Christian Doppler

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Christian Doppler.

Johann Christian Andreas Doppler (November 29, 1803 – March 17, 1853) was an Austrian mathematician and physicist, most famous for the hypothesis of what is now known as the Doppler effect which is the apparent change in frequency and wavelength of a wave that is perceived by an observer moving relative to the source of the waves.

Life

Christian Doppler was born in Salzburg, Austria, as the son of a well-to-do stone-mason, Johann Evangialist Doppler and his wife, Therese. A baptismal certificate indicates that Doppler was christened "Christian Adreas." Doppler was not of strong constitution, and did not follow his father into the construction trades. Instead, he was allowed to follow an academic track. His father asked the advice of Simon Stampfer, a local educator, as too the boy's future. Stampfer recognized Doppler's potential and recommended that his father send him to Vienna.<<<Maulik, Dev. 1997. Doppler ultrasound in obstetrics & gynecology. New York: Springer. 2. ISBN 0387942408.>>> After completing high school he spent three years at the Polytechnic Institute in Vienna, and returned to Saltzburg, where he completed his studies while tutoring mathematics and physics. He returned to the Polytechnic Institute for four years, where he taught higher mathematics. It was during this period that he wrote his first papers in mathematics and electricity.

Relative speed and the frequency of light

Unable to find a teaching position, he contemplated a move to the United States. But after making preparations for the trip, he unexpectedly secured a post in 1835 as professor of mathematics and accounting at the State Secondary School in Prague. In 1841, he was employed at the State Technical Academy as a mathematics professor. A year later, in 1842, he read his first work on the changes in frequency of waves through a medium measured by an observer moving with respect to the waves' source. This has come to be known as the Doppler effect. The paper, presented before the Royal Bohemian Society of Sciences on May 25, 1842, was entitled On the colored light of the double stars and certain other stars of the heavens.<<<Hennerici, M., and Stephen P. Meairs. 2001. Cerebrovascular ultrasound theory, practice, and future developments. Cambridge: Cambridge University Press. 88.>>> His work was an extension of that of James Bradley, the eighteenth century astronomer who measured the speed of light by noting the abberation that affects the apparent positions of all stars due to the orbital motion of the earth. Bradley made his calculations assuming a particle theory of light. But Doppler applied similar reasoning to show that the frequency of light would change if the observer was not stationary relative to the light source.

Doppler's work was later published under the title: On the colored light of the binary refracted stars and other celestial bodies - Attempt of a more general theory including Bradley's theorem as an integral part. In Doppler's own words, "...nothing seems to be more intelligible than that to an observer the path length and the interim durations between two consecutive breakings of a wave must become shorter if the observer is hurrying toward the oncoming wave, and longer if he is fleeing from it..." As the frequency is dependent on the number of beats per unit time, and in light is related to the color perceived, Doppler concluded that the red color of some stars demonstrates that the perceived wavelength is greater as a result of the star and the earth moving away from each other."<<<Schuster, Peter. 2005. Moving the stars Christian Doppler, his life, his works and principle, and the world after. Pöllauberg, Austria: Living Edition. 63.>>>

Besides light, Doppler also mentioned sound in his 1842 work. In this work, Doppler tried to explain the color of binary stars by conjecturing that if the earth and the binaries are rapidly approaching each other, their color should be shifted to the shorter, or violet, end of the spectrum, while if receding, to the red, or longer wave-length, end. He assumed that the normal light from all stars was light, and that any deviation was due to the relative velocity between the star and the observer.

Two investigators, Buys Ballot in 1845 and John Scott Russell in 1848, verified Doppler's prediction with respect to sound. But the former also criticized Doppler's assumptions about starlight. Doppler responded to these objections with several papers of his own. Still, in 1847, the Italian astronomer Benedict Sestini published a catalogue of star colors, and addressed some of Doppler's ideas. Doppler's contention about starlight was shown to be incorrect, however. Relative speed between the observer and the light source would shift all colors equally, resulting only in special cases in a change in color. Furthermore, a color change, if it were to occur, would be so slight as to be undetectable by the eye.

Some of these points were made in a presentation by H. Fizeau in 1848, who applied Doppler's theory to the total shift in the position of so-called Fraunhofer lines that appear in spectra and that mark specific frequencies of light.

Doppler did not always take kindly to criticism of his ideas. He is said to have defended some of his positions to only little effect.

Doppler, however, went on to elaborate on his theory and published numerous papers on a variety of subjects throughout his career. In 1843, he was made a full professor, and in 1846 he published equations applying to the case where both the observer and the wave source were in motion. Doppler was unsure regarding the application of his principle to transverse waves, where the undulatory motion is perpendicular to the direction of wave motion. This case was treated by the mathematical physicist B. Bolzano, who announced his findings in the same year that Doppler's paper appeared. Bolzano, who was a colleague of Doppler in Prague, predicted that Doppler's method would enjoy great utility in determining the velocity and other characteristics of stellar objects. <<<Merz, John Theodore. 1912. A history of European thought of the nineteenth century. Vol. 3. Edinburgh: Blackwood. 10.>>>

It is this application that was to mark the future application of Doppler's principle more than a shift in the actual color of stars. <<<Campbell, William Wallace. 1913. Stellar motions, with special reference to motions determined by means of the spectrograph. New Haven: Yale university press. 12-15.>>>

Also in 1846, Doppler calculated the resolution that could be obtained with a photographic plate, estimating that it was 40,000 times more suseptible to impressions than the human eye. He thus recommended that astronomers concentrate on magnifying the image made on a photographic plate instead of trying to increase the power of telescopes. <<<Anonymous. 1847. On the combination of the daguerrotype with the telescope. Civil Engineering and Architect's Journal. 10:102. Wiley and Putnam: New York.>>>

His research career in Prague was interrupted by the revolutionary incidents of March 1848, when he fled to Vienna. There he was appointed head of the Institute for Experimental Physics at the University of Vienna in 1850. During his presence at the University of Vienna, Doppler, along with Franz Unger, played an influential role in the development of young Gregor Mendel who later became the founding father of genetics. (Note: Gregor Mendel studied in the University of Vienna from 1851 to 1853. At that time, Doppler served as a professor there.)

He died from a pulmonary disease in Venice at age 49 on March 17, 1853. His tomb can be found just inside the entrance of the Venetian island cemetery of San Michele.

See also

• Light
• Sound

References

ISBN links support NWE through referral fees

<<Need at least 3 reliable references here, properly formatted.>>

• Schuster, Peter. 2005. Moving the stars Christian Doppler, his life, his works and principle, and the world after. Pöllauberg, Austria: Living Edition.; Webpage of the author)

• Alec Eden, "The search for Christian Doppler," Springer-Verlag 1992. (An English translation of Doppler's 1842 work on the Doppler effect can be found in this book. In this book, Alec Eden also made a detailed study regarding the full name of Christian Doppler. He believed that his full name should be "Christian Andreas Doppler".)

External links

• Christian Doppler and his birthplace in Salzburg
• John J. O'Connor and Edmund F. Robertson. Christian Doppler at the MacTutor archive
• Born between Salzburg and Braunau am Inn

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