In a series of brilliant experiments Heinrich Hertz discovered radio waves and established that James Clerk Maxwell’s theory of electromagnetism is correct.
Hertz also discovered the photoelectric effect, providing one of the first clues to the existence of the quantum world. The unit of frequency, the hertz, is named in his honor.
Heinrich Rudolf Hertz was born on February 22, 1857 in the German port city of Hamburg. He was the firstborn of five children.
His mother was Anna Elisabeth Pfefferkorn, the daughter of a physician.
His father was Gustav Ferdinand Hertz, an attorney who became a Senator.
His paternal grandfather, a wealthy Jewish businessman, had married into a Lutheran family and converted to Christianity.
Both of Heinrich’s parents were Lutherans, and he was raised in this faith. His parents, however, were more interested in his education than his religious status.
Aged six, Heinrich began at the Dr. Wichard Lange School in Hamburg. This was a private school for boys run by the famous educator Friedrich Wichard Lange. The school operated without religious influence; it used child-centered teaching methods, taking account of students’ individual differences. It was also strict; the students were expected to work hard and compete with one another to be top of the class. Heinrich enjoyed his time at school, and indeed was top of his class.
Unusually, Dr. Lange’s school did not teach Greek and Latin – the classics – needed for university entry. The very young Heinrich told his parents he wanted to become an engineer. When they looked for a school for him, they decided that Dr. Lange’s alternative focus, which included the sciences, was the best option.
Heinrich’s mother was especially passionate about his education. Realizing he had a natural talent for making things and for drawing, she arranged draftsmanship lessons for him on Sundays at a technical college. He started these aged 11.
Homeschool and Building Scientific Apparatus
Aged 15, Heinrich left Dr. Lange’s school to be educated at home. He had decided that perhaps he would like to go to university after all. Now he received tutoring in Greek and Latin to prepare him for the exams.
He excelled at languages, a gift he seems to have inherited from his father.
Professor Redslob, a language specialist who gave Heinrich some tuition in Arabic, advised his father that Heinrich should become a student of oriental languages. Never before had he met anyone with greater natural talent.
Heinrich also began studying the sciences and mathematics at home, again with the help of a private tutor.
He had a colossal appetite for hard work. His mother said:
When he sat with his books nothing could disturb him or draw him away from them.
Although he had left his normal school, he continued attending the technical college on Sunday mornings.
In the evenings he worked with his hands. He learned to operate a lathe. He built models and began constructing increasingly sophisticated scientific apparatus such as a spectroscope. He used this apparatus to do his own physics and chemistry experiments.
Architecture and the Army
Aged 17, Heinrich returned to school, the Johanneum, for a year in order to fully prepare for the classics exams for university. Having passed the exams, he promptly changed his mind again, deciding to become an architect’s apprentice. He moved to Frankfurt, where by day he worked in an architect’s office and in the evening he read physics books in German, and Ancient Greek literature in the original Ancient Greek – naturally!
Architecture quickly bored him.
In spring 1876, aged 19, he moved again, to Dresden, to study engineering. After only a few months he was drafted into the army for a year’s compulsory service. Although he enjoyed the discipline of army life, he found the army boring. Rather miserably, he wrote home at one point:
Meanwhile, his interest in mathematics and physics continued to grow.
Hertz’s Lifetime in Context
Becoming a Scientist
Physics in Munich
After completing his army service, the 20-year-old Hertz moved to Munich to begin an engineering course in October 1877. A month later, after much internal anguish, he dropped out of the course. He had decided that above all else he wanted to become a physicist.
He enrolled at the University of Munich, choosing courses in advanced mathematics and mechanics, experimental physics, and experimental chemistry.
After a successful year at Munich he moved to the University of Berlin because it had better physics laboratories than Munich.
Berlin, Helmholtz, and Recognition
In Berlin, aged 21, Hertz began working in the laboratories of the great physicist Hermann von Helmholtz.
Helmholtz must have recognized a rare talent in Hertz, immediately asking him to work on a problem whose solution he was particularly interested in. The problem was the subject of a fierce debate between Helmholtz and another physicist by the name of Wilhelm Weber.
