G. Johnstone Stoney.html

George Johnstone Stoney (15 February 1826, Oak Park, near Birr, County Offaly, Ireland – 5 July 1911, London, England) was an Irish physicist who was the first to propose, in 1874, that there was a "fundamental unit quantity of electricity."¹ In 1891, he proposed to call this unit quantity the electron.²³ He was also the first to propose a system of natural units for physical quantities.⁴

1 Life
2 Scientific Work
- 2.1 The Stoney Scale
3 Honours
4 See also
5 Footnotes
6 References
7 External links

Life

Stoney was born in the Irish midlands, into an old-established Anglo-Irish family who had lost their land at the time of the Great Famine.⁵ He attended Trinity College, Dublin, graduating with a B.A. in 1848 and an M.A. in 1852. In 1848 he became the first regular Astronomical Assistant to William Parsons, 3rd Earl of Rosse at Birr Castle, County Offaly, where Parsons had built what was then the world's largest telescope, the 72-inch Leviathan of Parsonstown.

In 1852, Stoney became Professor of Natural Philosophy at Queen's College Galway (now the National University of Ireland, Galway). In 1857, he moved to Dublin as Secretary of the Queen's University of Ireland, based in Dublin Castle. While in Dublin, he was honorary secretary to the Royal Dublin Society for over 20 years, and then served as a vice-president. He was able to continue his scientific and academic work in close association with this society. He subsequently became superintendent of the Civil Service Examinations in Ireland, a post he held until his 1893 retirement.¹

Stoney was the uncle of the noted mathematical physicist George FitzGerald. The two were in regular communication on scientific matters, and Fitzgerald went on to become a profesor of "natural and experimental philosophy" (i.e., physics) in Trinity College, Dublin. Stoney was also distantly related to Alan Turing.⁵

Stoney married his cousin, and they had 2 sons and 3 daughters. The family resided on a street in Dundrum, Dublin, now named Stoney Road in his honour. Upon his 1893 retirement, family reasons led him to move to Notting Hill, London, where he spent the remainder of his life. His cremated ashes were buried in Dundrum.

Scientific Work

Stoney published 75 scientific papers in his lifetime, making significant contributions to cosmology and to the kinetic theory of gases. In 1868, he estimated the number of molecules in a cubic millimetre of gas, at standard temperature and pressure, to be 10¹⁸.⁶

Reasoning from data on how much current was required to deposit a given mass of metal in electrolytic experiments, Stoney was the first to propose that there is an "atom of electricity," and to predict its charge, now called the elementary charge. (Helmholtz independently came near this discovery in 1881.) Hence he was the first to propose that electric charge is quantized. He at first called this fundamental unit of electric charge the "electrene," then in 1891 renamed it the electron, the name it has to this day. His theoretical work lit the way towards the discovery of the electron by J.J. Thomson in 1897.

The Stoney Scale

Stoney was the first to see that if certain fundamental physical constants are assigned the value 1, an entire system of measurement units, now called Stoney units, for all physical quantities (building on units of mass, length, time, and electric charge) can be derived, with mass being the cornerstone. Hence he was the first to construct a system of natural units.

Contemporary physics has settled on the Planck scale as the most suitable scale for a unified theory. Stoney anticipated as follows a fair part of the reasoning that led to the Planck scale.⁷ Like Planck after him, Stoney realized that large-scale effects such as gravity, and small-scale effects such as electromagnetism, naturally imply an intermediate scale where physical differences might be rationalized. For an elementary introduction to Stoney units and their relation to Planck units, see Barrow (2002: ).

Expressed in contemporary terminology, the Stoney mass $m_S \$ is:

$m_S=\sqrt{\frac{e^2}{4 \pi \epsilon_0 G}} = \sqrt{\alpha} m_P$

where:

ε₀ is the permittivity of free space;
e is the elementary charge (the charge carried by the electron, whose existence Stoney was the first to hypothesize);
G is the gravitational constant;
α is the fine-structure constant, (unknown in Stoney's day), and
m_P is the Planck mass.

