The World of Physics

Irving Langmuir

When blood is cleared of its various corpuscles there remains a clear liquid, which was named “plasma” by the great Czech medical scientist, Johannes Purkinje (1787-1869). The use of the term “plasma” for an ionized gas started in 1927 with Irving Langmuir (1881-1957), an American whose achievements ranged from the chemistry of surfaces to cloud seeding for promoting rain, and who in 1932 won the Nobel prize for chemistry. Langmuir worked for the General Electric Co., studying electronic devices based on ionized gases, and the way the electrified fluid carried high velocity electrons, ions and impurities reminded him of the way blood plasma carried red and white corpuscles and germs.

Irving Langmuir’s is credited with two important inventions: the high-vacuum electron tube and the gas-filled incandescent lamp.

Langmuir was born in Brooklyn, New York, and educated in New York and Paris, France. He earned a B.S. from the Columbia University School of Mines and a Ph.D. in chemistry from the University of Gottingen in Germany, where he studied under Nobel laureate Walther Nernst.

His first professional position was as an instructor of chemistry at Stevens Institute in Hoboken, New Jersey, from 1906 to 1909. From there he moved to the General Electric Research Laboratory in Schenectady, New York. What began as a summer job blossomed into a career with the company that lasted the rest of his life. While at G.E., Langmuir received 63 patents and was awarded the 1932 Nobel Prize for Chemistry, as well as numerous other honors. His initial research at General Electric involved low-pressure chemical reactions and the study of the emission of electrons by hot filaments in a vacuum. This work led directly to the invention of the high-vacuum electron tube in 1912 and the gas-filled incandescent lamp in 1913.

Langmuir was responsible for many basic scientific discoveries which played a fundamental role in the development of commercial electrical products as well as in military and general scientific areas. His contributions to atomic theory and the understanding of atomic structure threw light upon the meaning of isotopes. His experiments with oil films on water resulted in the development of two-dimensional or surface chemistry.

In World War II, Langmuir was one of the key advisers in the national defense and wartime scientific research programs, contributing to the development of radar for use by the British and United States armed forces. Langmuir’s studies embraced chemistry, physics, and engineering and were largely the outgrowth of studies of vacuum phenomena. In seeking the atomic and molecular mechanisms of these he investigated the properties of adsorbed films and the nature of electric discharges in high vacuum and in certain gases at low pressures.

Langmuir probe theory is still in wide spread use today for measuring plasma temperatures. He showed that the volt-ampere characteristic of a Langmuir Probe’s can be used to determine a number of plasma parameters, such as, electron and ion temperature, plasma potential, electron and ion density etc, can be easily determined. His work on filaments in gases led directly to the invention of the gas-filled incandescent lamp and to the discovery of atomic hydrogen. He later used the latter in the development of the atomic hydrogen welding process.

Jean Baptiste Joseph Fourier(1766 -1844)

“The profound study of nature is the most fertile source of mathematical discoveries. Not only does this study, offering a definite goal to research, have the advantage of excluding vague questions and fruitless calculations; it is also a sure means of creating Analysis itself, and of discovering the elements therein which are the most important to know, and which this science should always preserve: these fundamental elements are those which are reproduced in all natural effects”. Discours Preliminaire (page xxii)

Jean Baptiste Joseph Fourier was born at Auxerre on March 21, 1768, and died at Paris on May 16, 1830. He was the son of a tailor, and was educated by the Benedictines. The commissions in the scientific corps of the army were, as is still the case in Russia, reserved for those of good birth, and being thus ineligible he accepted a military lectureship on mathematics. He took a prominent part in his own district in promoting the revolution, and was rewarded by an appointment in 1795 in the Normal school, and subsequently by a chair in the Polytechnic school. Fourier went with Napoleon on his Eastern expedition in 1798, and was made governor of Lower Egypt. Cut off from France by the English fleet, he organized the workshops on which the French army had to rely for their munitions of war. He also contributed several mathematical papers to the Egyptian Institute which Napoleon founded at Cairo, with a view of weakening English influence in the East. After the British victories and the capitulation of the French under General Menou in 1801, Fourier returned to France, and was made prefect of Grenoble, and it was while there that he made his experiments on the propagation of heat. He moved to Paris in 1816. In 1822 he published his Théorie analytique de la chaleur, in which he bases his reasoning on Newton’s law of cooling, namely, that the flow of heat between two adjacent molecules is proportional to the infinitely small difference of their temperatures. In this work he shows that any functions of a variable, whether continuous or discontinuous, can be expanded in a series of sines of multiples of the variable – a result which is constantly used in modern analysis. Lagrange had given particular cases of the theorem, and had implied that the method was general, but he had not pursued the subject. Dirichlet was the first to give a satisfactory demonstration of it.

Fourier left and unfinished work on determinate equations which was edited by Navier, and published in 1831; this contains much original matter, in particular there is a demonstration of Fourier’s theorem on the position of the roots of an algebraic equation. Lagrange had shown how the roots of an algebraic equation might be separated by means of another equation whose roots were the squares of the differences of the roots of the original equation. Budan, in 1807 and 1811, had enunciated the theorem generally known by the name of Fourier, but the demonstration was not altogether satisfactory. Fourier’s proof is the same as that usually given in textbooks on the theory of equations. The final solution of the problem was given in 1829 by Jacques Charles François Sturm (1803–1855).

