Why is the Sky Blue? – John Tyndall

“The brightest flashes in the world of thought are incomplete until they have been proven to have their counterparts in the world of fact.”
– John Tyndall

John Tyndall. Photograph by Barraud.John Tyndall. Photograph by Barraud. Courtesy of The Wellcome Library (CC BY-NC 2.0)

Today we are celebrating the birth of one of the most important scientists and educators of the19th century, John Tyndall. The Irish physicist was born on this day in 1820 and is remembered by many as the man who first explained why the sky is blue. This discovery, known as the Tyndall effect, proves the sky’s blue colour results from the scattering of the Sun’s rays by molecules in the atmosphere.

Sisal plantations near Muheza, TanzaniaSisal plantations near Muheza, Tanzania. Courtesy of The Wellcome Library (CC BY-NC 2.0)

Tyndall’s major scientific contributions were in physical chemistry, initially with the study of diamagnetism, and then thermal radiation – producing a number of discoveries in atmospheric processes. His experimental physics and resulting discoveries were brought to a wider audience through the publication of seventeen books during the 19th century. Many of these,such as Sound: A Course of Eight Lectures delivered at the Royal Institution of Great Britain can be found through Europeana. 

Tyndall's apparatus for experimentsTyndall’s apparatus for experiments disproving doctrine of spontaneous generation, used here as a culture chamber. Courtesy of The Wellcome Library (CC BY-NC 2.0)

Other major experiments from Tyndall include the transmission of both radiant heat and light through various gases and vapours. Tyndall discovered that water vapour absorbs much more radiant heat than the gases of the atmosphere and argued the consequent importance of atmospheric water vapour in moderating the Earth’s climate—that is, in the natural greenhouse effect. He is also credited with the first ever atmospheric pollution measurements using infra-red and scattering measurement instruments, showing that ozone, the upper layer of atmosphere, is vital to life on Earth, and it is an oxygen cluster rather than a hydrogen compound. 

Professor Tyndall demonstrating a fog-horn to Queen VictoriaProfessor Tyndall demonstrating a fog-horn to Queen Victoria and her entourage. Courtesy of The Wellcome Library (CC BY-NC 2.0)

Tyndall laid significant groundwork in physics for magnetism, electricity, molecular physics, optics, sound, the properties of materials, diamagnetism and heat.

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