Miscellaneous

The People Behind the Equations – John William Strutt (Baron Raleigh)

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John William Strutt (1842-1919), better known by his title Baron Raleigh, was one of the last great multi-disciplinary scientists. He was born into an aristocratic family in Witham in the English countryside, about 70 km north-east of London. He was fortunate to survive numerous close shaves with death while growing up: he was nearly shot while at a firing range, fell into a pond while playing with his dog, and then had a persistent illness which got him sent home from the prestigious Eton boarding school. Eventually he ended up getting some private tutoring and made it into Cambridge for mathematics in 1861. He would graduate first in his class after completing the infamously tough Tripos exams.

In 1873 Strutt’s father died and he inherited the property and the title of Baron Raleigh. He could easily have decided to go home and live off the family inheritance, but would have none of that. He immediately had a laboratory built in his family estate. When he later became a professor at Cambridge, he bought a second set for there too. In a time where theory and practice were often separated, Rayleigh insisted on including hands-on labs and experiments in the classes he taught.

Rayleigh pioneered the art of dimensional analysis – by playing around with the dimensions of particular units, he could often come up with dimensionless numbers from which he could draw conclusions about what certain variables are proportional to. Famously, he showed that the intensity of light scattering is proportional to the fourth power of its wavelength, which is why this phenomenon is now known as Rayleigh scattering. Since the wavelength of red light is about 1.5 times that of blue light, blue light will be scattered at roughly five times the intensity of red. In this way, Rayleigh explained the age-old mystery of why the sky is blue.

Together with the chemist William Ramsay, Rayleigh discovered a new element by accident while having trouble determining the mass of air. It eventually occurred to the two scientists that there was a gas other than nitrogen and oxygen in the air interfering with their calculations. The new gas didn’t seem to react with anything else, unlike any other element previously discovered. After futilely trying to get the gas to react, they decided to name the gas “argon”, which is Greek for “lazy”. In 1904, both men were awarded Nobel Prizes for the discovery.

Throughout his career, Rayleigh worked on numerous other problems with practical applications; he did research in acoustics, free convection, heat transfer, fluid flow in a pipe, optics and refraction, and electromagnetism. Among other discoveries, he found that the Earth’s rotation does not cause light refraction, derived the dimensionless Rayleigh number which determines the mode of heat transfer (convection or conduction) in a free convection flow, and developed one of the earliest devices to accurately measure electrical resistance.

Today, nearly a century after his death, Baron Rayleigh’s legacy has been immense. The discovery of argon would cause chemists to start looking for other ‘lazy gases,’ and it was not long after that an 18th column was added to the Periodic Table. Explaining the unexpected results of Rayleigh’s refraction experiments would eventually cause Lorentz and Einstein to develop relativity theory. Rayleigh’s electrical measurements would lead to the ohm and ampere being officially defined as SI units. Dimensional analysis would prove to have many applications in fluid mechanics, such as testing prototypes in wind tunnels. Science and engineering owe him a huge debt.

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