Heinrich Rudolf Hertz was the first to broadcast and receive radio waves in the laboratory. Between 1885 and 1889, he used spark discharges to produce electromagnetic waves. Heinrich Rudolf Hertz was born on 22 February, 1857, in Hamburg. His father Dr. jur. Gustav Ferdinand Hertz was Jewish, who had converted to Christianity.
He was an advocate in Hamburg, then Oberlandsgerichtsrat, and from 1887 Senator and head of the administration of justice. His mother Anna Elisabeth, nee Pfefferkorn, was the daughter of the Frankfurt doctor, Dr. Pfefferkorn.
After attending a private Realschule, Heinrich prepared himself, by private study, for the Johanneum school at which in 1875, after only a year of studying, he passed his school-leaving and university entrance exam Abitur (GCE A-levels), the best in his class. He showed an early interest in the natural sciences, and a practical skill in building physics equipment in the family workshop. He was also an enthusiastic linguist, learning Arabic and Sanskrit.
Then Heinrich Hertz went to Frankfurt to gain practical experience in engineering and after a year of military service with a railway regiment in Berlin (1876-77) he spent a year at the University of Munich.
He had decided on an academic and scientific career rather than one in engineering, and in 1878 chose to continue his studies at the University of Berlin under Gustav Kirchhoff and Hermann von Helmholtz, the foremost physicists of the time. Hertz obtained his Ph.D. degree magna cum laude in 1880 with a thesis on the electromagnetic induction in rotating spheres and continued as Helmholtz’s assistant for a further three years.
In 1883 Hertz became a lecturer in theoretical physics at the University of Kiel. With no laboratory facilities at Kiel he had considered more theoretical aspects of physics. Here he began his studies of the recent electromagnetic theory of James Clerk Maxwell.
Maxwell’s theory had been based on unusual mechanical ideas about the luminiferous ether and had not been universally accepted. Another scientist, Michelson, assisted by Morley, performed a remarkably clever experiment that proved the non-existence of this ether. In 1884, Hertz rederived Maxwell’s equations by a new method, casting them in modern form without assumption of ether.
Heinrich Hertz, a young scientist
In 1885, at the age of 28, Heinrich Hertz was appointed professor of physics at the Karlsruhe University. Hertz’s early work in Karlsruhe was diverse but included several pieces of research into electrical phenomena and equipment. Helmholtz had suggested an experimental investigation of the theory to Hertz in 1879, but it was not until 1885 in Karlsruhe that Hertz found the equipment needed for what became his most famous experiments.
Karlsruhe University where Hertz was working from 1885 to 1888
In 1886 Hertz married Elizabeth Doll, daughter of a Karlsruhe professor; they had two daughters (Johanna, born on 20.10.1887 and Mathilde, born on 14.01.1891).
It is interesting to note that in 1887 he inadvertently discovered the photoelectric effect whereby ultraviolet radiation releases electrons from the surface of a metal. Although realizing its significance he left others to investigate and explain it.
In 1888, in a corner of his physics classroom at the Karlsruhe Polytechnic in Berlin, Hertz generated electric waves using an electric circuit; the circuit contained a metal rod that had a small gap at its midpoint, and when sparks crossed this gap violent oscillations of high frequency were set up in the rod.
Hertz proved that these waves were transmitted through air by detecting them with another similar circuit some distance away. He also showed that like light waves they were reflected and refracted and, most important, that they traveled at the same speed as light but had a much longer wavelength.
Hertz also noted that electrical conductors reflect the waves and that they can be focused by concave reflectors. He found that nonconductors allow most of the waves to pass through. These waves, originally called Hertzian waves but now known as radio waves, conclusively confirmed Maxwell’s prediction on the existence of electromagnetic waves, both in the form of light and radio waves.
Hertz in his lab, doing experiments with electromagnetic waves
Hertz’s first radiator
In his experiments, Hertz first employed a pair of one meter wires with a spark gap in the center connected to an induction coil as a radiator. The large spheres at the ends were used to adjust the capacity of the circuit for resonance. His receiver was a loop of wire with a small gap across which a small spark could be observed when the radiator discharged.
