By Jacqueline Hochheiser, Corporate Communications
Experimental physicist Heinrich Hertz played an instrumental role in the development of wireless communication, although he didn’t believe that his discovery had any practical use at the time. Hertz became an influential figure in the physics community when he produced concrete evidence of the existence of electromagnetic waves, or “invisible waves,” as he referred to them in his 1887 paper titled “On Electromagnetic Effects Produced by Electrical Disturbances in Insulators.” In honor of his discovery, the unit used to measure the frequency of EM waves was called Hertz (Hz).
Heinrich Hertz was born in Hamburg, Germany on February 22, 1857 to Gustav Ferdinand Hertz and Anna Elisabeth Pfefferkorn. Hertz’s parents belonged to the Hanseatic family of the German social elite, so education was of high importance when Hertz was growing up.
By the young age of six, Hertz had already expressed an interest in math and science. Hertz’s mother was particularly attentive to his studies and enrolled him in the Dr. Wichard Lange School for boys, founded and directed by the esteemed German scientist Friedrich Wichard Lange. The curriculum was unconventional in that it did not include classical teachings of religion, Greek and Latin, but was instead entirely focused in math and science.
Seeing her son’s progress and aptitude for learning, Hertz’s mother enrolled him in additional lessons at a local technical college on Sundays. At age 15, Hertz left the Lange School to undergo private tutoring at his family home to prepare him for University. In addition to his math and science lessons, Hertz now had a tutor in Greek and Latin to ensure he was ready for the university’s compulsory entry exams in classical studies. During this time, Hertz began to conduct experiments at home by building scientific apparatuses like the spectroscope.
A Rising Prodigy
By age 17, Hertz returned to school for a year at the Johanneum Institute in Lubeck, Germany to continue studying for his classical exams. In 1876, the extra work proved successful when Hertz moved to Dresden to attend the University of Munich in pursuit of an engineering career. He took classes in math, experimental physics and experimental chemistry. It wasn’t until he decided to earn a Ph. D in 1878 that Hertz’s reputation began to flourish within the scientific community.
Hertz attended the University of Berlin at the age of 21 in pursuit of his Ph. D. He studied under the accomplished German physicist Hermann von Helmholtz, who made many contributions to fields such as physiology, psychology, physics and philosophy. Helmholtz introduced Hertz to the theory of Scottish physicist James Clerk Maxwell, who predicted that electric and magnetic fields travel through space as waves.
Maxwell’s theory, published in 1864, was based upon equations he derived from other great scientists including Michael Faraday, William Thomson and Carl Friedrich Gauss. Maxwell believed that light inhabited the same medium responsible for electric and magnetic phenomena in the form of invisible waves. Although Maxwell’s equations made a good argument, they did not supply any concrete proof.
Helmholtz proposed that the Prussian Academy of Sciences, which was responsible for the Berlin Prize for scientific achievements, should give the prize to the scientist who was able to prove Maxwell’s theory of invisible waves, feeling that Hertz would be the one to do it.
Helmholtz encouraged Hertz to take on the challenge and to write his doctoral thesis on the subject. Surprisingly, Hertz turned down the opportunity, claiming it would take many years to solve considering he didn’t know how to build an apparatus to test the theory. He was in a hurry to create a name for himself in the field and opted for something timelier. His doctoral thesis, published when he was 23 years old, was ultimately written on electromagnetic induction.
Revealing Invisible Waves
Unable to resist the temptation of a difficult problem, Hertz continued to study Maxwell’s theory after he finished his doctoral education. He became an assistant professor to Helmholtz at the University of Berlin, but eventually became a full professor of theoretical physics at the University of Kiel in 1883. He soon found that the theoretical nature of his practice at Kiel didn’t suit his tendency toward experimental physics, so he made the decision to move to Karlsruhe Polytechnic University in 1885, where he had access to state-of-the-art laboratories.
While teaching his students about sparks using an instrument called a Riess spiral, Hertz’s interest was piqued. A Riess spiral consists of two coils of conductor wire that form an induction coil. The conductor wires have hollow metal balls at their ends and sparks jump between the balls when an electric current is sent through the device.
