Cavendish, Henry

(b. Nice, France, 10 October 1731; d. London, England, 24 February 1810),

natural philosophy.

In an age when leading British scientists were largely middle-class, Henry Cavendish stood out for his high aristocratic lineage. Although without title (he was, however, often addressed by the courtesy title “Honourable”), he was descended from dukes on both sides. His father. Lord Charles Cavendish, was the fifth son of the second duke of Devonshire. His mother, formerly Lady Anne Grey, was the fourth daughter of the duke of Kent. His mother’s health was poor, for which reason she went to Nice, where Henry was born. She died two years later, shortly after giving birth to her second son, Frederick.

At eleven Cavendish was sent to Dr. Newcome’s Academy at Hackney, a school attended mainly by children of the upper classes. He proceeded to St. Peter’s College, Cambridge, in 1749, entering as a Fellow Commoner. He remained at Cambridge until 1753, leaving without a degree, a practice frequent among Fellow Commoners. It has been suggested that Cavendish objected to the religious tests at Cambridge, but in fact nothing is known about his religious convictions or lack of them. After leaving Cambridge he lived with his father in Great Marlborough Street. London, where he fitted out a laboratory and workshop. When his father died in 1783, Cavendish transferred his main residence and laboratory to Clapham Common. He never married.

Cavendish had independent means all of his life and never had to prepare for a profession; at some point he became immensely wealthy through bequests from relatives. At no time did he show an interest in entering the nonscientific world open to one with his assets of wealth and class. He shunned conventional society, which, by all contemporary accounts, he found difficult. Instead he devoted himself almost exclusively to scientific pursuits. His father, a distinguished experimentalist and prominent figure in the counsels of the Royal Society, encouraged his scientific bent. He put his instruments at his son’s disposal and, most important, introduced him into London’s scientific circles. In 1758 he took Henry to meetings of the Royal Society and to dinners of the Royal Society Club. Henry was elected to membership in these organizations in 1760, and he rarely missed a meeting.

Like his father, Cavendish was heavily involved in the work of the Council and committees of the Royal Society. He was a member of the Royal Society of Arts (1760) and a fellow of the Society of Antiquaries (1773). He was a trustee of the British Museum (1773) and a manager of the Royal Institution (1800). His career in general was distinguished by a wide and usually active participation in the organized scientific and intellectual life of London. Toward the latter part of his career he was esteemed at home and abroad (he was elected foreign associate of the Institut de France) as the most distinguished British man of science.

Henry Cavendish had fitful habits of publication that did not at all reveal the universal scope of his natural philosophy. He wrote no books and fewer than twenty articles in a career of nearly fifty years. Only one major paper was theoretical, a study of electricity in 1771; the remainder of his major papers were carefully delimited experimental inquiries, the most important of which were those on pneumatic chemistry in 1766 and 1783–1788, on freezing temperatures in 1783–1788, and on the density of the earth in 1798. The voluminous manuscripts uncovered after his death show that he carried on experimental, observational, and mathematical researches in literally all of the physical sciences of his day. They correct the impression derived from his few published writings that his interests were predominantly experimental and chemical.

Many of his interests—pure mathematics, mechanics, optics, magnetism, geology, and industrial science—that are strongly represented in his private papers are barely reflected in his published works. Cavendish left unpublished whatever did not fully satisfy him, and that included the great majority of his researches. The profundity of his private studies has exercised an immense fascination on subsequent workers in the fields that Cavendish explored. Fragments of his unpublished work were gradually revealed throughout the nineteenth century, culminating in James Clerk Maxwell’s great edition of Cavendish’s electrical researches in 1879. Far less successful was the attempt in 1921 by a group of scientific specialists to select for publication certain of Cavendish’s nonelectrical manuscripts to complement Maxwell’s edition. The totality of Cavendish’s researches was too vast for that design.

The unifying ideas underlying Cavendish’s numerous and varied basic researches relate to the Newtonian framework in which he chose to work. While he drew immediate stimulus from his contemporaries, the ultimate source of his inspiration was Newton. In the preface to the principia, after explaining how he had derived the law of gravitation from astronomical phenomena and how he had deduced from it the motions of the planets, comets, and the seas, Newton expressed his wish that the rest of nature could be derived from the attracting and repelling forces of particles and the results cast in the deductive mode of the Principia. It was the conception of natural philosophy as the search for the forces of particles that guided Cavendish’s scientific explorations. (His one important difference with Newton was his preference for the point–particles of John Michell and Bošković over Newton’s extended corpuscles.) The Principia was forever his model of exact science; when this fact is appreciated, his various and seemingly disconnected researches are seen to form a rational, coherent whole.