The receiver was placed several yards from the oscillator. When these rods were given charges of opposite signs, strong enough to spark, the current would oscillate back and forth across the gap and along the rods. With this oscillator, Hertz solved two problems: 1) timing Maxwell’s waves (he had demonstrated, in the concrete, what Maxwell had only theorized: that the velocity of radio waves was equal to the velocity of light), and 2) how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell’s waves.
Hertz’s students were impressed, and wondered what use might be made of this marvelous phenomenon. But Hertz thought his discoveries were no more practical than Maxwell’s. “It’s of no use whatsoever,” he replied. “This is just an experiment that proves Maestro Maxwell was right – we just have these mysterious electromagnetic waves that we cannot see with the naked eye.
But they are there.” “So, what next?” asked one of his students. Hertz shrugged. He was a modest man, of no pretensions and, apparently, little ambition. “Nothing, I guess.” But, even at a theoretical level, Hertz’s accomplishments were quickly seen by others as the beginning of a new “electric age.” The English mathematical physicist, Sir. Oliver Heaviside, said in 1891, “Three years ago, electromagnetic waves were nowhere. Shortly afterward, they were everywhere.”
Summing up Hertz’ experiment importance: his experiments dealing with the reflection, refraction, polarization, interference and velocity of electric waves would trigger the invention, soon after, of the wireless telegraph, radio, television, and radar.
It happened this way: in 1888, Hertz described in an electrical journal how he was able to trigger his electromagnetic waves with his oscillator. A young man in his teens happened to read the article while he was vacationing in the Alps. For him, Hertz’s discovery gave him an idea: why not use the waves set off by Hertz’s spark oscillator for signaling? Guglielmo Marconi was that young man. He rushed back home to Italy to give the idea a try.
Photograph of Heinrich Hertz, probably taken about 1888-89 when he had just completed his ground-breaking work on electromagnetic waves in Karlsruhe.
Heinrich Hertz, probably just a few months before he moved to Bonn as Professor of Physics in April, 1889. This photograph was taken in his Karlsruhe Laboratory.
On April 3, 1889, Heinrich Hertz arrived in Bonn to take the position of Professor of Physics and Director of the Physics Institute as successor to Rudolf Clausius (1822-1888). Hertz was fresh from his triumphs in Karlsruhe, where he had proved in a series of elegant experiments that the long-wavelength electromagnetic waves implicit in Maxwell’s theory existed.
He also had been able to demonstrate convincingly that these waves had all the well-known properties of light waves – reflection, refraction, interference, polarization.
Almost immediately Hertz became the superstar of the physics community, not merely in Germany but throughout the world of science. But during the almost five years that Hertz spent in Bonn (April 3, 1889, to January 1, 1894), he abandoned almost all experimental work and devoted three years to difficult theoretical work on mechanics, which culminated in the posthumous publication in 1894 of his book on the subject.
(Heinrich Hertz, Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt, Philipp Lenard (Ed.), Leipzig: J.A. Barth, 1894; translated by D.E. Jones, J. T. Walley, The Principles of Mechanics Presented in a New Form, London: Macmillan and Co., 1899; reprinted New York: Dover Publications, 1956.)
Why, in his hour of triumph, did Hertz turn his back on electromagnetic experiments (after completing one that he had begun in Karlsruhe), and devote three years to this book on mechanics, a book that always has mystified physicists? A practical reason (but certainly not the dominant one) is that he was increasingly ill with a series of infections during these years, and thus was unable to do the laboratory research he found so rewarding both personally and professionally.
He also found it difficult to find new experimental projects that promised to rival his Karlsruhe research in importance. The salient reason for his work on theoretical mechanics, however, was that as a nineteenth-century physicist, like most such physicists, Hertz firmly maintained that the ultimate goal of physics was to reduce all observable physical phenomena to mechanics.
In addition to his theoretical studies in mechancs, Hertz performed research on the discharge of electricity in rarefied gases. Hertz also continued his analysis of Maxwell’s theory, publishing two papers in 1890. His experimental and theoretical work put the field of electrodynamics on a much firmer footing. His scientific papers were translated into English and published in three volumes: Electric Waves (1893), Miscellaneous Papers (1896), and Principles of Mechanics (1899).
Physical Institute of the Bonn University where Heinrich Hertz worked and lived from 1889 till his death in 1894.
