Astronomers had begun using photographic plates on telescopes, and Vogel adapted that new technology to the radial velocities problem. Using the human eye to observe the spectral lines was the chief problem. Vogel was also working to improve the measurements of the radial velocity of stars-the speed along the line of sight-and was acutely aware that the many values quoted by Huggins and others for stellar velocities were nearly the same as the uncertainties in the measurement process. Despite such demonstrations, Petzval was never satisfied, and over the succeeding years Mach had to contend with persistent confusion and disbelief by many others until he finally refused to discuss the effect further. That arrangement demonstrates even Petzval’s preferred principle of frequency conservation. 1 In response, Mach devised an even more ingenious apparatus, which allows one to listen in one direction to the rising and falling tones and in an orthogonal direction, in which the reed and observer are relatively stationary, to a constant pitch. 6 Petzval continued denying the effect and accused Mach of youthful foolishness and of throwing away his chances at a career by pursuing an abandoned theory. As the device spun, the reed approached and receded from the observer, who could hear the rapidly rising and falling tones. Mach built and tested a rotating-reed system with tubing that delivered air to the reed, causing it to vibrate at its natural frequency while directing its sound to a stationary observer. ![]() Several years later, he suggested to his student Ernst Mach that he construct a laboratory apparatus to directly demonstrate the acoustic Doppler effect. That might have been the end of the affair at the Physics Institute of Vienna, but Ettingshausen wasn’t ready to abandon the Doppler effect just because a committee said it didn’t exist. Ernst Mach later said that Doppler would agree but quipped that if the orchestra were falling from a great height, the audience would hear the piece in F major rather than E major. He argued that the pure notes of a well-tuned orchestra would be just as harmonious to an audience on a blustery day as on a calm one the notes would be unaffected by the wind’s motion. Petzval conflated a source and receiver in relative motion with a stationary source and receiver embedded in a moving medium. Although he was a mathematician of some talent, he was adrift as a natural philosopher. From that premise, he proposed a principle for the conservation of oscillation time in undulatory phenomena. ![]() Petzval thought that no great science could come from a few simple lines of algebra: In his view, all natural phenomena were the manifestations of underlying differential equations. Petzval’s speech, which was published later, attacked Doppler’s theory for both sound and light. The large audience for the mock trial of the Doppler effect stands in ironic contrast to the mere five members of the Bohemian Society who first heard Doppler’s ideas 10 years earlier. At a later meeting on, about 60 members and guests assembled to hear both sides of the argument. Petzval’s attackĪt a meeting of the academy on 22 January 1852, Petzval read a paper criticizing Doppler’s theory. ![]() 1 Buys Ballot published a paper describing the experiment, 4 but he still refused to acknowledge that light could change color despite the close analogy between sound and light. The experiment validated Doppler’s theory for sound. That time, with Buys Ballot riding the footplate of the locomotive and the car of trumpeters holding a steady note, musicians standing beside the tracks could hear the approaching note a half-tone higher and the receding note a half-tone lower. Unfortunately, the musicians were pelted with hail and snow, which prevented them from blowing their horns properly, so the experiment was reconvened in the milder month of June. Buys Ballot did not think that stars would change color by moving, but having no means to test the effect on light, he decided to test it on sound. ![]() Subsequently, on a cold February morning in 1845, Dutch scientist Christoph Buys Ballot, who had recently received his doctorate from the University of Utrecht, loaded an open train car with seasoned musicians and sent them blowing their horns down the railroad line between Utrecht and Maarssen. Many who heard of Doppler’s theory did not believe it.
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