VOL. 22 September ISSUE YEAR 2021

Off the Beaten Track

in Vol. 22 - September Issue - Year 2021
Red And Violet
Frederick William Herschel

Frederick William Herschel

The electromagnetic spectrum

The electromagnetic spectrum

The audience sat in stunned silence as the last notes reverberated off the chapel walls. Rarely had they heard such a moving composition, the rich texture of notes cascading from the organ pipes high above. The composer was pleased with his work. The faintest hint of a smile briefly appeared on his lips as he rose to take a bow.


Friedrich Wilhelm Herschel and Johann Wilhelm Ritter were two German scientists and philosophers, born and raised during the Enlightenment, a period of intellectual and philosophical ferment that swept across Europe during the seventeenth and eighteenth centuries. Both men excelled in various branches of the sciences and the arts. Among their many achievements, they are remembered for two important scientific discoveries: infrared light and ultraviolet light.
Friedrich Wilhelm Herschel was born in Hanover in 1738. Inheriting a love for music from his father, Herschel joined the Hanover Military Band as an oboist as a teenager. He quickly learned to play the violin, the harpsichord and the organ. At the age of twenty, Friedrich was sent by his father to live in England and changed his name to Frederick William Herschel. His musical career took off and Herschel composed over two hundred symphonies, concertos and works for various instruments. He performed many of his works himself in chapels and concert halls across Great Britain. In 1780 he was appointed director of the Bath Orchestra.
Herschel also took an interest in natural philosophy, engaging “philosophical gentlemen” in lively discussions. In 1779 he was invited to join the Bath Philosophical Society and in 1785 he was elected a member of the American Philosophical Society in Philadelphia.
His interest in music and philosophy led him to read two books by an author called Robert Smith: Harmonics, or the Philosophy of Musical Sounds and A Compleat System of Opticks, which explained how to build telescopes. He studied books on astronomy, trigonometry, optics and on the principles of mechanics. He took lessons from a mirror-builder and was soon building his own telescopes. In the course of the following decades Herschel discovered over 800 double- or multiple- star systems. In March 1781, he discovered the planet Uranus and shortly thereafter, two of its moons. He was elected a Fellow of the Royal Society and appointed the King’s Astronomer.
In 1800, while trying to find the best color for a filter that would allow him to safely view the Sun, Herschel noticed that filters of different colors generated different amounts of heat. He passed the sunlight through a prism in order to break down the light into a color spectrum. He then measured the temperature of each color by placing a thermometer on it. Indeed, the temperature rose steadily going from violet to red, but Herschel noticed that the increase did not seem to stop at the red end. On a hunch, he placed a thermometer next to the red color in the spectrum where there was no visible color and, sure enough, he got a temperature that was higher than that of the red color. Conscious of the oxymoron, he concluded that there must be a source of “invisible light” that generated more heat than that generated by the red end of the color spectrum. By adding the Latin prefix “infra” (below), the word “infrared” was coined.
Johann Wilhelm Ritter was born in Prussia in 1776. He was a chemist, physicist and philosopher. At the age of fourteen, he became an apprentice apothecary and studied the physiological effects of electricity generated by chemical reactions. In 1800 he discovered that water could be decomposed with electricity and was able to accurately measure the amounts of hydrogen and oxygen generated in the reaction. Between 1801 and 1802, he invented the process of electroplating and built an electrochemical cell. Strongly influenced by the philosophical outlook of Naturphilosophie, Ritter was constantly searching for polarities in the forces of nature. When he heard about Herschel’s discovery of infrared heat radiation, he wondered whether there could be an opposite force at the other (violet) end of the color spectrum. After several failed attempts to find a “cooling” source of radiation, he discovered that silver chloride transformed faster from white to black when placed next to the darker, violet end of the color spectrum. As this effect was not produced by any visible light, Ritter posited the existence of “chemical rays”. By adding the Latin prefix “ultra” (beyond), this radiation was later called “ultraviolet”.

By Giovanni Gregorat, Contributing Editor MFN