Biography On: Heinrich Rudolf Hertz (1857-94)

by Brian W. Miller

Associated with the University of Arizona Optical Sciences Center

molinero@email.arizona.edu

Abstract

At the end of the 19^th century, many important scientific discoveries where occurring. The theory of the existence of electromagnetic radiation had been hypothesized by James Clerk Maxwell, but it was Heinrich Rudolf Hertz who was the first to verify it. In 1887 Heinrich Hertz transmitted and received the first radio waves. His contribution and discovery brought about the advent of radio and television communication.

Biography

Heinrich Rudolph (Rudolf) Hertz was born Feb. 22, 1857 in Hamburg, Germany. The 1850’s was a period of sustained economic expansion and political retrenchment in Germany [1]. Heinrich’s father, Gustav Hertz, was a prominent lawyer and his mother Anna Elisabeth was the daughter of a Frankfurt physician. Though Gustav was of Jewish descent and raised a Lutheran “neither he nor Anna Elisabeth were concerned to raise their child in a religious atmosphere [1].” The family focused on the children’s intellectual and moral character and it is evident that Heins’ father had great influence on his development. Anna reflects, “At meals, the only time during the week when my husband saw the children, it was their interests that occupied us and our intimate chats made the hour dear to us [1].”

At an early age Heinrich demonstrated an eager desire to learn. His mother describes the shaping of Hein’s during the ages fifteen through seventeen: “When he sat with his books nothing could disturb him nor draw him away from them. His desk stood in a room through which I often had to pass, but I always saw him bent over his books in the same way, deep in his work. We never exchanged a word. At 12:30 we both had lunch with our little Otto [his youngest brother]. Half an hour’s play with the little boy was his only relaxation. Then he studied afresh, mostly until dinner time at 5 o’clock [1].”

As Hertz continued his education, it is evident that he went through a process of discovering where his true interests lay. Heinrich studied engineering mathematics at the Polytechic at Dresden from 1875-1876, military at Imperial Berlin from 1876-1877, and finally physics at the Polytechnic in Munich [1]. In Dresden, Heinrich discovered a captivation for mathematics and described it as “sometimes marvelous things come in view that makes one’s head swim [1].” Buchwald informs us that within a month he had decided that engineering was not for him and he decided to enroll at the university. The change in major required the permission of his parents and he expresses his desire in a letter to them:

“I cannot understand why I didn’t not realize it before now, for even in coming here it was with the best intention of studying mathematics and the natural sciences and with not thought at all about surveying, building construction, builders’ materials, etc., which were supposed to be my main subject. I would rather be an important scientist than an important engineer, but rather an unimportant engineer than an unimportant scientist; yet now, as I stand on the brink, I think that what Schiller said is also true: ‘And if you don’t dare to stake your life, you can never hope to with the strife,’ and that too much caution would be folly [1].” Heinrich was willing “stake” his life in the pursuit of physics

It is readily seen that Heinrich Hertz was fascinated with the sciences and his zeal to understand would lead him to one of the most important discovers of the 19^th century.

Heinrich continued his studies at the University of Berlin and received his Doctor of Philosophy degree magna cum laude. During this time Heinrich was an assistant to Hermann von Helmholtz [2]. Helmholtz had done work in mathematical physics and acoustics and was interested in musical theory and the perception of sound [3]. In 1883 Hertz became a lecturer in theoretical physics at the University of Kiel and was later appointed professor of physics at Karlsruhe Polytechic [2]. Shortly thereafter in 1886, Heinrich married Elizabeth Doll became the father of two daughters.

Looking at the contemporary events of Heinrich’s day, Europe was experiencing a period of relative peace. Some of the worlds brightest minds, Helmholtz and Maxwell for instance, had contributed remarkable work on the theory of electromagnetics. A race existed among theorists, scientists, and engineers to verify the Maxwellian theory and the potential applications thereof.

