Henry Cavendish

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Henry Cavendish

Library of Congress

[b. Nice, France, October 10, 1731, d. London, February 24, 1810]

A wealthy recluse, Cavendish worked on scientific problems for his entire long life. He was the first to show that water is a compound and that air is a mixture -- previously both were thought to be elements. In the process he discovered hydrogen and developed methods for weighing and measuring gases. But he is best known for his experiment determining the gravitational constant G. This experiment is often called "weighing the Earth," since knowing G permits one to calculate Earth's mass. Cavendish used Earth's mass to find its density, which is greater than that of stone, implying a heavy core. He also made advances in the study of heat and electricity; but these results were not published until long after his death and after their independent discovery by others.

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.

Cavendish, Henry (1731-1810). A nephew of the 3rd duke of Devonshire, he studied in Cambridge and in Paris, before living as a recluse in London. He worked in the new field of pneumatic chemistry, isolating ‘inflammable air’ (hydrogen) and proving that water was not an element but a compound. The Cavendish Laboratory in Cambridge was founded in his memory.

For other persons named Henry Cavendish, see Henry Cavendish (disambiguation).

Henry Cavendish
Henry Cavendish
Born	10 October 1731(1731-10-10) Nice, France
Died	24 February 1810 (aged 78)
Nationality	United Kingdom
Fields	Chemistry, physics
Alma mater	University of Cambridge
Known for	Discovery of hydrogen Measured the Earth's density

Henry Cavendish FRS (10 October 1731 – 24 February 1810) was a British scientist noted for his discovery of hydrogen or what he called "inflammable air".^[1] He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and gave the element its name. Cavendish is also known for the Cavendish experiment, his measurement of the Earth's density, and early research into electricity.

Contents 1 Personal life 2 Gases and the atmosphere 3 Density of the Earth 4 Electrical researches 5 Selected writings 6 See also 7 Notes and references 8 Further reading 9 External links

Personal life

Henry Cavendish was born on 10 October 1731 in Nice, France, where his family was living at the time. His mother was Lady Anne Grey, daughter of the Duke of Kent and his father was Lord Charles Cavendish, son of 2nd Duke of Devonshire. The family traces its lineage across eight centuries to Norman times and was closely connected to many aristocratic families of Great Britain.

At age 11, Cavendish was a pupil at Peter Newcome's School in Hackney. At age 18 (on 24 November 1749) he entered the University of Cambridge in St Peter's College, now known as Peterhouse, but left four years later on 23 February 1753 without graduating.^[2][3] His first paper, "Factitious Airs", appeared thirteen years later, in 1766.

Cavendish was silent, and solitary, viewed as somewhat eccentric,he only spoke to his female servants by notes and formed no close personal relationships outside his family. By one account, Cavendish had a back staircase added to his house in order to avoid encountering his housekeeper because he was especially shy of women. The contemporary accounts of his personality have led some modern commentators, such as Oliver Sacks, to speculate that he had Asperger syndrome, though he may merely have been painfully shy. His only social outlet was the Royal Society Club, whose members dined together before weekly meetings. Cavendish seldom missed these meetings, and was profoundly respected by his contemporaries. However his shyness made those who "sought his views... speak as if into vacancy. If their remarks were...worthy, they might receive a mumbled reply."^[4] He also enjoyed collecting fine furniture exemplified by his purchase of a set of "ten inlaid satinwood chairs with matching cabriole legged sofa" documented to have been acquired by Cavendish himself.^[5]

Because of his asocial and secretive behaviour, Cavendish often avoided publishing his work, and much of his findings were not even told to his fellow scientists. In the late nineteenth century, long after his death, James Clerk Maxwell looked through Cavendish's papers and found things for which others had been given credit. Examples of what was included in Cavendish's discoveries or anticipations were Richter's Law of Reciprocal Proportions, Ohm's Law, Dalton's Law of Partial Pressures, principles of electrical conductivity (including Coulomb's Law), and Charles's Law of Gases.

Cavendish died in 1810 and was buried, along with many of his ancestors, in the church that is now Derby Cathedral (and the road he used to live on in Derby has been named after him. The University of Cambridge's Cavendish Laboratory was endowed by one of Cavendish's later relatives, William Cavendish, 7th Duke of Devonshire (Chancellor of the University from 1861 to 1891).

Gases and the atmosphere

Cavendish's apparatus for making and collecting hydrogen^[1]

Cavendish is considered to be one of the so-called pneumatic chemists of the eighteenth and nineteenth centuries, along with, for example, Joseph Priestley, Joseph Black, and Daniel Rutherford. By combining metals with strong acids, Cavendish made hydrogen (H₂) gas, which he isolated and studied. Although others, such as Robert Boyle, had prepared hydrogen gas earlier, Cavendish is usually given the credit for recognizing its elemental nature.

Cavendish observed that hydrogen, which he called "inflammable air", reacts with oxygen, then known as "dephlogisticated air", to form water. James Watt and Antoine Lavoisier made a similar observation, resulting in a controversy as to who should receive credit for it.

