. British chemists, from Robert Boyle, who first elucidated the gas laws in 1662, through Stephen Hales and Joseph Black in the eighteenth century, had made “pneumatic chemistry,” manipulating and measuring “air” in its various states of purity, practically a national specialty.

Chemical research was also carried on around the organizing concept of the phlogiston theory put forward by Georg Ernst Stahl in 1723. Phlogiston was the element of fire, or its principle, which caused inflammability when present in a body. It was believed to be central to most chemical reactions. Combustion was explained as a body releasing its phlogiston. In this dual context of pneumatic chemistry and phlogiston theory Cavendish presented his study of “factitious airs,” or gases contained in bodies. Most important, he isolated and identified “inflammable air,” now called hydrogen. Recognizing the explosive nature of “inflammable air,” Cavendish went on to identify it as phlogiston itself. He cannot be said to have discovered hydrogen, as others had separated it before him, and he did not specifically claim its discovery.

In 1783, Cavendish, having heard of experiments by Joseph Priestley that generated a “dew” upon exploding “inflammable air” and “common air,” presented a study of an improved eudiometer, or a device for testing the “goodness” of air. He demonstrated that “common air” was composed of constant proportions of different constituents, rather than being a single elemental substance. This research was followed the next year with two more papers on air, the research for which was principally concerned to find the cause of the absorption of gases in the eudiometer. When he mixed “inflammable air” with “common air,” he created an explosion and he noticed a dew on the containing vessel. Where Priestley had mentioned the fact in passing, Cavendish focused on it, noting that “by this experiment it appears that this dew is plain water, and consequently that almost all the inflammable air, and about one-fifth of the common air, are turned into pure water.” He had discovered that water was a compound of “airs,” not one of the four elements.

Cavendish’s priority of the discovery of the composition of water was soon disputed. He had done his experiments in the summer of 1781 but postponed publication because the resulting water was contaminated with nitric acid. Solving this problem eventually led him to his last chemical discovery, the isolation of nitric acid in 1785. He had told Priestley of his water results, and a friend had passed the same information to Antoine-Laurent Lavoisier in Paris, who repeated and extended the experiments, while James Watt also made the discovery independently. When all three published their investigations in 1784, Watt, Lavoisier, and Cavendish all laid claim to priority. A brief controversy ensued but was quickly extinguished, with each of the three rather politely deferring to the others. The controversy was rekindled in the mid-nineteenth century and continues in some scholarly circles. Cavendish should probably be conceded the right to claim the discovery of the compound nature of water, although his explanation was given in the context of the phlogiston theory. Lavoisier followed Cavendish chronologically but explained the composition of water in the radically different terms of his new antiphlogiston chemistry, as the union of oxygen and hydrogen.

Lavoisier’s antiphlogiston explanation was indicative of a revolution in chemistry that he was leading on the Continent. In 1772, when he had weighed the product of calcination (oxidation in the new terminology), there was a weight gain in the calx. He offered the explanation that something was taken up in the process, rather than phlogiston being given off. This “something” he identified as oxygen and thereby created a new chemistry. Cavendish recognized that Lavoisier’s oxygen-based chemistry was essentially equivalent to a phlogiston-based chemistry, but he rejected the new ideas to the end of his life. “It seems,” he wrote, “the phaenomena of nature might be explained very well on this principle, without the help of phlogiston; . . . but as the commonly received principle of phlogiston explains all phaenomena, at least as well as Mr. Lavoisier’s, I have adhered to that.” In 1787, Lavoisier introduced his new chemistry in his Nomenclature chimique, and fully elaborated it in 1789 in Traité élémentaire de chimie. Again Cavendish rejected the ideas, stressing that arbitrary names and ideas, as he saw them, could only lead to great mischief. By 1788, Cavendish had published the last of his chemical researches.

The second major area of Cavendish’s published research was in electrical phenomena, a near-craze sweeping through scientific and popular circles throughout Europe. In 1771, Cavendish published his first paper on electricity, putting forward a single-fluid theory of electricity, in opposition to the then popular two-fluid theory. He presented electricity as a single “fluid” that could be measured according to its compressibility, using the analogy of Boyle’s gas law. He provided a quantitative measure of tension as well as quantity, surmising that this “fluid” followed an inverse square law for repulsion, rather than the first power law displayed by gases. This work was expanded in 1776, with a paper describing his effort to construct a model of the electrical torpedo fish to analyze whether its electrical effects were similar to electrostatic phenomena, then the center of scientific attention. He demonstrated that they were the same.