Little is known about Cavendish’s scientific activities between his leaving Cambridge and his first publication in 1766. His extant manuscripts suggest that he devoted much early effort to dynamics. The most important dynamical study. “Remarks Relating to the Theory of Motion,” contains a full statement of his theory of heat, he subscribed to Newton’s view that heat is the vibration of particles but went beyond Newton in rendering the vibration theory precise: Heat, Cavendish said, is the “mechanical momentum.” or via viva, of vibrating particles. He proved that the time average of the mechanical momentum of a collection of particles remains sensibly constant, provided the forces have certain symmetry properties. He related this theorem to another conservation law. It was well known that when two bodies are placed in thermal contact, the heal lost by one equals that gained by the other. Cavendish interpreted this to mean that the mechanical momentum lost by the particles of one body equals that gained by the particles of the second. But he was not satisfied. He had observed phenomena—such as fermentation, dissolution, and combustion—that involve quantities of heat which are inexplicable, even when the “additional” mechanical momentum of elastic compression is taken into account. Cavendish turned to heat experiments, which indicated a way around the theoretical impasse.

Cavendish drafted in fair copy, but did not publish, a long manuscript entitled “Experiments on Heat.” based on laboratory work done in and possibly before 1765. Although he knew something of the work of Joseph Black and his circle, he essentially rediscovered the basic facts of specific heats (a term he later privately endorsed) and latent heats (a term he also privately endorsed but only after divorcing it from its connotation of a material theory of heat). The difference in specific heats of mixtures or compounds and their component parts helped him explain the anomalous heats in the reactions violating his Newtonian heat theory. He thought that the difference in the specific heats accounted entirely for the addition or subtraction of sensible heat in reactions. Cavendish broke off his accounts of both specific and latent heats with inconclusive experiments on airs. In the one case he tried to find the specific heat of air by passing it through a worm tube encased in hot water, measuring the increase in the heat of the air. In the other he measured the cold produced by dissolving alkaline substances in acids, releasing fixed air, a phenomenon that he viewed as similar to evaporation.

In 1766 Cavendish published his first paper, for which he received the Royal Society’s Copley Medal. It was on “factitious” airs, that is, airs that are contained inelastically in other bodies but are capable of being freed and made elastic. Cavendish’s careful gravimetric discrimination of several factitious airs, together with the work of Black on fixed air, put forward strong evidence against the notion of a single, universal air. Cavendish produced fixed air by dissolving alkaline substances in acids, and by dissolving metals in acids he released inflammable air. He collected the airs that animal and vegetable substances yield on putrefaction and fermentation. (These agents—metals, alkalies, animal and vegetable matter— and their associated airs were the ones that Cavendish treated in the context of his last heat experiments.) He collected airs by inverting a bottle filled with water (or mercury for water-soluble fixed air) in a trough of water (or mercury): a tube led from the mouth of the inverted bottle to another, in which the reactants were placed. After collecting the airs he observed their combustibility, water solubility, and specific gravity. He found that fixed air is 1.57 times heavier than common air and that inflammable air is about eleven times lighter than common air. He showed that fermented organic substances give off a mixture of airs which includes a heavier inflammable air, from the fact that the same weight of a metal (zinc, iron, tin) produced the same volume of inflammable air regardless of the acid used (diluted sulfuric or hydrochloric acid), cavendish concluded that the inflammable air came from the metal, not the acid. He suggested that the inflammable air of metals is pure phlogiston. In 1767 he published a related study of the composition of water from a certain pump, proving that the calcareous earth in the water is held in solution by fixed air.

In 1771, guided by his knowledge of elastic airs, Cavendish published a mathematical, single-fluid theory of electricity. In a preliminary draft he introduced the term “compression” in speaking of the state of tension of the electric fluid. Although he omitted the expression from his published theory, he retained the notion that the electric fluid within a body resembles an air compressed in a container. This was the central idea of his theory, providing an intensity measure in addition to a quantity measure of the electric fluid. There were essential differences, too, between the elastic fluids of electricity and air; and Cavendish stressed these as well as their resemblances. He proved that the particles of the electric fluid did not follow Newton’s inverse first-power law of force of air particles. Just as his experimental discrimination among factitious airs helped discredit the notion that there is only one true, permanent air, so his electrical investigations indicated that, contrary to the common belief, there are elastic fluids in nature which must be represented by different laws of force. Cavendish was able to mathematize fully only one elastic fluid, that of electricity; elastic airs proved too complex.