Hertz suffered from a bone disease during Summer 1892. Heinrich Hertz died of blood poisoning on 1 January 1894 in Bonn, when not quite 37. His tragic early death occurred after several years of poor health and cut short a brilliant career. He is buried in the Jewish cemetery in Ohlsdorf, Hamburg, Germany. Photographs of Heinrich Hertz’s gravestone in the cemetery of Hamburg-Ohlsdorf, Germany.
When Hertz died, Sir Oliver Lodge gave Hertz credit for accomplishing that the great English physicists of the time were unable to do. It was not hard to give Hertz credit: “Not only had he established the validity of Maxwell’s theorems, he had done so with a winning modesty.
“He was a noble man,” said one eulogist in 1894, “who had the singular good fortune to find many admirers, but none to hate or envy him; those who came into personal contact with him were struck by his modesty and charmed by his amiability. He was a true friend to his friends, a respected teacher to his students, who had begun to gather around him in large numbers, some of the coming from great distances; and to his family a loving husband and father.”
The importance of Heinrich Hertz’s research for the development of physics in the early twentieth century was well summarized in a letter of Ludwig Boltzmann to Hermann von Helmholtz on January 6, 1894, just a few days after Hertz’s death: “One should emphasize the extraordinary import of Hertz’s discoveries in relation to our whole concept of Nature, and the fact that beyond a doubt they have pointed out the only true direction that investigation can take for many years to come.”
In recognition of Hertz’ work, his name is now given to the unit of frequency – one cycle per second – (Hertz) and is abbreviated Hz. This replaced the use of cycles per second for the unit of frequency in the late 1960′s.
In 1899, only five years after his death, Hamburg honoured Heinrich Hertz by naming a street in the district of Uhlenhorst after him: Heinrich-Hertz-Stra’e, 22083/22085 Hamburg. A primary school is named after him: Heinrich-Hertz-Grundschule, Po’moorweg 22, 22301 Hamburg, and a Gesamtschule (comprehensive school): Heinrich-Hertz-Schule, Grasweg 72-76, 22303 Hamburg.
A portrait of Heinrich Hertz is one of the 56 portraits, in relief, of eminent citizens of Hamburg, on the columns in the entrance hall of the Rathaus (Town Hall). His was one of the six out of seven “Jewish” portraits removed by the Nazis. This action took place without it being reported in the press. In 1949, the portraits were replaced.
After the Second World War, Hamburg named the circa 270 metre TV Tower in Rentzelstra’e after him, Heinrich-Hertz-Turm. A plaque, on the tower, approximately 20 metres above the ground, carries the inscription: Heinrich Hertz dem Sohn der Stadt Hamburg.
The postal stamps in recognition of Hertz’ scientific achievements
The IEEE Heinrich Hertz Medal was established by the Board of Directors in 1987 “for outstanding achievements in Hertzian (radio) waves.” It may be presented annually to an individual for achievements which are theoretical or experimental in nature.” The medal is named in honor of the renowned scientist whose experiments verified Maxwell’s theory and proved that all forms of electromagnetic radiation are propagated as waves at a finite velocity – the speed of light.
Heinrich Hertz memorial medal made in the East Germany, 1969
Since 1923 and the collapse of German currency, the Hertz’ widow Elizabetth with two daughters, Johanna and Mathilde, had survived on the charity of radio companies in various lands. Heinrich’s half-Jewish parentage (through his grandfather, a convert to Lutheranism) led in the Nazi Germany of 1935 to Mathilde’s being dismissed from her university teaching post.
With the help of Max von Laue and Erwin Schrodinger she found temporary refuge in Oxford, but it was J.J. Thomson in Cambridge (who had met and been impressed by Heinrich in 1890) who helped her settle in a village Girton (three miles from the center of Cambridge, England); in 1937 Mathilde persuaded her mother and sister to join her. The three women had little to live on beyond one-off gifts from the Pope and from the Institution of Electrical Engineers. Elizabetth Hertz survived her husband by almost 48 years. She died in the age of 77 on December 28, 1941, in Girton.
Heirnrich Hertz’ nephew Gustav Ludwig Hertz was a 1925 Nobel Prize winner in Physics (together with James Franck) “for their discovery of the laws governing the impact of an electron upon an atom” and Gustav’s son Carl Hellmuth Hertz invented medical ultrasonography and ink jet printing.