In 1783, he also published a series of papers on heat, focusing on the question of the freezing point of mercury. He was able to expand upon the idea of latent heat presented earlier in the century by Joseph Black. These papers were based on a series of experiments carried out at the request of Cavendish by officers of the Hudson’s Bay Company in 1781 and after in northern Canada.

Finally, in 1798 he presented his final paper to the Royal Society, outlining his effort to measure the density of the Earth. Using an experimental torsional balance apparatus devised by John Michel, he was able to provide an extremely accurate estimate of Earth’s density, while also providing the first experimental demonstration of Sir Isaac Newton’s gravitational laws.

Significance

Henry Cavendish was widely recognized by his contemporaries as a precise experimenter and a thorough researcher, despite his small output of published works. His international reputation was certified in 1803 by election as a foreign member of the Institut de France (French Institute). This reputation was further honored in the founding of the Cavendish Society in 1846 and his family’s endowment of the Cavendish Laboratories and the Cavendish Professorship at Cambridge in 1871, where much of the fundamental research in atomic theory was carried out in the early twentieth century.

Unpublished manuscripts, discovered after his death, have significantly altered the perception of his scientific pursuits as limited solely to precise and narrow experimentation. The publication of these papers has deepened the appreciation of Cavendish’s interests and abilities. Russell McCormmach has shown that Cavendish’s work was rooted in a coherent and consistent vision of the scientific approach and theories of Newton. Newton had postulated a world made up of interacting particles, attracting and repelling one another according to strict mathematical laws. Cavendish pursued an integrated research program attempting to apply the Newtonian insight to the physical world.

Whether because he was simply shy about publishing or because he refused to publish until he was fully satisfied with the results, the world saw only a seemingly unrelated series of papers. Yet each, whether on “airs,” heat, electricity, or the density of Earth, was firmly rooted in his Newtonian vision of the world. Cavendish was the most original and creative physical theorist of his age in a nation of empirical experimenters, yet he kept his ideas hidden behind a facade of the misanthropic rejection of humanity.

Bibliography

Akroyd, Wallace Ruddell. Three Philosophers: Lavoisier, Priestley, and Cavendish. Westport, Conn.: Greenwood Press, 1970. Very readable account of the chemical revolution in relatively nontechnical terms. Focuses mainly on Lavoisier and Priestley, with a short chapter on Cavendish.

Conant, James Bryant. The Overthrow of the Phlogiston Theory: The Chemical Revolution of 1775-1789. Cambridge, Mass.: Harvard University Press, 1950. Case 2 of the Harvard Case Histories in Experimental Science series and an excellent, easily grasped, almost hands-on introduction to the experimental background of the chemical revolution.

Davis, Kenneth Sydney. The Cautionary Scientists: Priestley, Lavoisier, and the Founding of Modern Chemistry. New York: G. P. Putnam’s Sons, 1966. Relatively brief, joint biography that traces the interaction of the Scientific Revolution. Fairly popular.

Guerlac, Henry. Antoine-Laurent Lavoisier, Chemist and Revolutionary. New York: Charles Scribner’s Sons, 1975. Synthesis of a lifetime of work by the leading Lavoisier scholar. Technical and precise, yet accessible. Well worth the effort for the best understanding of the chemical revolution.

Jungnickel, Christa, and Russell McCormmach. Cavendish: The Experimental Life. Lewisburg, Pa.: Bucknell University Press, 1999. Examines Cavendish’s discoveries within the context of the elite society in which he and his father developed their scientific interests.

McCormmach, Russell. Speculative Truth: Henry Cavendish, Natural Philosophy, and the Rise of Modern Theoretical Science. New York: Oxford University Press, 2004. Explores the new theories of natural philosophy that emerged in the second half of the eighteenth century, including Cavendish’s mechanical theory of heat. Includes an edition of Cavendish’s manuscript about the mechanical theory of heat.

McKie, Douglas. Antoine Lavoisier: Scientist, Economist, Social Reformer. New York: Henry Schuman, 1952. Older, comprehensive, relatively nontechnical biography of Lavoisier that is fair in its discussion of Cavendish. Widely available in a number of paperback editions.

Miller, David Philip. Discovering Water: James Watt, Henry Cavendish, and the Nineteenth Century “Water Controversy.” Burlington, Vt.: Ashgate, 2004. Describes how Cavendish’s and Watt’s and Lavoisier’s independent discoveries that water is a compound of “airs” and not a combination of elements became an issue of controversy among nineteenth century scientists.

Wilson, George. The Life of the Honourable Henry Cavendish. London: Cavendish Society, 1851. Reprint. New York: Arno Press, 1975. A very traditional life-and-times treatment. Excessive focus on composition-of-water controversy; interesting contrast to modern treatments.