Joseph Priestley, having stated the inverse-square law for the electric force in 1767, may have provided the occasion for Cavendish to elaborate his ideas on electricity. From the beginning Cavendish was partial to the inverse-square law, although in 1771 he had not yet performed his now famous hollow-globe experiments to settle the question of the exact numerical power. He postulated instead an elastic, electric matter of electricity, the particles of which repel one another and attract the particles of all other matter with a force varying inversely as some power of the distance less than the cube; in a symmetric manner the particles of all other matter repel each other and attract those of the electric fluid according to the same law. Cavendish’s object was to exhibit the consequences of a variety of long-range electric forces and then to select the actual law from all possible laws by comparing their consequences with experience. His electrical researches are a direct expression, and partial vindication, of Newton’s vision of the future of natural philosophy. From certain phenomena Cavendish deduced, but did not publish, the exact law of electric attraction and repulsion between particles; and from that law he derived a rich store of new, quantitative electrical phenomena. His greatest predictive achievement lay buried in manuscript: it was the calculation and experimental confirmation of the precise quantities of electric fluid that bodies of different geometrical form and size can contain at any electrical tension. His confirmatory experiments, together with an extended theoretical development, constituted the design of an unfinished, unpublished treatise, a work that was intended to stand as the electrical sequel to the gravitational “System of the World” of the Principia.

Cavendish examined minutely the facts of specific inductive capacity (not his term), an electrical corollary of chemical differences. His efforts at understanding this empirical phenomenon, which seemed at first to contradict his theory, diverted him from completing his original design. So did the fact that he came to seek a dynamics as well as a statics of the electric fluid. He attempted without success to find the relation between force, resistance, and velocity in the passage of the electric fluid through various substances. His researches trailed off into largely inconclusive experiments on conductivities. He revealed certain of his dynamical findings in a second electrical publication, a study in 1776 of the properties of a model of an electric fish, the torpedo. His electrical researches, the most sustained and organized effort of his career, came to an end in 1781.

Priestley’s account in 1781 of his and John Warltire’s experiments prompted Cavendish to return to the subject of elastic airs. The first of his new publications on the subject was a study of the principles of eudiometry in 1783. The most important fruit of his renewed interest was his celebrated publication in 1784 on the synthesis of water from two airs. Warltire had electrically fired mixtures of common and inflammable airs in a closed vessel, recording a weight loss that he attributed to the escape of ponderable heat. He and Priestley observed a deposit of dew inside the vessel.

Cavendish repeated the experiments and found dew but no loss in weight. He then undertook experiments to discover the cause of the diminution of common air when it is fired with inflammable air and when it is phlogisticated by any other means. He found that when inflammable and common air are exploded, all of the inflammable air and about four-fifths of the common air are converted into dew and that this dew is pure water. What Cavendish was basically interested in was the constitution of the airs; he concluded that inflammable air is phlogiston united to water and that dephlogisticated air is water deprived of phlogiston. In several papers through 1788 he pursued investigations stemming from those of 1784, concluding that phlogisticated air is nitrous acid united to phlogiston. Cavendish’s publications on pneumatic chemistry in 1783–1788 involved the agency of electricity, the transition between elastic and inelastic states of matter, and the generation of heat; they drew, therefore, on the basic themes of his research for the previous quarter century.

Concurrently with his work on airs Cavendish published several papers on the freezing points of mercury, vitriolic acid, nitrous acid, and other liquids. This work was an extension of his published study of the Royal Society’s meteorological instruments in 1776, and it drew heavily upon his early knowledge of latent heats. The most important of his conclusions was that the extraordinarily low readings that had been recorded on mercury thermometers were due merely to the shrinkage of solidifying mercury.

Cavendish published five papers between 1784 and 1809 relating to his astronomical interests. With one exception they were comparatively minor productions, concerned with the height of the aurora, a reconstruction of the Hindu civil year, a calculation in nautical astronomy, and a method of marking divisions on circular astronomical instruments. The exception was his determination of the density of the earth (or weighing of the world) in 1798, by means of John Michell’s torsion balance. The apparatus consisted of two lead balls on either end of a suspended beam; these movable balls were attracted by a pair of stationary lead balls. Cavendish calculated the force of attraction between the balls from the observed period of oscillation of the balance and deduced the density of the earth from the force. He found it to be 5.48 times that of water. Cavendish was the first to observe gravitational motions induced by comparatively minute portions of ordinary matter. The attractions that he measured were unprecedentedly small, being only 1/500,000,000 times as great as the weight of the bodies. By weighing the world he rendered the law of gravitation complete. The law was no longer a proportionality statement but a quantitatively exact one; this was the most important addition to the science of gravitation since Newton.

Cavendish’s career marked the culmination and the end of the original British tradition in mathematical physics. By the 1780’s, British natural philosophy had moved away from any central concern with mathematical interparticulate forces. It had become concerned with the ethereal mode of communication of forces and with imponderable fluids and the question of their separateness or unity. These directions were antithetical to Cavendish’s thought. Likewise, chemistry tended to follow Lavoisier’s direction, about which Cavendish had strong reservations. Cavendish was intellectually isolated long before the end of his career. He was not a teacher; he formed or inspired no school. Rather his place in British natural philosophy is as the first after Newton to possess mathematical and experimental talents at all comparable to Newton’s. In intellectual stature Cavendish was without peer in eighteenth-century British natural philosophy.