Hertz’s Experiment

A predicted theory of James Clerk Maxwell (1831 - 1879), a Scottish scientist, had been established that could be used to explain electricity and magnetism phenomena. Included in Maxwell’s theory was the coupling of electricity and magnetism shown by the equations in Figure 2. Equations 1 and 2 describe the interactions between an electric and magnetic field. A changing magnetic field will induce an electric field and vice versa. Equation 3 shows that magnetic monopoles do not exists, i.e., whenever you have a magnetic field there always exists a coupled north and south pole. Equation 4 describes the relation of charge density and the electric field.

[7]

Maxwell’s Equations

1.
2.
3.
4.

Figure 2 [5]

It was also theorized that an electromagnetic wave could be generated that could transmit through space. In Figure 1 we see a coupled magnetic and electric field. The changing magnetic field will generate the electric field and vice versa. This phenomena is known as electromagnet radiation, i.e., light (radio waves, microwaves, optical waves, ultraviolet waves, x-rays, etc.). In the 1880’s physicists were trying to obtain experimental evidence of Maxwell’s hypotheses electromagnetic waves, and it was in 1887 when Hertz was the first to experimentally produce them [2].

Figure 3 Oscillator used to produce electromagnetic waves. [6]

Figure 4 Receiver loop wire[6]

Hertz used an oscillator made of polished brass knobs (see figure 3) so that when a high enough voltage was applied, sparks could leap across the small air gap [2]. If Maxwell’s theory was correct, every time a spark occurred, an electromagnetic wave would be generated. To prove this theory he took a loop of wire with two polished brass knobs, separated by a small gap (see figure 4). This receiver was placed several yards from the oscillator [2]. When the oscillator was turned on, it transmitted electromagnetic waves which spread outward from the sparks. These waves induced a current in the receiver loop, which in turn produced a spark [2]. Heinrich Hertz became the first to experimentally transmit and receive electromagnetic waves.

The electromagnetic waves that Hertz produced would have been in the frequency range of radio waves. The frequency is determined by dividing the speed of light (300,000,000 meters/second) by the wavelength of the electromagnetic wave (υ = c/λ). For radio waves, the wavelength is very long compared to the wavelength of visible light (meters compared to nanometers). Radio wave wavelengths can range from centimeters to meters in length. For example, using the formula υ = c/λ with a wavelength of 1 meter, this would correspond to a frequency 300,000,000 cycles per second.

In addition to the generation of electromagnetic waves, Hertz showed that conductive materials reflect the waves and non conductors allow them to pass through, and also that they can be focused by concave reflectors.

Conclusion

Heinrich Rudolf Hertz’s contributions and discoveries to science are far reaching and we benefit from them in our everyday lives. He experimentally verified James Clerk Maxwell’s hypothesis and was the first person to produce radio waves. Hertz also contributed to knowledge about electromagnetic waves and their corresponding properties. With his discovery came the advent of radio, television, and communication technology which ushered in a new world of communication. In 1894 at Bonn, Germany, Hertz died of blood poisoning at the age of 36 [4].

At his eulogy, one said "He was a noble man 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 [2]."

In honor of this great scientist of the 19^th century, the unit Hertz (cycle or wave per second), was named after him.

Bibliography

1. Buchwald, Z. (1994). The Creation of Scientific Effects – Heinrich Hertz and Electric Wave. USA: The University of Chicago Press Chicago and London.
2. Naughton, R. (2003). “Adventures in Cybersounds: Heinrich Rudolphs (alt:Rudolf) Hertz, Dr: 1857 – 1894”. http://www.acmi.net.au/AIC/HERTZ_BIO.html
3. Web (2003). “Hermann Ludwig Ferdinand von Helmholtz (1821 - 1894)”. http://gifted.kaist.ac.kr:7777/html/internet/echide/science/www.kcsnet.or.kr/education/fame/Helmholtz.html
4. Nelson, I. (2003), “Maxwell’s equations.” http://www.slcc.edu/schools/hum_sci/physics/tutor/2220/maxwells/
5. Maxwell’s Equations: http://en.wikipedia.org/wiki/Maxwell's_equations
6. Experiment Figures: http://www.sparkmuseum.com/BOOK_HERTZ.HTM
7. E/M figure http://micro.magnet.fsu.edu/primer/java/electromagnetic/