James Clerk Maxwell


In 1962 Thomas Kuhn wrote a treatise on the philosophy of science entitled “The Structure of Scientific Revolutions”. The central theme of this classic work is that science works by agreeing on world views or paradigms which describe the laws, the rules and the assumptions of science. When a scientific paradigm fails to account for new observations, there needs to be a “paradigm shift” to a new view of the world. In general paradigm shifts take quite a while to occur, primarily because the existing paradigm is entrenched in the scientists of the day. Typically, young newcomers, who do not have as strong a commitment to the paradigm as their elders, take up a new idea and try to accomplish a paradigm shift. This may take as long as a generation – perhaps 20 to 25 years – until the previous generation has left the scene.

The story of the paradigm shift associated with the work of James Clerk Maxwell exemplifies this effect very well.

  • 1873: Maxwell’s treatise is published
  • 1873 – 1885: Maxwell’s work is largely ignored except by a small group of workers.
  • 1879: Maxwell dies
  • 1884: Oliver Heaviside expresses Maxwell’s Equations as we know them today
  • 1888: Maxwell’s wave theory verified by Hertz
  • 1890’s: Maxwell’s theory begins to gain wide acceptance

It is indeed a curious footnote to the history of science that Maxwell didn’t live long enough to see Maxwell’s Equations, as we know them today.

Among physicists the Scottish mathematician has a reputation exceeded only by Newton and Einstein. He was educated at Edinburgh and Cambridge University. During investigations of color vision at Cambridge he found quantitative equations for the amount of red, green and blue light needed to reproduce a particular color (the same method used to produce different colors on computer screens). In 1856, he published a paper on the stability of Saturn’s rings. In two papers in 1859-60, he extended Clausius’s work on the kinetic theory of gases. In 1868, he published a paper analyzing (steam) governors, which is regarded as the foundation of control theory (cybernetics). In 1870, in a paper called `On Hills and Dales’, he started the branch of mathematics now called global analysis. From 1871, he was Cavendish Professor of Experimental Physics at Cambridge, where he was responsible for designing the famous Cavendish laboratory. In 1878, he returned to gas theory, and extended Boltzmann’s extension to his own earlier theory.

This would have been enough to assure his place among the great nineteenth century physicists, but his major theoretical work was on electricity and magnetism. In 1861-2, he used Faraday’s cell model to derive equations to describe electro-magnetic properties. One of the predictions was the existence of electro-magnetic waves travelling at the speed of light. In 1864 he presented what are now known as Maxwell’s equations, stripped of the mechanical cell model that Faraday had used.

The Kinetic Theory of Gases

The kinetic theory of gases attempts to predict the properties of gases mathematically by assuming that a gas is composed of randomly moving molecules. In the simplest model, these molecules behave like mathematically elastic billiard balls. The temperature of a gas is related to the average speed (actually the average square of the speed – i.e. the total kinetic energy) of its molecules. Not all the molecules will move at the same speed, but they should be mixed randomly so that the temperature is the same throughout the gas. Maxwell proposed a distribution of molecular velocities (it was derived mathematically later by Boltzmann, and is now called the Maxwell-Boltzmann distribution) to account for the observed properties.

Maxwell’s Demon

Maxwell’s Demon was a thought-experiment, introduced in the 1870 textbook `The Theory of Heat’. The demon cannot do work, but is able to open and shut a valve to sort the molecules, concentrating the faster moving ones at one end of a tube, and the slower moving ones at the other. The result is to produce a higher temperature at one end than the other. This of course never happens, and contravenes the Second Law of Thermodynamics, which, as a principle, has been tested for many years and never found false. Maxwell decided that there are so many more ways for the molecules to be evenly than unevenly distributed (with regard to their speeds), that uneven distributions never occur in practice.


An excited atomic state with a 10-year lifetime

An excited atomic state with a 10-year lifetime has been discovered in the ytterbium atom, raising hopes for atomic clocks 1000 times more accurate than now possible. The Heisenberg uncertainty principle states that the longer a system can be observed, the smaller the uncertainty in its energy can be; therefore, it is extremely desirable to tune an atomic clock to a long-lived high-energy (excited) state. Researchers at the National Physical Laboratory in the UK laser cool and trap a single ytterbium ion. They then use a laser photon to boost the atom’s outermost electron to the long-lived state. With additional laser light, the researchers subsequently induce the electron to return to its lowest-energy (ground) state. By noting the characteristics of the laser light interacting with the electron, the researchers determine a 3700-day lifetime for the state. In addition to being the longest living excited energy state yet detected in an atom, it is the first observed “octupole” transition, a very rare transition in which the electron changes its angular momentum by a relatively large amount of three units. Once in this state, the electron (in the absence of external perturbations) can only decay via the octupole transition, which is why the state lasts so long. An atomic clock based on the transition would be very precise but requires much additional development. (M. Roberts et al., Physical Review Letters, 10 March 1997; see also Nature, 20 March 1997.)

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