BIBLIOGRAPHY

I. Original Works. Cavendish’s two electrical papers from the Philosophical Transactions and the bulk of his electrical MSS are published in The Electrical Researches of the Honourable Henry Cavendish, J. Clerk Maxwell, ed. (Cambridge, 1879), also in Cass Library of Science Classics (London, 1967). A rev, ed. of this work is The Scientific Papers of the Honourable Henry Cavendish, F. R. S., 1: The Electrical Researches, J. Clerk Maxwell, ed., rev with notes by Sir Joseph Larmor (Cambridge, 1921). There is also a companion volume containing the rest of Cavendish’s papers from the Philosophical Transactions, together with a selection of his MSS on chemistry, heat, meteorology, optics, mathematics, dynamics, geology, astronomy, and magnetism: The Scientific Researches of the Honourable Henry Cavendish, F. R. S., 2: Chemical and Dynamical, ed. with notes by Sir Edward Thorpe (Cambridge, 1921), with contributions by Charles Chree, Sir Frank Watson Dyson. Sir Archibald Geikie, and Sir Joseph Larmor. Some additional Cavendish MSS relevant to the water controversy are printed in the Rev. W. Vernon Harcourt’s address in the British Association Report (1839), pp. 3–68 plus 60 pp. of lithographed facsimiles. The correspondence between Cavendish and Joseph Priestley is published in A Scientific Autobiography of Joseph Priestley, 1733–1804, ed. with commentary by Robert E. Schofield (Cambridge, Mass., 1966). The vast bulk of Cavendish’s MS papers and correspondence has not been published; it is deposited in Chatsworth, in the possession of the duke of Devonshire.

II.Secondary Literature. On Cavendish or his work, see A. J. Berry, Henry Cavendish: His Life and Scientific Work (London, 1960); J. B. Biot, “Cavendish (Henri),” in Biogmphie universelle, 2nd ed., VII, 272–273; Henry Brougham, “Cavendish,” in Lives of Men of Letters and Science Who Flourished in the Time of George III (Philadelphia, 1845), pp. 250–259; James Gerald Crowther, Scientists of the Industrial Revolution: Joseph Black, James Watt, Joseph Priestley, Henry Cavendish (London, 1962); Georges Cuvier, “Henry Cavendish,” trans. D, S. Faber, in Great Chemists, E. Faber, ed. (New York, 1961), pp. 229–238; Humphry Davy’s estimate of Cavendish, in John Davy, Memoirs of the Life of Sir Humphry Davy, Bart., I (London, 1836), 220–222; Russell McCormmach, “The Electrical Researches of Henry Cavendish,” unpub. diss. (Case Institute of Technology, 1967); “John Michell and Henry Cavendish: Weighing the Stars,” in British Journal for the History of Science, IV (1968), 126–155; “Henry Cavendish: A Study of Rational Empiricism in Eighteenth-Century Natural Philosophy,” in Isis (1970); J. R. Partington, “Cavendish,” in A History of Chemistry, III (London, 1962), 302–362; Robert E. Schofield, Mechanism and Materialism: British Natural Philosophy in an Age of Reason (Princeton, 1970), ch. 10; Thomas Thomson’s estimate of Cavendish, in his History of Chemistry, I (London, 1830), 336–349. George Wilson, The Life of the Honourable Henry Cavendish (London, 1851); and Thomas Young, “Life of Cavendish,” in Scientific Papers of the Honourable Henry Cavendish, I, 435–447.

Russell McCormmach

Henry Cavendish

The English physicist and chemist Henry Cavendish (1731-1810) determined the value of the universal constant of gravitation, made noteworthy electrical studies, and is credited with the discovery of hydrogen and the composition of water.

Henry Cavendish was born on Oct. 10, 1731, the elder son of Lord Charles Cavendish and Lady Anne Grey. He entered Peterhouse, Cambridge, in 1749 and left after 2 years without taking a degree. He never married and was so reserved that there is little record of his having any social life except occasional meetings with scientific friends. His death (Feb. 24, 1810) he faced with the same equanimity with which he faced the unavoidable breaking of apparatus in the course of increasing knowledge. He was buried in All Saints Church, Derby.

Cavendish's work and reputation have to be considered in two parts: the one relating to his published work, the other to the large amount he did not publish. During his lifetime he made notable discoveries in chemistry mainly between 1766 and 1788 and in electricity between 1771 and 1788. In 1798 he published a single notable paper on the density of the earth, but interest in this subject was evidently of long standing.

