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ArrowHeinrich Hertz (1857-1894)

Heinrich Hertz

German physicist Heinrich Hertz discovered radio waves, a milestone widely seen as confirmation of James Clerk Maxwell’s electromagnetic theory and which paved the way for numerous advances in communication technology. Born in Hamburg on February 22, 1857, Hertz was the eldest of five children. His mother was Elizabeth Pfefferkorn Hertz and his father was Gustav Hertz, a respected lawyer who would later become a legislator. In his youth Heinrich displayed an interest in building things, and as a teenager he constructed a spectroscope and a galvanometer that were so well designed that Hertz used them throughout his college years. Initially Hertz planned a career in engineering, but after a year of employment at the public works office in Frankfurt, a summer of classes at the Polytechnic in Dresden, a year of military service in Berlin, and a brief stint in the engineering department at the University of Munich, he finally decided to pursue the subject that most deeply interested him: science.

Throughout his life Hertz read works on science and carried out experiments as a hobby. But once he decided that science was to be his career, he applied himself to these tasks with even greater enthusiasm. In the winter of 1877, he studied various scientific treatises, and the following spring, he gained some laboratory experience by working with Gustav von Jolly. Subsequently he enrolled at the University of Berlin, where he was privileged to study under the great German physicist Hermann von Helmholtz. With Helmholtz’s encouragement, Hertz resolved to compete for a research prize to be awarded to the student best able to determine whether or not electricity moved with inertia. Hertz began a series of experiments into the matter, and this mode of learning seemed to suit him. He confided in a letter sent to his family during that time, "I cannot tell you how much more satisfaction it gives me to gain knowledge for myself and for others directly from nature, rather than merely learning from others and for myself alone."

In August of 1879, Hertz won the prize for his evidence demonstrating that electricity had no inertia. Another prize problem was soon proposed by Helmholtz, who wanted students to attempt to prove which of the theories of electromagnetic phenomena then circulating was correct. Interestingly, Hertz did not choose to compete for this prize, but years later would be the first person to successfully provide the kind of definitive evidence that Helmholtz sought. At the time, Hertz instead embarked on a study of induction produced by rotating spheres. His work in this area helped him earn his doctorate degree ahead of schedule, in 1880, magna cum laude.

Hertz’s first academic post was as lecturer of theoretical physics at the University of Kiel, but due to his dissatisfaction there he accepted a position at the Karlsruhe Polytechnic in 1885. It was at Karlsruhe, where he remained until he received an appointment as physics professor at the University of Bonn in 1889, that Hertz carried out his most important work. In 1886, Hertz began experimenting with sparks emitted across a gap in a short metal loop attached to an induction coil. He soon built a similar apparatus, but without the induction coil, to act as a detector. When the induction coil connected to the first loop (the transmitter) produced a high voltage discharge, a spark jumped across the gap, sending out a signal that Hertz detected as a weaker spark across the gap in the receiving apparatus, which he placed nearby. To determine the nature of the signals that he was able to transmit and receive, Hertz developed a number of innovative experiments.

By measuring side sparks that formed around the primary spark and varying the position of the detector, Hertz was able to determine that the signal exhibited a wave pattern, and to ascertain its wavelength. Then, by using a rotating mirror, he found the frequency of the invisible waves, which enabled him to calculate their velocity. Amazingly, the waves were moving at the speed of light. Thus, it appeared to Hertz that he had discovered a previously unknown form of electromagnetic radiation, and in the process confirmed James Clerk Maxwell’s theory of electromagnetism. To further prove that this was indeed the case, Hertz continued his experiments exploring the behavior of the invisible waves. He discovered that they traveled in straight lines and could be focused, diffracted, refracted and polarized. Hertz announced his initial discovery in late 1887 in his treatise "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators”, which he sent to the Berlin Academy. He later published additional details following the series of experiments he carried out in 1888. For a time the waves he discovered were commonly referred to as Hertzian waves, but today they are known as radio waves.

In addition to his radio wave breakthrough, Hertz is notable for the discovery of the photoelectric effect, which occurred while he was investigating electromagnetic waves. Because of some difficulty in detecting the small spark produced in his receiving apparatus, Hertz sometimes placed the receiver in a dark case. This, he found, affected the maximum length of the spark, which was smaller than when he did not use the case. With further research into the phenomenon, Hertz discovered that the spark produced was stronger if it was exposed to ultraviolet light. Though he did not attempt to explain this fact, others, including J.J. Thomson and Albert Einstein, would soon realize its importance. The phenomenon of electrons being released from a material when it absorbs radiant energy, which was the cause of the stronger sparks observed by Hertz when ultraviolet radiation was used, would come to be known as the photoelectric effect.

After 1889, when Hertz was teaching at the University of Bonn, he studied electrical discharges in rarefied gases and spent a significant amount of time composing his Principles of Mechanics. Unfortunately, he never saw the work published due to his premature death associated with blood poisoning on New Year’s Day 1894. Only 37 years old at the time, Hertz also never lived to see the tremendous impact the discovery of radio waves would have on the world in the 20th century.


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