Picture of Christian Doppler
The University of St. Andrews, Scotland
Christian Doppler was an Austrian mathematician who lived between
1803-1853. He is
known for the principle he first proposed in Concerning the coloured
light of double stars
in 1842. This principle is now known as the
. He hypothesised that the pitch of a sound would change if
the source of the sound was moving.
Doppler's hypothesis was tested by Buys Ballot in 1845. He used two sets of trumpeters: one set
stationary at a train station and one set moving on an open train car.
Both sets of musicians had perfect pitch and held the same note. As the
train passed the station, it was obvious that the frequency of the two
notes didn't match, even though the musicians were playing the same
note. This proved Doppler's hypothesis.
Later, a scientist named Fizeau generalized Doppler's work by applying his
theory not only to sound but also to light.
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