Christian Doppler

Whose Principle Rode a Railway Carriage · Physicist & Mathematician · 1803–1853

The poor, overlooked Prague teacher who worked out that motion changes an observed frequency — right about the principle, wrong about the coloured stars he invented it to explain.

Who was Doppler?

Christian Doppler was born in Salzburg in 1803 into a family of stonemasons and was too frail for the trade, so he was pushed towards mathematics instead. For years he could not obtain an academic post at all, worked as a bookkeeper, and was on the point of selling up and emigrating to America when a position in Prague finally came through. In 1842 he read a paper to the Royal Bohemian Society arguing that when a source of waves and an observer move relative to one another, the observed frequency must change: approach crowds the waves together and raises the pitch, recession stretches them out and lowers it. Because the argument is geometrical rather than a claim about any particular medium, he asserted it must hold for light as well as sound, and he proposed it as the explanation for why some double stars appear coloured. That application was wrong — the velocities of stars are far too small to shift their apparent colour appreciably — and he was attacked for it, notably and at length by his colleague Josef Petzval. The principle itself was entirely right. In 1845 Christoph Buys Ballot tested it properly in the Netherlands by putting a band of trumpeters on an open railway carriage and stationing musicians with perfect pitch on the platform to write down the notes as the train passed. The pitch fell exactly as predicted. Doppler taught Gregor Mendel in Vienna and encouraged his use of experimental statistics. He died of a lung disease at forty-nine.

Major achievements

• Stated in 1842 that relative motion changes the observed frequency of a wave
• Argued the effect from geometry, so that it must apply to light as well as sound
• Was confirmed by Buys Ballot's railway experiment in 1845
• Taught Gregor Mendel and encouraged his statistical approach to experiment
• Became the first director of the Institute of Physics in Vienna

Life in brief

• 1803 — Born in Salzburg: To a family of stonemasons; too frail for the trade.
• 1835 — Nearly emigrates: Unable to get a post; on the point of leaving for America.
• 1842 — The Prague paper: Relative motion changes an observed frequency — for sound and light alike.
• 1845 — Buys Ballot's test: Trumpeters on a railway carriage confirm the sound prediction.
• 1847 — Teaches Mendel: Encourages a young friar towards statistics in experiment.
• 1850 — Institute of Physics, Vienna: Becomes its first director.
• 1853 — Dies in Venice: Of a lung disease, at forty-nine.

Explore the life of Doppler — five chapters

1. Too Frail for the Trade — A stonemason's son, and years without a post
2. Crowding and Stretching — The principle, argued from geometry alone
3. The Thing He Wrote the Paper to Explain — Double stars, and an application that fails
4. Trumpeters on an Open Railway Carriage — Buys Ballot's test, 1845
5. The Red Shift — Mendel, an early death, and an expanding universe

Read the five-chapter life of Christian Doppler →

Where Doppler appears in your course

Christian Doppler has a genuine claim on 2 lessons of the Pearson Edexcel International GCSE science course built into Incandio:

• The Doppler Effect — Physics: This page is his 1842 paper, read to the Royal Bohemian Society by an underpaid teacher who had nearly emigrated to America for want of a post. He reasoned it purely from the geometry of the wavefronts — approach crowds them, recession stretches them — and published without ever having measured it. The test came in 1845, when Christoph Buys Ballot hired a locomotive, put a band of trumpeters on an open carriage holding a steady note, and stationed musicians with perfect pitch along the platform to write down what they heard as the train went past. The pitch fell exactly as predicted. He is the right person to ask what it is like to publish a bold general claim and then wait for someone else to find out whether it is true.
• Red-Shift — Physics: Statement 8.15 is Doppler's 1842 paper, and it is a useful case because he was right about the principle and wrong about the very thing he wrote it to explain. He argued from the geometry of the wavefronts that motion must change the observed frequency, and insisted that since this is geometry rather than a fact about any particular medium it must hold for light as well as sound. He then proposed it as the reason some double stars appear coloured, which is false — stellar velocities are far too small to shift a star's apparent colour. Buys Ballot tested the sound prediction in 1845 with trumpeters on an open railway carriage, confirmed the principle, and rejected the application.

Begin

• Start a conversation with Doppler — a dramatised, historically grounded AI portrayal
• Read the Historical Brief
• Explore the life of Doppler — five chapters
• Find your exam topics · Meet all 208 figures