HERTZ, HEINRICH

HERTZ, HEINRICH (1857–1894), German scientist.

Heinrich Hertz's name has been given to a unit of frequency, an honor he received because he was the first person to produce electromagnetic waves (radio waves) artificially and to demonstrate that their behavior is similar to that of light (1886–1888). Hertz and most of his contemporaries considered these experiments the final proof that light is nothing but electrical waves, and more generally a decisive corroboration of James Maxwell's field theories and a rejection of theories such as Wilhelm Weber's, which were based on direct actions at a distance. Settling the long-standing question of the nature of light and electromagnetism earned Hertz a name as one of the leading physicists of his time.

Born in 1857 in Hamburg, Heinrich Hertz studied first engineering and then physics at the Dresden and Munich polytechnic schools before moving to Berlin University in 1878. Here Hermann Helmholtz had developed his own version of Maxwell's theory and tried to design experiments that would favor this theory rather than Weber's. Soon Hertz distinguished himself by solving a prize problem showing that if conduction currents are accompanied by mass transport, the mass is extremely small. With an eye to Hertz, Helmholtz subsequently formulated another prize problem calling for the detection of effects of the so-called displacement current that should exist according to Maxwell's theory. However, Hertz estimated that the chances of a successful outcome of such experiments were slim and instead turned to other problems concerning elasticity and hardness, evaporation, the tides, a new dynamometer, floating plates, and cathode rays, which he incorrectly believed, because of one of his experiments, were electrically neutral (they have since been explained as a ray of electrons). Employed from 1880 as Helmholtz's assistant, Hertz wrote eleven papers on these subjects.

In 1883 he was appointed professor of theoretical physics at Kiel University and the following year he gave a public series of lectures, Modern Ideas on the Constitution of Matter, which anticipated some of his later ideas concerning natural philosophy and the nature of electromagnetism. According to Albrecht Fölsing, who published Hertz's lecture notes in 1999, these lectures show that by 1884 Hertz had completely adapted a Maxwellian point of view and had thought out the oscillator that he later used to produce electrical waves. Jed Buchwald, on the other hand, has argued that Hertz continued to adhere to Helmholtz's electromagnetic theory until he conducted his crucial experiments; this school of thought questions whether Hertz's laboratory equipment of 1886 to 1888 owes much to his thought experiments of 1884.

Hertz again turned to experimental work after he had moved to a professorship at the polytechnic school in Karlsruhe, in 1885. Having accidentally discovered that he could produce fast electrical oscillations in capacitively loaded wires breached by spark gaps, he returned to the problem Helmholtz had posed: detecting the effects of the displacement current. After two years of intensive experimentation, he was able to detect and produce electromagnetic waves.

Hertz left it to Marconi to pursue the technological potentials of his discovery and instead turned to theoretical clarifications of Maxwell's theory for bodies at rest and bodies in motion. His first paper on these matters offers an almost axiomatic presentation of Maxwell's theory and contains Maxwell's equations in the form they continue to be presented. The second paper, based on the assumption that a fictive space-filling medium called the "ether" is dragged by moving bodies, was soon rendered obsolete by Hendrick Lorentz's and Albert Einstein's relativity theories.

The theoretical papers were published after Hertz had moved to a professorship in Bonn, in 1889. His axiomatic presentation did not make any assumptions about the nature of the electromagnetic field, and his remarks that Maxwell's theory is nothing other than Maxwell's equations have even led many physicists to conclude that he found such questions either unimportant or unscientific. However, most modern scholars are of the opinion that Hertz believed that the electromagnetic field should eventually be explained as a state in a mechanical ether and that he thought of his last book, Principles of Mechanics, as the basis for such a reduction of electromagnetism as well as all other natural phenomena to the laws of mechanics.

The book, which can be considered as the last major foundational work in the classical mechanistic tradition, is interesting for physical, mathematical, and philosophical reasons. In the introduction, Hertz explains physical theories as (mental) images of the world (anticipating later ideas about models) and sets up three conditions that are necessary to judge and compare such images. His own image did not base itself on force as a basic concept but relied on hidden masses (the ether?) to produce the effects usually ascribed to forces. It was presented in a differential geometric form that has been imitated in later treatments of mechanics.

Hertz began his work on mechanics in 1891. The following summer he contracted an infection of his nose. The infection gradually worsened and eventually led to his premature death in 1894, shortly before the publication of his last book.

See alsoElectricity; Helmholtz, Hermann; Marconi, Guglielmo; Maxwell, James Clerk; Physics.

bibliography

Baird, Davis, R. I. G. Huges, and Alfred Nordmann, eds. Heinrich Hertz: Classical Physicist, Modern Philosopher. Volume 198 of Boston Studies in Philosophy of Science. Boston, 1998.

Buchwald, Jed Z. The Creation of Scientific Effects: Heinrich Hertz and Electric Waves. Chicago, 1994.

Fölsing, Albrecht. Heinrich Hertz: EineBiographie. Hamburg, 1997.

Hertz, Heinrich. Gesammelte Werke. Vols. 1–3. Leipzig, 1884.

——. Die Constitution der Materie: Eine Vorlesung über die Grundlagen der Physik aus dem Jahre 1884. Edited by Albrecht Fölsing. Berlin, 1999.

Lützen, Jesper. Mechanistic Images in Geometric Form: Heinrich Hertz's Principles of Mechanics. Oxford, U.K., 2005.

Nordmann, Alfred. "Heinrich Hertz: Scientific Biography and Experimental Life." Studies in History and Philosophy of Science 31 (2000): 537–549.

Jesper LÜtzen