Heinrich Hertz, Scientist Who Proved Existence of Electromagnetic Waves

Heinrich Hertz
Heinrich Hertz (1857-1893), first exploited magnetic waves. His experiments led to the discovery of wireless telegraphy by Marconi.

Getty Images / Bettmann

Physics students around the world are familiar with the work of Heinrich Hertz, the German physicist who proved that electromagnetic waves definitely exist. His work in electrodynamics paved the way for many modern uses of light (also known as electromagnetic waves). The frequency unit that physicists use is named the Hertz in his honor.

Fast Facts Heinrich Hertz

  • Full Name: Heinrich Rudolf Hertz
  • Best Known For: Proof of the existence of electromagnetic waves, Hertz's principle of least curvature, and the photoelectric effect.
  • Born: February 22, 1857 in Hamburg, Germany
  • Died: January 1, 1894 in Bonn, Germany, at age 36
  • Parents: Gustav Ferdinand Hertz and Anna Elisabeth Pfefferkorn
  • Spouse: Elisabeth Doll, married 1886
  • Children: Johanna and Mathilde
  • Education: Physics and mechanical engineering, was a professor of physics in various institutes.
  • Significant Contributions: Proved that electromagnetic waves propagated various distances through the air, and summarized how objects of different materials affect each other on contact.

Early Life and Education

Heinrich Hertz was born in Hamburg, Germany, in 1857. His parents were Gustav Ferdinand Hertz (a lawyer) and Anna Elisabeth Pfefferkorn. Although his father was born Jewish, he converted to Christianity and the children were raised as Christians. This did not stop the Nazis from dishonoring Hertz after his death, due to the "taint" of Jewishness, but his reputation was restored after World War II.

The young Hertz was educated at the Gelehrtenschule des Johanneums in Hamburg, where he showed a deep interest in scientific subjects. He went on to study engineering in Frankfurt under such scientists as Gustav Kirchhoff and Hermann Helmholtz. Kirchhoff specialized in studies of radiation, spectroscopy, and electrical circuit theories. Helmholtz was a physicist who developed theories about vision, the perception of sound and light, and the fields of electrodynamics and thermodynamics. It is small wonder then, that the young Hertz became interested in some of the same theories and eventually did his life's work in the fields of contact mechanics and electromagnetism.

Life's Work and Discoveries

After earning a Ph.D. in 1880, Hertz took up a series of professorships where he taught physics and theoretical mechanics. He married Elisabeth Doll in 1886 and they had two daughters.

Hertz's doctoral dissertation focused on James Clerk Maxwell's theories of electromagnetism. Maxwell worked in mathematical physics until his death in 1879 and formulated what is now known as Maxwell's Equations. They describe, through mathematics, the functions of electricity and magnetism. He also predicted the existence of electromagnetic waves.

Hertz's work focused on that proof, which took him several years to achieve. He constructed a simple dipole antenna with a spark gap between the elements, and he managed to produce radio waves with it. Between 1879 and 1889, he did a series of experiments that used electrical and magnetic fields to produce waves that could be measured. He established that the velocity of the waves was the same as the speed of light, and studied the characteristics of the fields he generated, measuring their magnitude, polarization, and reflections. Ultimately, his work showed that light and other waves he measured were all a form of electromagnetic radiation that could be defined by Maxwell's equations. He proved through his work that electromagnetic waves can and do move through the air. 

In addition, Hertz focused on a concept called the photoelectric effect, which occurs when an object with electrical charge loses that charge very quickly when it is exposed to light, in his case, ultraviolet radiation. He observed and described the effect, but never explained why it happened. That was left to Albert Einstein, who published his own work on the effect. He suggested that light (electromagnetic radiation) consists of energy carried by electromagnetic waves in little packets called quanta. Hertz's studies and Einstein's later work eventually became the basis for an important branch of physics called quantum mechanics. Hertz and his student Phillip Lenard also worked with cathode rays, which are produced inside vacuum tubes by electrodes. 

Heinrich Hertz
Heinrich Hertz's portrait and drawings of electrical fields that he studied appeared on a German postage stamp in 1994. Deutsche Bundespost.

What Hertz Missed

Interestingly, Heinrich Hertz did not think his experiments with electromagnetic radiation, particularly radio waves, had any practical value. His attention was focused solely on theoretical experiments. So, he proved that electromagnetic waves propagated through the air (and space). His work led others to experiment even further with other aspects of radio waves and electromagnetic propagation. Eventually, they stumbled across the concept of using radio waves to send signals and messages, and other inventors used them to create telegraphy, radio broadcasting, and eventually television. Without Hertz's work, however, today's use of radio, TV, satellite broadcasts, and cellular technology wouldn't exist. Nor would the science of radio astronomy, which relies heavily on his work. 

Other Scientific Interests

Hertz's scientific accomplishments weren't limited to electromagnetism. He also did a great deal of research on the topic of contact mechanics, which is the study of solid matter objects that touch each other. The big questions in this area of study have to do with the stresses the objects produce on each other, and what role friction plays in interactions between their surfaces. This is an important field of study in mechanical engineering. Contact mechanics affect design and construction in such objects as combustion engines, gaskets, metalworks, and also objects that have electrical contact with each other. 

Hertz's work in contact mechanics began in 1882 when he published a paper titled "On the Contact of Elastic Solids," where he was actually working with the properties of stacked lenses. He wanted to understand how their optical properties would be affected. The concept of "Hertzian stress" is named for him and describes the pinpoint stresses that objects undergo as they contact each other, particularly in curved objects. 

Later Life

Heinrich Hertz worked on his research and lecturing until his death on January 1, 1894. His health began failing several years prior to his death, and there was some evidence he had cancer. His final years were taken up with teaching, further research, and several operations for his condition. His final publication, a book titled "Die Prinzipien der Mechanik" (The Principles of Mechanics), was sent to the printer a few weeks before his death. 

Honors

Hertz was honored not only by the use of his name for the fundamental period of a wavelength, but his name appears on a memorial medal and a crater on the Moon. An institute called the Heinrich-Hertz Institute for Oscillation Research was founded in 1928, known today as the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI. The scientific tradition continued with various members of his family, including his daughter Mathilde, who became a famous biologist. A nephew, Gustav Ludwig Hertz, won a Nobel prize, and other family members made significant scientific contributions in medicine and physics. 

Bibliography

  • “Heinrich Hertz and Electromagnetic Radiation.” AAAS - The World's Largest General Scientific Society, www.aaas.org/heinrich-hertz-and-electromagnetic-radiation. www.aaas.org/heinrich-hertz-and-electromagnetic-radiation.
  • Molecular Expressions Microscopy Primer: Specialized Microscopy Techniques - Fluorescence Digital Image Gallery - Normal African Green Monkey Kidney Epithelial Cells (Vero), micro.magnet.fsu.edu/optics/timeline/people/hertz.html.
  • http://www-history.mcs.st-and.ac.uk/Biographies/Hertz_Heinrich.html“Heinrich Rudolf Hertz.” Cardan Biography, www-history.mcs.st-and.ac.uk/Biographies/Hertz_Heinrich.html.