Cavendish also accurately determined the composition of Earth's atmosphere. In a 1785 paper, he described experiments in which hydrogen and ordinary air were combined in known ratios, and then exploded with a spark of electricity. In each case, Cavendish observed both the formation of water and that the gas volume after the explosion was always less than it was before it. By careful measurements he was led to conclude that, "common air consists of one part of dephlogisticated air [oxygen], mixed with four of phlogisticated [nitrogen]".^[6][7]

The same paper described an experiment in which Cavendish was able to remove, in modern terminology, both the oxygen and nitrogen gases from a sample of atmospheric air until only a small bubble of unreacted gas was left in the original sample. From this experiment Cavendish concluded that not more than 1/120 of the Earth's atmosphere was other than oxygen and nitrogen.^[8] Although a seemingly small fraction, about 100 years later William Ramsay and Lord Rayleigh showed that this residual gas contained argon, an element that was unknown at the time.

Density of the Earth

Main article: Cavendish experiment

In addition to his achievements in chemistry, Cavendish is also known for the Cavendish experiment, the first to measure the force of gravity between masses in a laboratory and to produce an accurate value for Earth's density. His work led others to accurate values for the gravitational constant (G) and Earth's mass. Based on his results, one can calculate a value for G of 6.754 × 10⁻¹¹N-m²/kg^{2 [9]}, which compares favourably with the modern value of 6.67428 × 10⁻¹¹N-m²/kg².^[10]

The equipment Cavendish used was designed and built by geologist John Michell, who died before he could begin the experiment. The apparatus was sent in crates to Cavendish, who completed the experiment in 1797 – 1798,^[4] and published the results.^[11] Cavendish noticed that Michell's apparatus would be sensitive to temperature differences and induced air currents so he made modifications by isolating the apparatus in a separate room with external controls and telescopes for making observations.^[12]

The experimental apparatus consisted of a torsion balance to measure the gravitational attraction between two 350-pound lead spheres and a pair of 2-inch 1.61-pound lead spheres.^[4] Using this equipment, Cavendish found that the Earth's average density is 5.48 times greater than that of water. John Henry Poynting later noted that the data should have led to a value of 5.448^[13], and indeed that is the average value of the twenty-nine determinations Cavendish included in his paper.^[14]

It is not unusual to find books that erroneously describe Cavendish's work as a measurement either of the gravitational constant (G) or the Earth's mass^[15][16], and this mistake has been pointed out by several authors.^[17][18] In reality, Cavendish's stated goal was to measure the Earth's density, and his result was later used to calculate G. The first time that this constant was used was in 1873, almost 100 years after the Cavendish experiment.^[19] Cavendish's results also can be used to calculate the Earth’s mass.

Cavendish performed his experiment in an outbuilding in the garden of his Clapham Commons estate. For years afterward, his neighbours would point out the building and tell their children that it was where the world was weighed.^[5]

Electrical researches

Henry Cavendish.

Cavendish wrote papers on electrical topics for the Royal Society^[20][21] but the bulk of his electrical experiments did not become known until they were collected and published by James Clerk Maxwell a century later, in 1879, long after other scientists had been credited with the same results. Among Cavendish's discoveries were the following:^[22]

• The concept of electric potential, which he called the "degree of electrification"
• An early unit of capacitance, that of a sphere one inch in diameter
• The formula for the capacitance of a plate capacitor
• The concept of the dielectric constant of a material
• The relationship between electric potential and current, now called Ohm's Law. (1781)
• Laws for the division of current in parallel circuits, now attributed to Charles Wheatstone
• Inverse square law of variation of electric force with distance, now called Coulomb's Law

Selected writings

• Cavendish, Henry (1921). Scientific Papers. 1. Cambridge: Cambridge University Press. http://www.archive.org/details/scientificpapers01caveuoft.  - edited by James Clerk Maxwell and revised by Joseph Larmor
• Cavendish, Henry (1921). Scientific Papers. 2. Cambridge: Cambridge University Press. http://www.archive.org/details/scientificpaper00cavegoog.  - edited by James Clerk Maxwell and revised by Joseph Larmor
• Cavendish, Henry (1879). The Electrical Researches of the Honourable Henry Cavendish. Cambridge: Cambridge University Press. http://books.google.com/books?id=3gYJAAAAIAAJ&pg=PR24&dq=cavendish+henry#PPR3,M1.  - edited by James Clerk Maxwell

