Henry Cavendish: Wikis

  
  

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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

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

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/kg2 [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

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

See also

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. doi:10.1098/rstl.1798.0022. 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

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

Quotes

Up to date as of January 14, 2010

From Wikiquote

Henry Cavendish, FRS (10 October 173124 February 1810) was a British scientist noted for his discovery of hydrogen or what he called "inflammable air". Cavendish is also known for the Cavendish experiment, his measurement of the Earth's density, and early research into electricity.

Sourced

  • Young people must break machines to learn how to use them; get another made!
    • when he was told that one of his valuable instruments was broken by a young man, as quoted in Biographical Memoir of Henry Cavendish, by Georges Cuvier, The Edinburgh New Philosophical Journal (1828), p. 222.

External links

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Simple English

File:Henry
Henry Cavendish

Henry Cavendish (October 10, 1731 - February 24, 1810) was a British scientist. He is famous for discovering hydrogen.[1]

He measured the Earth's mass and density with Cavendish Experiment. He studied at Peterhouse, which is part of the University of Cambridge but he could not graduate from there.

He built a laboratory near London, where he worked for nearly fifty years, but he only published about 20 scientific papers. Even so, he is called one of the greatest scientists of his period.

Cavendish claimed that the force between the two electrical objects gets smaller as they get further apart. If the distance between them doubled, the force would be one quarter what it was before. This was based on the inverse-square law. He explained the concept of electric potential, which was already known in Math but had been never used in electrical experiments until that day. He developed the thought of all points on a good conductor's surface have the same potential energy beside a common reference point. Because of no possibility to measure electric current, he used his body as a machine which measures strength of electric current. All Cavendish's explorations in his notebook was found and confirmed by James Clerk Maxwell.

References

  1. Gay, Peter; Time-Life Books (1966). "The Practical Philosophers". Age of Enlightenment. Time. pp. 27. 







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