Heinrich Rudolf Hertz (The German physicist)

Heinrich Rudolf Hertz

The German physicist Heinrich Rudolf Hertz (1857-1894) demonstrated experimentally the propagation of electrical oscillations in space.

Born on February 22, 1857, in Hamburg, Heinrich Hertz was the oldest of the five children of Gustav Hertz, a lawyer and later a senator and the head of the judiciary of the city of Hamburg, and Elizabeth Pfefferkorn Hertz. Heins, as the boy was called in the family, soon gave evidence of his extraordinary aptitudes in mathematics, science, languages, and manual skills. The galvanometer and the spectroscope which he constructed as a teen-ager served him well during his university studies.

In addition to a thorough acquaintance with Homer and the Greek dramatists, Hertz acquired through his own efforts a knowledge of Sanskrit and Arabic. Following his graduation with highest honors from the gymnasium in Hamburg in 1875, he thought that his future lay with engineering. He spent a year in Frankfurt with an engineering firm, and in the summer of 1876 he attended courses at the Polytechnic in Dresden. After a year of volunteer military service in Berlin he began his regular engineering studies at the University of Munich in 1877.

No sooner had the classes gotten under way than it dawned on Hertz that he would prefer physics to engineering. He spent the winter of 1877/1878 studying the treatises of Pierre Simon de Laplace and Joseph Louis Lagrange and the spring in the laboratory working under G. von Jolly. To achieve the best training, he sought out the best teachers, and these were at the University of Berlin. Soon after his arrival there he became Hermann von Helmholtz's student. By spring 1879 Hertz completed the experimental verification of a question about electrical inertia, and his work won a gold medal at the university on August 4.

Demonstration of Electromagnetic Oscillations

Hertz's combination of theoretical and experimental work was so remarkable that during the next spring he was allowed to present his research as his doctoral dissertation, "On Induction in Rotating Spheres," and received the degree magna cum laude. He became Helmholtz's assistant at the Physikalisches Institut at the University of Berlin, and during his 3 years there Hertz's most remarkable achievement was his work on the pressure arising between two plates in contact. The influence of his conclusions on the construction of precision instruments was so great that his paper "On the Contact of Elastic Solids" was simultaneously published in a scientific and a technical magazine. But the promise of the future lay with his work on electric and cathode-tube discharge, published in 1883 in two papers.

Hertz next went to the University of Kiel, where he did some work on meteorological and thermoelectric problems, but his real interest was in James Clerk Maxwell's theory as shown by his paper from 1884, "On the Relations between Maxwell's Fundamental Electromagnetic Equations and the Fundamental Equations of the Opposing 'Electromagnetics.'" Hertz was at Karlsruhe as the head of the Physics Institute at the Polytechnic when he began his experimental research on the effect of electric and cathode-tube discharges. In Karlsruhe he met Elizabeth Doll, the daughter of a well-known geodesist, and married her on July 31, 1886.

On surveying the equipment in his laboratory, Hertz came across two Riess spirals and found "that it was not necessary to discharge large batteries through one of these spirals to obtain sparks in the other; ... that even the discharge of a small induction coil would do, provided it had to spring across a spark gap." He soon noticed that the oscillations thus produced were rather regular. By spring 1887 Hertz knew that sparks were more readily formed when the metal spheres forming the gap were exposed to ultraviolet radiation.

This discovery put Hertz within reach of producing with relative ease oscillations of sufficiently high frequency with corresponding wavelengths that could be detected with apparatus tailored to the dimensions of ordinary laboratories. By summer he succeeded in showing the effect of a rectilinear electric oscillation upon a neighboring circuit. On November 10, 1887, he sent to the Berlin Academy the now historic report "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators," disclosing that he had obtained oscillatory inductive action at distances up to 12 meters. While the result was a triumph for Maxwell's theory, Hertz knew that one also had to settle the question of the finite velocity of the propagation of the inductive effect across space. This he did in 1888, and the same year he also proved that electromagnetic waves could be reflected as predicted by Maxwell's theory. Later that year he accepted the chair of physics at the University of Bonn, which had been vacant since the death of R. J. E. Clausius.

Hertz's work at Bonn aimed at a generalization of a cherished idea of his revered teacher, Helmholtz, that electromagnetic effects were products of the motion of the ether atoms, obeying the law of least action. Hertz now wanted a formulation of the whole science of physics along these lines. His Principles of Mechanics took him 3 years to write; it was published posthumously.

In 1889 Hertz was the principal speaker at the Congress of German Scientists at Heidelberg, where he described the impact of the verification of Maxwell's theory on the physics of the future. Needless to say, he believed with the rest of the late-19th-century physicists that it was to become a physics of the ether. Hertz succumbed to an infection of the inner ear on January 1, 1894. Most likely Hertz would have been among the first to perceive the fallacies inherent in the concept of the ether and to usher in a new age of physics.