Like the Planck scale, the Stoney scale functions as a symmetrical link between microcosmic and macrocosmic processes in general, even though the Stoney scale appears uniquely oriented towards the unification of electromagnetism and gravity. For example, whereas the Planck length $\ l_P$ is the mean square root of the reduced Compton wavelength and half the gravitational radius of any mass, the Stoney length $\ l_S$ is the mean square root of the electromagnetic radius and half the gravitational radius of any mass m. Thus:

$l_P=\sqrt{\frac{\hbar}{m c}.\frac{G m}{c^2}}$ and

$l_S=\sqrt{\frac{e^2}{4 \pi \epsilon_0 m c^2}.\frac{G m}{c^2}},$

where $\hbar \$ is the reduced Planck's constant and c is the speed of light.

There are two reasons why Stoney units are no more than mathematical constructs. One is that even now, G is known to no more than about 1 part in 7000. The other is that the state of technology places a practical lower limit to how small a length can be measured. If the Stoney length is the minimum length, then either a body's electromagnetic radius or its half gravitational radius is a physical impossibility, since one of these must be smaller than the Stoney length. If the Planck length is the minimum length, then either a body's reduced Compton wavelength or its half gravitational radius is a physical impossibility, since one of these must be smaller than the Planck length. Hence neither the Stoney length nor the Planck length can be "the" minimum length.

Present-day convention has it that the Planck scale is the scale of vacuum energy; at smaller scales, space and time do not have physical significance. This convention has relegated the Stoney scale to being merely of historical interest. Before the Planck scale became dominant, Hermann Weyl attempted to construct a unified theory by associating a gravitational unit of charge with the Stoney length. While Weyl's theory led to significant mathematical innovations, it is generally believed to lack physical significance.⁸⁹

Honours

Stoney was a member of the Royal Society for almost fifty years. He was a foreign member of the America Academy of Science, and of the Philosophical Society of America.¹ In 1899, he was the first recipient of the Boyle Medal, inaugurated by the Royal Dublin Society to recognise scientific research of exceptional merit by Irishmen. Craters on Mars and the Moon are named after him.

Footnotes

^ ^a ^b ^c The Daily Express (6 July 1911). "George Johnstone Stoney 1826-1911". Retrieved on 2008-10-22.
^ Stoney Uses the Term Electron
^ Jammer, Max (1956). Concepts of Force - A Study of the Foundations of Dynamics. New York: Dover Publications, Inc.. ISBN 0-486-40689-X.
^ Stoney, G.J., 1881, "On the Physical Units of Nature." Phil. Mag. 11: 384.
^ ^a ^b McCartney, Mark; Andrew Whitaker (2003). Physicists of Ireland: Passion and Precision. CRC Press. pp. 126. ISBN 9780750308663.
^ Stoney, G.J., 1868, " ," Phil. Mag. 36: 141.
^ Stoney G., 1881, "On The Physical Units of Nature," Phil. Mag. 11: 381-91.
^ O'Raifeartaigh L., 1997. The Dawning of Gauge Theory. Princeton Univ. Press.
^ Gorelik G., 2002, "Herman Weyl and Large Numbers in Relativistic Cosmology," Einstein Studies in Russia, Balashov, Y., and Vizgin, V., eds. Boston: Birkhaeuser.

References

John D. Barrow, 2002. The Constants of Nature: The Numbers that Encode the Deepest Secrets of the Universe Pantheon Books.
Keller, Alex, 1983. The Infancy of Atomic Physics. Hercules in His Cradle. Oxford University Press. ISBN 0-19-853904-5

External links

Stoney, G. J., 1894, "Of the 'Electron,' or Atom of Electricity," Philosophical Magazine 38 (Series 5): 418-20.

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