Contributions to Chemistry

At the time Cavendish began his chemical work, chemists were just beginning to recognize that the "airs" which were evolved in many chemical reactions were distinct entities and not just modifications of ordinary air. Cavendish reported his own work in Three Papers Containing Experiments on Factitious Air in 1766. These papers added greatly to knowledge of the formation of "inflammable air" (hydrogen) by the action of dilute acids on metals. Cavendish also distinguished the formation of oxides of nitrogen from nitric acid. Their true chemical character was not yet known, but Cavendish's description of his observations had almost the same logical pattern as if he were thinking in modern terms, the principal difference being that he used the terminology of the phlogiston theory (that is, a burning substance liberates into its surroundings a principle of inflammability).

Cavendish's other great merit is his experimental care and precision. He measured the density of hydrogen, and although his figure is half what it should be, it is astonishing that he even found the right order of magnitude, considering how difficult it was to manage so intractable a substance. Not that his apparatus was crude; where the techniques of his day allowed, his apparatus (like the splendid balance surviving at the Royal Institution) was capable of refined results.

Cavendish investigated the products of fermentation, showing that the gas from the fermentation of sugar is indistinguishable from the "fixed air" characterized as a constituent of chalk and magnesia by Black (both are, in modern language, carbon dioxide).

Another example of Cavendish's technical expertise was Experiments on Rathbone-Place Water (1767), in which he set the highest possible standard of thoroughness and accuracy. It is a classic of analytical chemistry. In it Cavendish also examined the phenomenon of the retention of "calcareous earth" (chalk, calcium carbonate) in solution, and in doing so he discovered the reversible reaction between calcium carbonate and carbon dioxide to form calcium bicarbonate, the cause of temporary hardness of water. He also found out how to soften such water by adding lime (calcium hydroxide).

In his study of the methods of gas analysis Cavendish made one remarkable observation. He was sparking air with excess oxygen (to form oxides of nitrogen) over alkali until no more absorption took place and noted that a tiny amount of gas could not be further reduced, "so that if there is any part of the phlogisticated air of our atmosphere which differs from the rest, and cannot be reduced to nitrous acid, we may safely conclude, that it is not more than 1/120 part of the whole." As is now known, he had observed the noble gases of the atmosphere.

One of Cavendish's researches on the currently engrossing problem of combustion made an outstanding contribution to fundamental theory. Without seeking particularly to do so, in 1784 Cavendish determined the composition of water, showing that it was a compound of oxygen and hydrogen ("dephlogisticated air" and "inflammable air"). Joseph Priestley had reported an experiment of Warltire in which the explosion of the two gases had left a dew on the sides of a previously dry vessel. Cavendish studied this, prepared water in measurable quantity, and got an approximately correct figure for its volume composition.

Electrical Researches

Cavendish published only a fraction of the experimental evidence he had available to support his theories, but his contemporaries were convinced of the correctness of his conclusions. He was not the first to profound an inverse-square law of electrostatic attraction, but Cavendish's exposition, based in part on mathematical reasoning, was the most effective. He founded the study of the properties of dielectrics and also distinguished clearly between quantity of electricity and what is now called potential.

Cavendish had the ability to make an apparently limited study yield far-reaching results. An example is his study of the origin of the ability of some fish to give an electric shock. He made up imitation fish of leather and wood, soaked in salt water, with pewter attachments representing the organs of the fish which produced the effect. By using Leyden jars to charge the imitation organs, he was able to show that the results were entirely consistent with the fish's being able to produce electricity. This investigation was among the earliest in which the conductivity of aqueous solutions was studied.

Cavendish began to study heat with his father, then returned to the subject in 1773-1776 with a study of the Royal Society's meteorological instruments, in the course of which he worked out the most important corrections to be employed in accurate thermometry. In 1783 he published a study of the means of determining the freezing point of mercury. In it he added a good deal to the general theory of fusion and freezing and the latent heat changes accompanying them.

Cavendish's most elaborate (and celebrated) investigation was that on the density of the earth. He took part in a program to measure the length of a seconds pendulum in the vicinity of a large mountain (Schiehallion). Variations from the period on the plain would show the attraction exerted by the mountain, from which the density of its substance could be calculated. Cavendish also approached the subject in a more fundamental way by determining the force of attraction of a very large, heavy lead ball for a very small, light ball. The ratio between this force and the weight of the light ball would furnish the mass of the earth. His results were unquestioned and unsurpassed for nearly a century.

