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One year later, at the age of 38, Doppler gave a lecture to the Royal Bohemian Society of Sciences and subsequently published his most notable work, Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels ("On the coloured light of the binary stars and some other stars of the heavens"). There is a facsimile edition with an English translation by Alec Eden. ^[1] In this work, Doppler postulated his principle (later coined the Doppler effect) that the observed frequency of a wave depends on the relative speed of the source and the observer, and he later tried to use this concept for explaining the visible colours of binary stars (this hypothesis was later proven wrong). (1)

My additions

As a young boy, Doppler showed promise for his family's trade. However, his small frame and his delicate physique was not meant for the work of a stone mason. When his father realized that Christian was not cut out for the family trade, he instead pushed him to pursue a career in commerce. This lead to his mathematical ability being discovered by the mathematician Sion Stampfer, whose assessment of Doppler lead him to attend the Polytechnic Institute in Vienna at the age of 17. ^[2]

(1) Doppler believed that if a star were to exceed 136,000 kilometers per second in radial velocity, then it would not be visible to the human eye. ^[3] However, what Doppler believed was only partially true, as stars also have their own inherent color. ^[4]

Doppler did not have any experimental evidence of his principle so it did not receive much attention from anyone outside of his colleagues at first. ^[3]

In 1845, the first demonstration of the Doppler effect would occur in Utrecht, Holland. The demonstration was performed through participants on a train that would pass by a group of musicians, in which they were able to observe a notable difference in the sound when approaching and passing by the musicians. ^[4]