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Lord Rayleigh: The Noble Laureate

Updated on August 24, 2012
Rayleigh scattering is what gives the sky its blue color.
Rayleigh scattering is what gives the sky its blue color. | Source
Terling Place, seat of the Baron Rayleigh in Essex
Terling Place, seat of the Baron Rayleigh in Essex | Source

The name Rayleigh appears quite often in the study of physics and other scientific disciplines. Rayleigh scattering refers to the scattering of photons in the atmosphere that turn the daytime sky blue. Rayleigh waves are a type of surface wave generated by an earthquake. Rayleigh fading is a useful model for predicting wireless signal strength in urban areas. One is compelled to wonder just who this Rayleigh person was and how he managed to get his name on so many scientific concepts.

In fact, Rayleigh is not a person at all but a title of nobility. The Barony of Rayleigh was created in 1821 for Charlotte Mary Gertrude Strutt, daughter of the Duke of Leinster and wife of Joseph Strutt, member of a prominent Essex family who'd earned their fortune in the milling industry.

While it took an act of the British Monarch to establish the Rayleigh name, it was the work of Charlotte and Joseph's grandson John William Strutt that later enshrined the name in scientific history. Among many honors and accolades he received over a lifetime of scientific research, Strutt was awarded the Nobel Prize in 1904 for discovering the element argon.

John William Strutt, 3rd Baron of Rayleigh
John William Strutt, 3rd Baron of Rayleigh | Source

"One's instinct at first is to try to get rid of a discrepancy, but I believe that experience shows such an endeavour to be a mistake"

- Lord Rayleigh, 1895

John William Strutt

John William Strutt was born on November 12, 1842, the oldest son of John James Strutt, the 2nd Baron Rayleigh.

Poor health during his youth and childhood held Strutt back in his education, as he was frequently absent from school. However, he had a remarkable intellect that allowed him to catch up quickly. Enrolling at Trinity College in Cambridge in 1861, he excelled at mathematics and graduated with top honors.

It was at Cambridge that the young Strutt began to cultivate an interest in science. At the time, a career in science was not considered an appropriate vocation for a future member of the nobility. However, Strutt was determined to pursue his scientific endeavors. In 1866, he was elected to a Fellowship at Trinity where he could continue his research work.

Being a member of the privileged class had its advantages for the young Strutt. Since he did not need to earn an income as a professor due to his family's wealth, he was able to devote his full time to research - including setting up a scientific laboratory on his family estate in Essex. There he began his work on electromagnetics and optics, and in 1871 published his theory on the scattering of light that we now know as Rayleigh scattering.

In the same year, Strutt married Evelyn Balfour. She was the sister of Arthur James Balfour, a friend Strutt had met at Cambridge who would later become Prime Minister. Not long after the wedding, Strutt became ill with rheumatic fever. Doctors advised him to travel to Egypt to recuperate, and he spent the winter of 1872-1873 sailing on the Nile before returning to England.

It was during this trip to Egypt that Strutt began working on The Theory of Sound, one of his most famous scientific works. This would eventually be published as a two-volume set of textbooks that explained in depth the mechanics of sound production and acoustic wave propagation. The Theory of Sound was a seminal work in the study of acoustics and is still used by acoustic engineers today.

Upon the death of his father in 1873, Strutt inherited his title as the Third Baron Rayleigh. Now Lord Rayleigh, he also inherited management responsibility for the family's 7,000-acre estate in Essex. For a few years, he tried to manage the estate's affairs while continuing to conduct his research. However, the demands of running the farm - and the economic depression in the British agricultural sector - made it difficult for Lord Rayleigh to continue his scientific research. In 1879, Lord Rayleigh accepted a prestigious position as the Cavendish Professor of Experimental Physics at Cambridge, turning over management of the family estate to his younger brother.

While serving as Cavendish Professor, Lord Rayleigh set about improving the laboratory at Cambridge and establishing it as a teaching and research institution. He also developed laboratory courses in multiple disciplines of physics, allowing students to learn by experiment rather than lecture.

Although his tenure at Cambridge was a successful one, by 1884 Lord Rayleigh was eager to return to his laboratory in Essex and continue his independent research. During this period, he wrote some of his most important papers on a wide variety of topics, ranging from the mechanics of bird flight to the propagation of earthquake waves to methods for reproducing colors by photograph. It was also during this period that Lord Rayleigh made the most significant advance of his career - the discovery of argon.

Apparatus used for isolating argon.
Apparatus used for isolating argon. | Source

The Discovery of Argon

In 1893, while conducting experiments to understand the properties of nitrogen gas, Rayleigh encountered a frustrating anomaly. He'd used two slightly different methods for isolating nitrogen - one that simply passed air through a red-hot copper pipe to remove the oxygen and hydrogen, and a second method that bubbled the air through liquid ammonia first. Rayleigh found that the nitrogen bubbled through ammonia was less dense than the nitrogen extracted from air alone.

Though the difference in density was small - just one half of one percent - it was odd, and too large to be explained by margin of error. The difference seemed to be in the gas itself - nitrogen produced solely from air was heavier than nitrogen extracted from ammonia. This made no sense, however - how could one element have two different densities? From this Rayleigh then arrived at a more plausible explanation: another gas was mixed with the nitrogen, and one that did not react chemically with other atmospheric gases.

In order to isolate this strange, non-reactive gas, Lord Rayleigh devised an experiment based on the method used by British scientist Henry Cavendish to isolate hydrogen more than a century before. His apparatus consisted of an upended test tube full of air (A, in the diagram at right) partially submerged in a jar of weak alkali (B). An electric current was applied to the air in the test tube using platinum-tipped wires (D) that passed through two U-shaped tubes (C) that had been filled with mercury to prevent contamination by outside air.

Lord Rayleigh was also collaborating with Scottish chemist Sir William Ramsay on the problem. Sir Ramsay had devised an alternative method of isolating the non-reactive component of nitrogen by bubbling the gas through sulfuric acid and then running it over red-hot magnesium, forming magnesium nitride. The gas that remained once all the nitrogen had been removed was found, as predicted, to have no chemical reactions to any other elements. It was also determined to have an atomic weight of 39.9, putting it squarely between potassium and chlorine on the still-developing Periodic Table of the Elements.

Sir Ramsay and Lord Rayleigh had discovered a new element. They decided to name it argon, after the Greek argos meaning "lazy" or "inactive." They jointly published their findings in the Proceedings of the Royal Society of London in 1895, and were awarded the 1904 Nobel Prize in Physics for their work.

A Lifetime of Achievement

John William Strutt, the 3rd Baron Rayleigh, died in 1919 at age 76, leaving a legacy of several lifetimes-worth of scientific discovery. In total, he wrote nearly 450 papers and books, presented countless lectures, and radically changed the way science was taught at institutions of higher learning. Lord Rayleigh's oldest son Robert Strutt, the 4th Baron Rayleigh, also inherited his curiosity and love of science and achieved a number of important discoveries in physics, geology, and atmospheric science. Craters on the Moon and Mars bear his name, as does a main-belt asteroid. Though Lord Rayleigh was presented numerous awards and medals in his lifetime, perhaps his greatest reward is the knowledge about our world that he left behind.


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