Unpublished Works

Had Cavendish published all his work, his great influence would undoubtedly have been greater, but in fact he left in manuscript form a vast amount which often anticipated that of his successors. It came to light only bit by bit until the thorough study undertaken by Maxwell (published in 1878) and by Thorpe (published in 1921). In these notes is to be found such material as the detail of his experiments to examine the law of electrostatic force, the conductivity of metals, and many chemical questions such as a theory of chemical equivalents. He had a theory of partial pressures before Dalton.

However, the history of science is full of instances of unpublished works which might have influenced others but in fact did not. Whatever he did not reveal, Cavendish gave his colleagues enough to help them on the road to modern conceptions. Nothing he did has been rejected, and for this reason he is still, in a unique way, part of modern life.

Further Reading

The Scientific Papers of the Hon. Henry Cavendish: Edited from the Published Papers and the Cavendish Manuscripts was published in two volumes: vol. 1, The Electrical Researches, edited by J. Clerk Maxwell (1879), and vol. 2, The Chemical and Dynamical Researches, edited by Sir Edward Thorpe and others (1921). A straightforward account of Cavendish's life and work is A. J. Berry, Henry Cavendish (1960), which includes a useful select bibliography. George Wilson, The Life of the Honble. Henry Cavendish (1851), is available in many libraries. James R. Partington, A History of Chemistry, vol. 3 (1962), contains a very full account of Cavendish's chemical work and some discussion of his electrical work. □

Henry Cavendish

Born: October 10, 1731
Nice, France
Died: February 24, 1810
London, England
English physicist and chemist

The English physicist and chemist Henry Cavendish determined the value of the universal constant of gravitation, made noteworthy electrical studies, and is credited with the discovery of hydrogen and the composition of water.

Early years

Henry Cavendish was born in Nice, France, on October 10, 1731, the oldest son of Lord Charles Cavendish and Lady Anne Grey, who died a few years after Henry was born. As a youth he attended Dr. Newcomb's Academy in Hackney, England. He entered Peterhouse, Cambridge, in 1749, but left after three years without taking a degree.

Cavendish returned to London, England to live with his father. There, Cavendish built himself a laboratory and workshop. When his father died in 1783, Cavendish moved the laboratory to Clapham Common, where he also lived. He never married and was so reserved that there is little record of his having any social life except occasional meetings with scientific friends.

Contributions to chemistry

During his lifetime Cavendish made notable discoveries in chemistry, mainly between 1766 and 1788, and in electricity, between 1771 and 1788. In 1798 he published a single notable paper on the density of the earth. At the time Cavendish began his chemical work, chemists were just beginning to recognize that the "airs" that were evolved in many chemical reactions were clear parts and not just modifications of ordinary air. Cavendish reported his own work in "Three Papers Containing Experiments on Factitious Air" in 1766. These papers added greatly to knowledge of the formation of "inflammable air" (hydrogen) by the action of dilute acids (acids that have been weakened) on metals.

Cavendish's other great achievement in chemistry is his measuring of the density of hydrogen. Although his figure is only half what it should be, it is astonishing that he even found the right order. Not that his equipment was crude; where the techniques of his day allowed, his equipment was capable of precise results. Cavendish also investigated the products of fermentation, a chemical reaction that splits complex organic compounds into simple substances. He showed that the gas from the fermentation of sugar is nearly the same as the "fixed air" characterized by the compound of chalk and magnesia (both are, in modern language, carbon dioxide).

Another example of Cavendish's ability was "Experiments on Rathbone-Place Water"(1767), in which he set the highest possible standard of accuracy. "Experiments" is regarded as a classic of analytical chemistry (the branch of chemistry that deals with separating substances into the different chemicals they are made from). In it Cavendish also examined the phenomenon (a fact that can be observed) of the retention of "calcareous earth" (chalk, calcium carbonate) in solution (a mixture dissolved in water). In doing so, he discovered the reversible reaction between calcium carbonate and carbon dioxide to form calcium bicarbonate, the cause of temporary hardness of water. He also found out how to soften such water by adding lime (calcium hydroxide).

One of Cavendish's researches on the current problem of combustion (the process of burning) made an outstanding contribution to general theory. In 1784 Cavendish determined the composition (make up) of water, showing that it was a combination of oxygen and hydrogen. Joseph Priestley (1733–1804) had reported an experiment in which the explosion of the two gases had left moisture on the sides of a previously dry container. Cavendish studied this, prepared water in measurable amount, and got an approximate figure for its volume composition.

Electrical research

Cavendish published only a fraction of the experimental evidence he had available to support his theories, but his peers were convinced of the correctness of his conclusions. He was not the first to discuss an inverse-square law of electrostatic attraction (the attraction between opposite—positive and negative—electrical charges). Cavendish's idea, however, based in part on mathematical reasoning, was the most effective. He founded the study of the properties of dielectrics (nonconducting electricity) and also distinguished clearly between the amount of electricity and what is now called potential.