The University of Berlin’s Philosophy Department, with Helmholtz’s encouragement, had offered a prize to anyone who could solve the problem: Does electricity move with inertia? Alternatively, we could frame the question in the form: Does electric current have mass? Or, as framed by Hertz: Does electric current have kinetic energy?
Hertz started work on the problem and quickly fell into a pleasant routine: attending a lecture each morning in either analytical dynamics or electricity & magnetism, carrying out experiments in the laboratory until 4pm, then reading, calculating, and thinking in the evening.
He personally designed experiments which he thought would answer Helmholtz’s question. He began to really enjoy himself, writing home:
In August 1879, aged 22, Hertz won the prize – a gold medal. In a series of highly sensitive experiments he demonstrated that if electric current has any mass at all, it must be incredibly small. We have to bear in mind that when Hertz carried out this work the electron – the carrier of electric current – had not even been discovered. J. J. Thomson’s discovery was made in 1897, 18 years after Hertz’s work.
The mass of 1.109 x 1030 humans would equal more than 30 solar systems like our own.
The electron’s mass is tiny indeed.
Other physicists began to notice just how dazzling Hertz’s work was – the young student put together experiments at the forefront of physics, personally modifying apparatus as needed. His practical skills, developed at home in the evenings, were proving to be priceless. His prize-winning work was published in the prestigious journal Annalen der Physik.
Recognizing the incredible talent he had in his laboratory, Helmholtz now asked Hertz to compete for a prize offered by the Berlin Academy: verifying James Clerk Maxwell’s theory of electromagnetism. Maxwell had stated in 1864 that light was an electromagnetic wave and that other types of electromagnetic wave could also exist.
Doctor of Physics
Hertz declined this project; he believed the attempt, with no guarantee of success, would take several years of work. He was ambitious and wanted to publish new results quickly to establish his reputation.
Instead of working for the prize, he carried out a masterful three-month project on electromagnetic induction. He wrote this up as a thesis. In February 1880, at the age of 23, his thesis brought him the award of a doctorate in physics. Helmholtz quickly appointed him as an assistant professor. Later that year Hertz wrote:
Hertz stayed in Helmholtz’s laboratory until 1883, during which time he published 15 papers in academic journals.
Mathematical Physics at Kiel
Hertz was a gifted experimental physicist, but competition to secure a lectureship at Berlin was high.
Instead, with Helmholtz’s support, Hertz became a lecturer in mathematical physics at the University of Kiel. This position, theoretical rather than experimental, extended his abilities. At Kiel he began to get to grips with Maxwell’s equations, writing in his diary:
The result of Hertz’s work was a highly regarded paper comparing Maxwell’s electromagnetic theory with competing theories. He concluded that Maxwell’s theory looked the most promising. In fact he reworked Maxwell’s equations into a more convenient form.
He later wrote:
The Discovery of Radio Waves
If you would like a somewhat more detailed technical account of Hertz’s discovery of radio waves, we have one here.
Well-Equipped Laboratories and Attacking the Greatest Problem
In March 1885, desperate to return to experimental physics, Hertz moved to the University of Karlsruhe. Aged 28, he had secured a full professorship. He was actually offered two other full professorships, a sign of his flourishing reputation. He chose Karlsruhe because it had the best laboratory facilities.
Wondering about which direction his research should take, his thoughts drifted to the prize work Helmholtz had failed to persuade him to do six years earlier: proving Maxwell’s theory by experiment.
Hertz decided that this mighty undertaking would be the focus of his research at Karlsruhe.
A Spark that Changed Everything
After some months of experimental trials, the apparently unbreakable walls that had frustrated all attempts to prove Maxwell’s theory began crumbling.
He discovered something amazing. Sparks produced a regular electrical vibration within the electric wires they jumped between. The vibration moved back and forth more often every second than anything Hertz had ever encountered before in his electrical work.
He knew the vibration was made up of rapidly accelerating and decelerating electric charges. If Maxwell’s theory were right, these charges would radiate electromagnetic waves which would pass through air just as light does.
Producing and Detecting Radio Waves
In November 1886 Hertz constructed the apparatus shown below.
He applied high voltage a.c. electricity across the central spark-gap, creating sparks.