Hertz knew that sparks, composed of both electricity and light, are made up of rapidly accelerating and decelerating electric charges, resulting in regular vibrations within the conductor wires they jump between. Based upon this phenomenon, if Maxwell’s theory was correct, the vibrations caused by the sparks would radiate electromagnetic waves that pass through the air.
It was the Riess spiral that inspired Hertz’s first apparatus, a crude oscillator, used to test Maxwell’s theory. He attached an induction coil to two, one meter long copper conductor wires separated by a 7.5 mm spark gap. On the opposite end of both wires was a hollow zinc ball, 30 cm in diameter.
Hertz then used a Leyden Jar attached to the induction coil to send high voltage electric pulses down the conductor wires resulting in a spark jumping across the gap. The spark produced vibrations that traveled quickly back and forth across the wires. These vibrations were supposedly the source of emanating electromagnetic waves.
To find the waves, Hertz also constructed a rudimentary antenna made from 1mm thick brass wire formed into a loop with a 7.5 cm diameter. The loop had its own spark gap and was set approximately 1.5 meters from the oscillator.
Hertz varied the position of the antenna each time he sent electric pulses through the oscillator until, finally, sparks jumped across the antenna’s spark gap. The vibrations caused by the sparks in the oscillator were indeed emanating electromagnetic waves, which Hertz was able to pick up with his antenna by show of what he called side sparks. The side sparks were proof that his antenna was receiving electromagnetic waves travelling through the air as Maxwell had predicted.
Confirming Maxwell’s Theory
Over the next three years, Hertz continued to experiment and verify other aspects of Maxwell’s theory. He not only proved that electromagnetic waves existed with his antenna and oscillator, but he also proved that this radiation could be reflected, refracted and that it could produce interference patterns and standing waves just as light could.
In this way, Hertz validated Maxwell’s prediction that radio waves and light not only acted in a similar manner, but were part of the same family of energy; the electromagnetic spectrum. He was able to determine the waves’ speed and velocity by first finding its wavelength.
To do this, Hertz reflected the radiated waves with a mirror to create a standing wave. Within the standing wave are nodes, or points along the wave that are static. The reflection of the waves also caused interference with the production of antinodes, the points of greatest fluctuation along the wave. Hertz could determine where the nodes and antinodes of a wave were depending on if a spark occurred on the antenna’s spark gap.
The length from one node to an antinode to another node equals one wavelength. Hertz could find a node by detecting a spot that did not produce a spark on his antenna. He would then move the antenna backward until he found a spark, and move back even further until there was no spark. After gauging the wavelength, Hertz was then able to calculate frequency and concluded that the waves were traveling at the speed of light, just as Maxwell’s theory suggested.
Ironically, Hertz’s pursuit of the discovery of radio waves was motivated solely by his interest in uncovering natural phenomena. He never imaged that radio waves would have any practical purpose. He was only interested in finding merit in Maxwell’s theory because he enjoyed exposing natural mysteries that physics and mathematics helped to solve.
After proving Maxwell’s theory, Hertz published his findings in a thesis titled, “On Electromagnetic Effects Produced by Electrical Disturbances in Insulators.” His work elevated him as a prominent figure in the physics and mathematics community. In 1889, he took a position at the Physics Institute in Bonn as the director of the institute and professor of physics.
Unfortunately, this would be his last position before his death on January 1, 1894. At only 36 years old, Hertz died from blood vessel inflammation resulting from an immune disorder. He left behind his wife Elisabeth Doll and their two daughters Johanna and Mathilde, the latter of whom would become a noted biologist. Hertz was buried at his hometown of Hamburg in the Ohlsdorf Cemetery.
Despite his untimely death, Hertz’s discoveries made a profound, lasting contribution to our understanding of electromagnetism and laid the foundation for wireless communication and the advent of a new industry. Guglielmo Marconi would soon envision the potential for the use of radio waves as a form of communication, which would change the world in ways that would’ve been unimaginable without Hertz’s discoveries.