Cavendish had the ability to make a seemingly limited study give far-reaching results. An example is his study of the origin of the ability of some fish to give an electric shock. He made up imitation fish of leather and wood soaked in salt water, with pewter (tin) attachments representing the organs of the fish that produced the effect. By using Leyden jars (glass jars insulated with tinfoil) to charge the imitation organs, he was able to show that the results were entirely consistent with the fish's ability to produce electricity. This investigation was among the earliest in which the conductivity of aqueous (in water) solutions was studied.

Cavendish began to study heat with his father, then returned to the subject in 1773–1776 with a study of the Royal Society's meteorological instruments. (The Royal Society is the world's oldest and most distinguished scientific organization.) During these studies he worked out the most important corrections to be employed in accurate thermometry (the measuring of temperature). In 1783 he published a study of the means of determining the freezing point of mercury. In it he added a good deal to the general theory of fusion (melting together by heat) and freezing and the latent heat changes that accompany them (the amount of heat absorbed by the fused material).

Cavendish's most celebrated investigation was that on the density of the earth. He took part in a program to measure the length of a seconds pendulum close to a large mountain (Schiehallion). Variations from the period on the plain would show the attraction put out by the mountain, from which the density of its substance could be figured out. Cavendish also approached the subject in a more fundamental way by determining the force of attraction of a very large, heavy lead ball for a very small, light ball. The ratio between this force and the weight of the light ball would result in the density of the earth. His results went unquestioned for nearly a century.

Unpublished works

Had Cavendish published all of his work, his already great influence would undoubtedly have been greater. In fact, he left in manuscript form a vast amount of work that often anticipated the work of those who followed him. It came to light only bit by bit until the thorough study undertaken by James Maxwell (1831–1879) and by Edward Thorpe (1845–1925). In these notes is to be found such material as the detail of his experiments to examine the conductivity of metals, as well as many chemical questions such as a theory of chemical equivalents. He even had a theory of partial pressures before John Dalton (1766–1844).

However, the history of science is full of instances of unpublished works that might have influenced others but in fact did not. Whatever he did not reveal, Cavendish gave other scientists enough to help them on the road to modern ideas. Nothing he did has been rejected, and for this reason he is still, in a unique way, part of modern life.

For More Information

Berry, A. J. Henry Cavendish. London: Hutchinson, 1960.

Jungnickel, Christa. Cavendish: The Experimental Life. Lewisburg, PA: Bucknell University Press, 1999.

Cavendish, Henry

ENGLISH PHYSICIST AND CHEMIST
1731–1810

Henry Cavendish, born in Nice, France to an aristocratic English family, was an avid and excellent experimenter. At the age of forty, he inherited an immense fortune that afforded him the luxury of pursuing his scientific interests (he was described by some as the "richest of all the learned and the most learned of all the rich"). He was an extraordinarily odd man, whose extreme shyness rendered him a virtual recluse. Despite this, he is remembered as a great, albeit humble, man who devoted his life to science.

Cavendish explored all areas of science, including astronomy, optics, electricity, geology, and pure mathematics. Among his accomplishments are the first calculation of Earth's mass (his results were just 10% off modern measurements) and the introduction of the concept of voltage . His principal interest nevertheless was experimental chemistry. His most famous contribution to science was the discovery and description of the properties of hydrogen and its status as a constituent element in water.

Cavendish, like many before him, noticed that a gas was produced when zinc or iron was dropped into an acid. He called this gas "inflammable air" (known today as hydrogen). Using his exacting experimental skills, Cavendish was the first to distinguish this inflammable air from ordinary air and to investigate its specific properties. He presented a paper detailing his findings in 1766.

The importance of inflammable air became clear about fifteen years after Cavendish presented his paper. Joseph Priestley (1733–1804) was also interested in gases, and in 1781 told Cavendish of the results of some of his own experiments. When Priestley used an electrostatic machine to spark ordinary air with inflammable air, he noticed that water was formed. Cavendish repeated this experiment, as well as others like it, but using oxygen (or, as he called it, "dephlogisticated air") in place of ordinary air.

Cavendish's results were the same as Priestley's, but he did not publish or present his findings. Sometime before 1783, however, Cavendish did advise Priestley of his results. Priestley told Charles Blagden, secretary of the Royal Society in London, and Blagden in turn informed Antoine Lavoisier (1743–1794) in France.

Cavendish did eventually publish his findings on the formation of water in 1784. But Lavoisier claimed that he had discovered how water was formed—in fact, it was Lavoisier who coined the name "hydrogen," which means "water former." It was not until the mid-nineteenth century, when Cavendish's notebooks were published, that he was given sole credit for discovering that water is composed of inflammable air and dephlogisticated air, or hydrogen and oxygen.