See also

• Timeline of hydrogen technologies

Notes and references

1. ^ ^{a b} Cavendish, Henry (1766). "Three Papers Containing Experiments on Factitious Air, by the Hon. Henry Cavendish". Philosophical Transactions 56: 141 – 184. doi:10.1098/rstl.1766.0019. http://books.google.com/books?id=ygqYnSR3oe0C&printsec=frontcover&dq=the+scientific+papers+cavendish#PPA77,M1. Retrieved 6 November 2007. 
2. ^ Henry Cavendish in Venn, J. & J. A., Alumni Cantabrigienses, Cambridge University Press, 10 vols, 1922–1958.
3. ^ Wilson, George (1851). "1". The life of the Hon. Henry Cavendish. Cavendish Society. pp. 17. 
4. ^ ^{a b c} Bryson, B. (2003), "The Size of the Earth": A Short History of Nearly Everything, 59 – 62.
5. ^ ^{a b} McCormmach, R and Jungnickel, C (1996), Cavendish, American Philosophical Society, Philadelphia, ISBN 0871692201, p. 242, 337.
6. ^ See page 376 of Cavendish, Henry (1784). "Experiments on Air". Philosophical Transactions of the Royal Society of London 74: 119 – 153.  The same passage is on page 44 of the Alembic Club reprint of the article.
7. ^ See also pages 261 - 262 of Cavendish by Jungnickel and McCormmach (1996)
8. ^ See page 382 of Cavendish, Henry (1784). "Experiments on Air". Philosophical Transactions of the Royal Society of London 74: 119 – 153.  The same passage is on page 50 of the Alembic Club reprint of the article.
9. ^ Brush, Stephen G.; Holton, Gerald James (2001). Physics, the human adventure: from Copernicus to Einstein and beyond. New Brunswick, N.J: Rutgers University Press. pp. 137. ISBN 0-8135-2908-5. 
10. ^ CODATA Value: Newtonian constant of gravitation
11. ^ Cavendish, Henry (1798). "Experiments to Determine the Density of Earth". Philosophical Transactions of the Royal Society of London 88: 469–526. http://www.jstor.org/stable/106988. 
12. ^ Magie, William Francis. A Source Book in Physics. Cambridge, Mass: Harvard University Press. p. 107. 
13. ^ Poynting, J. H. (1894), "The Mean Density of the Earth" London: Charles Griffin and Company, page 45.
14. ^ Cavendish, Henry, "Experiments to Determine the Density of the Earth", reprinted in A Source Book in Geology, K. F. Mather and S. L. Mason, editors, New York: McGraw-Hill (1939), pages 103 – 107.
15. ^ Tipler, P. A. and Mosca, G. (2003), Physics for Scientists and Engineers: Extended Version, W. H. Freeman ISBN 0-7167-4389-2.
16. ^ Feynman, R. P. (1970), Feynman Lectures On Physics, Addison Wesley Longman , ISBN 0-201-02115-3
17. ^ Clotfelter, B. E. (1987), The Cavendish Experiment as Cavendish Knew It, American Journal of Physics 55 (3), 210-213.
18. ^ Falconer, I. (1999), Henry Cavendish: the man and the measurement , Measurement, Science & Technology 10 (6): 470-477.
19. ^ Cornu, A. and Baille, J. B. (1873), Mutual determination of the constant of attraction and the mean density of the earth, C. R. Acad. Sci., Paris Vol. 76, 954-958.
20. ^ Cavendish, Henry (1771). "An Attempt to Explain Some of the Principal Phaenomena of Electricity, by means of an Elastic Fluid". Philosophical Transactions 61: 564 – 677. doi:10.1098/rstl.1771.0056. 
21. ^ Cavendish, Henry (1776). "An Account of Some Attempts to Imitate the Effects of the Torpedo by Electricity.". Philosophical Transactions 66: 195 – 225. doi:10.1098/rstl.1776.0013. 
22. ^ "Electricity". Encyclopedia Britannica. 1911. http://www.1911encyclopedia.org/Electricity#Cavendish.27s_Researches. 

Further reading

• Dictionary of National Biography, Vol. 3, p. 1261.
• Cavendish: The Experimental Life, C. Jungnickel and R. McCormmach, Bucknell University Press, 1999.

External links

Wikiquote has a collection of quotations related to: Henry Cavendish

• The Life of the Honourable Henry Cavendish by George Wilson, London, 1851.
• Experiments on Air by Henry Cavendish, Edinburgh: William F. Clay (1893) - Alembic Club reprint number 3.
• "The Mean Density of the Earth" by J. H. Poynting, London: Charles Griffin and Company (1894).
• The Laws of Gravitation: Memoirs by Newton, Bouguer and Cavendish, edited and translated by A. Stanley MacKenzie, New York: American Book Company (1900).
• A History of Chemistry by F. J. Moore, New York: McGraw-Hill (1918) - See especially pages 34 – 36.
• Henry Cavendish, English Scientist (1731-1810) from the Encyclopaedia Britannica, 10th Edition (1902).
•  "Cavendish, Henry". Encyclopædia Britannica (11th ed.). 1911. 
• "Cavendish" by Christa Jungnickel and Russell McCormmach, 1996, 414 pages

Awards and achievements
Preceded by John Canton	Copley Medal 1766 jointly with William Brownrigg and Edward Delaval	Succeeded by John Ellis

Authority control: PND: 118668889 | LCCN: n 86866622

Persondata
NAME	Cavendish, Henry
ALTERNATIVE NAMES
SHORT DESCRIPTION	Scientist
DATE OF BIRTH	10 October 1731
PLACE OF BIRTH	Nice, France
DATE OF DEATH	24 February 1810
PLACE OF DEATH

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