The sparks caused violent pulses of electric current within the copper wires. These pulses reverberated within the wires, surging back and forth at a rate of roughly 100 million per second.
As Maxwell had predicted, the oscillating electric charges produced electromagnetic waves – radio waves – which spread out through the air around the wires. Some of the waves reached a loop of copper wire 1.5 meters away, producing surges of electric current within it. These surges caused sparks to jump across a spark-gap in the loop.
This was an experimental triumph. Hertz had produced and detected radio waves. He had passed electrical energy through the air from one device to another one located over a meter away. No connecting wires were needed.
Taking it Further
Over the next three years, in a series of brilliant experiments, Hertz fully verified Maxwell’s theory. He proved beyond doubt that his apparatus was producing electromagnetic waves, demonstrating that the energy radiating from his electrical oscillators could be reflected, refracted, produce interference patterns, and produce standing waves just like light.
Hertz’s experiment’s proved that radio waves and light waves were part of the same family, which today we call the electromagnetic spectrum.
Strangely, though, Hertz did not appreciate the monumental practical importance of the electromagnetic waves he had produced.
This was because Hertz was one of the purest of pure scientists. He was interested only in designing experiments to entice Nature to reveal its mysteries to him. Once he had achieved this, he would move on, leaving any practical applications for others to exploit.
The waves Hertz first generated in November 1886 quickly changed the world.
By 1896 Guglielmo Marconi had applied for a patent for wireless communications. By 1901 he had transmitted a wireless signal across the Atlantic Ocean from Britain to Canada.
Hertz’s discovery was the foundation stone for much of our modern communications technology. Radio, television, satellite communications, and mobile phones all rely on it. Even microwave ovens use electromagnetic waves: the waves penetrate the food, heating it quickly from the inside.
Our ability to detect radio waves has also transformed the science of astronomy. Radio astronomy has allowed us to ‘see’ features we can’t see in the visible part of the spectrum. And because lightning emits radio waves, we can even listen to lightning storms on Jupiter and Saturn.
Scientists and non-scientists alike owe a lot to Heinrich Hertz.
The Photoelectric Effect
In 1887, as part of his work on electromagnetism, Hertz reported a phenomenon that had enormous implications for the future of physics and our fundamental understanding of the universe. It came to be known as the photoelectric effect.
He shone ultraviolet light on electrically charged metal, observing that the UV light seemed to cause the metal to lose its charge faster than otherwise.
He wrote the work up, published it in Annalen der Physik, and left it for others to pursue. It would have been a fascinating phenomenon for Hertz himself to investigate, but he was too wound up in his Maxwell project at the time.
Experimenters rushed to investigate the new phenomenon Hertz had announced.
In 1899 J. J. Thomson, the electron’s discoverer, established that ultraviolet light actually ejected electrons from metal.
This led Albert Einstein to rethink the theory of light. In 1905 he correctly proposed that light came in distinct packets of energy called photons. Photons of ultraviolet light have the right amount of energy to interact with electrons in metals, giving the electrons enough energy to escape from the metal.
Einstein’s explanation of the photoelectric effect was one of the key drivers in constructing an entirely new way of describing atomic-scale events – quantum physics. Einstein was awarded the 1921 Nobel Prize in Physics for explaining the effect Hertz had discovered 34 years earlier.
Some Personal Details and the End
In 1886, aged 29, Hertz married Elisabeth Doll in Karlsruhe. She was the daughter of a mathematician. They had two daughters, Johanna and Mathilde. Mathilde became an influential biologist, making thought-provoking discoveries in the field of how animals solve problems.
At the age of 35 Hertz became very ill, suffering severe migraines. Doctors thought he had an infection. They performed a series of operations, but Hertz continued to deteriorate.
Heinrich Rudolf Hertz died aged 36 in Bonn on January 1, 1894 of blood-vessel inflammation resulting from immune system problems – specifically granulomatosis with polyangiitis. He was buried in his hometown of Hamburg, in the Ohlsdorf Cemetery.
In 1930 the unit of frequency was named the hertz by the International Electrotechnical Commission. In 1960 the unit was made official by the General Conference on Weights and Measures.
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