As may be seen in his collaborative work with Priestley in the investigation of the composition of water, Cavendish did not allow his natural shyness to impede his work. The relationship between him and Priestley demonstrates not only Cavendish's devotion to science, but the general cooperative nature of scientific investigation. By sharing the results of their separate experiments, these two great scientists were able to discover the composition of water.

For all of his scientific genius, Cavendish was a pronounced eccentric. He rarely left his house except for weekly meetings of the Royal Society, and even there, despite being one of the most famous scientists of his time, he was known to linger outside the meeting room and enter only when he thought no one would notice. He could barely tolerate the company of women; if any of his female servants happened to cross his path, she was likely to be fired. Though enormously wealthy, he was reputed to own but one suit, and an old-fashioned one at that.

Cavendish lived a lonely and humble life, committed to the cultivation of science. To him, science was measurement, and he showed himself to be one of the most respected experimentalists of the time. His death was as lonely as his life; when he sensed that the end was near, he instructed his servant to leave the room and not come back until a certain time. When the servant returned, he found that Cavendish had died.

see also Hydrogen; Lavoisier, Antoine; Priestley, Joseph.

Lydia S. Scratch

Bibliography

Berry, Arthur John (1960). Henry Cavendish: His Life and Scientific Work. London: Hutchinson.

Jaffe, Bernard (1976). Crucibles: The Story of Chemistry from Ancient Alchemy to Nuclear Fission. New York: Dover.

Jungnickel, Christa, and McCormmach, Russel (1999). Cavendish: The Experimental Life. Cranbury, NJ: Bucknell.

Internet Resources

"Henry Cavendish." BBC History. Available from <http://www.bbc.co.uk>.

Henry Cavendish

1731-1810

English Chemist and Physicist

Henry Cavendish made many significant contributions to a wide range of scientific endeavors and is regarded as one of the greatest scientist of his day. He is best known for his work with the chemistry of gases, the discovery of hydrogen, the determination of the composition of water, the synthesis of water, and his contributions to electrical theory.

Henry Cavendish was born into one of England's most prominent families; two of his grandfathers were dukes. When he received his inheritance, he became one of the wealthiest people of his time. He was educated at exclusive Hackney School and attended Peterhouse College at Cambridge University. He never received a degree, refusing to declare his acceptance of the Church of England, a requirement of all graduates. Instead he returned home to assist his father in the laboratory that the elder Cavendish, a well-known amateur scientist, maintained in their home. He subsequently followed in his father's footsteps, working for the rest of his life in his own private laboratory in his home.

Cavendish was an extremely shy and eccentric person, an introvert and recluse who seldom left his house. It is not surprising that he also was reluctant to publish the results of his scientific work, most of which remained unpublished until the Scottish physicist James Clerk Maxwell (1831-1879) edited and published it after Cavendish's death.

He was among the first scientists to use quantitative methods in chemistry. He performed extensive experiments with gases, especially hydrogen ("inflammable air") and carbon dioxide ("fixed air"). He determined that hydrogen is a separate substance and that water is not an element but is made up of hydrogen and oxygen. He succeeded in synthesizing water from its constituent elements. He also discovered nitric acid.

Cavendish made significant groundbreaking contributions to the study of electricity. He suggested that an electric atmosphere surrounds a charged substance, providing the basis for the development of electric field theory. He proposed the concept of electrical potential and discovered that the potential across a conductor is proportional to the current through it. He was one of several scientists who independently worked out the inverse square law of electrical attraction and repulsion: the attraction between opposite charges or the repulsion between two charges having the same sign is inversely proportional to the distance between the charges. He was first to determine and study the electrical conductivity of salt solutions. It is interesting to note that Cavendish had no instrument to measure electric current. Instead, he used the reaction of his own body to the electrical shock to measure the intensity of the current, developing a quantitative scale based on the intensity of his reaction to the shock.

As a part of a research effort he undertook late in life, he invented an extremely sensitive torsion balance and used it to determine the constant in Isaac Newton's (1642-1727) universal law of gravitation. He was also able to measure the density of Earth using data obtained with this balance.

Cavendish also performed extensive experiments with heat. His work with the calibration of thermometers, the measurement of vapor pressures, latent heats, and specific heats is particularly noteworthy. He rejected the theory that heat is a substance that flows from one object to another. Instead he championed the explanation of heat as the motion of particles within substances.

Cavendish died at age 78, a recluse with neither close friends nor any direct descendants to inherit his vast wealth. The various relatives who became his heirs honored him by endowing the Cavendish Laboratory at Cambridge University. This laboratory quickly became a major center for developments in experimental and theoretical physics and remains so today.

J. WILLIAM MONCRIEF