Heinrich Hertz Produces and Detects Radio Waves in 1888
Heinrich Hertz Produces and Detects Radio Waves in 1888
In 1888 German physicist Heinrich Hertz (1857-1894) produced and detected electromagnetic waves in his laboratory. His goal was to verify some of the predictions about these waves that had been made by Scottish physicist James Clerk Maxwell (1831-1879). Of course, simply producing electromagnetic waves was not sufficient unless they could be detected, too. What Hertz did not realize at the time is that his discovery not only verified and validated Maxwell's work, but it also made possible the later invention of radio, television, radar, and other devices that depend on the production and detection of electromagnetic radiation.
Early theories in physics assumed that all actions required some sort of direct contact or influence to make things happen. A hand pushing a ball or a wall stopping a ball are examples of this. However, gravity and magnetism seemed to violate this concept by seemingly allowing action at a distance without direct physical contact between objects. This led to speculation that various "ethers" existed that filled space so that, for example, magnetic forces would act on the ether that would, in turn, act on a piece of iron to pull it towards the magnet. By the mid-1800s, physicists had developed a theory involving separate ethers for the transmission of heat, gravity, static electricity, magnetism, and other phenomena that seemed to embody action at a distance.
In the 1840s Michael Faraday (1791-1867) developed the concept of a physical field in which each point had specific properties relating to forces acting on bodies within that field. A gravitational field, for example, is defined by the strength of the gravitational force and its direction at every point in the field. At the surface of the earth, the gravitational field points directly at the center of the earth with an acceleration of 9.8 meters per second per second (a force of one gravity). Electrical and magnetic fields are similar in nature.
The next step was made in the 1860s by Maxwell, who showed that electricity and magnetism are related and that interactions between these two forces will produce what is called electromagnetic radiation. First, Maxwell showed that light is a form of electromagnetic radiation. By explaining heat as a form of electromagnetic radiation similar to light, Maxwell was able to combine many of the ethers into one—the one he thought was needed to transmit electromagnetic waves. (We now know this ether is not present, as shown in 1887 by the Michelson-Morley experiment.) At the same time, Maxwell's equations suggested that electromagnetic radiation could have either longer or shorter wavelengths than light.
Maxwell developed one of several competing theories involving fields to explain electrical and magnetic action at a distance. Others were developed by Helmholtz, Faraday, and Wilhelm Weber (1804-1891). Studying each of these theories in turn, Hertz saw some similarities that apparently escaped other physicists of the day, leading him to speculate about the nature of electromagnetism. While working with equipment designed to test some properties of electromagnetic fields, Hertz accidentally developed a crude oscillating circuit that transmitted electromagnetic energy to a similar circuit used as a monitor. Eventually Hertz realized that these devices could be used to reliably produce and detect oscillating electromagnetic waves—radio waves—that traveled through space.
The lasting importance of Hertz's discovery cannot be overstated. Consider the use to which radio and other electromagnetic waves are put today: radio, television, radar, food preparation, welding, heat sealing, magnetic resonance imaging, radio astronomy, and navigation are only a few of the applications.
It should be noted, however, that radar waves are generated in a different manner than are radio waves. Specifically, radio waves are generated by inducing electromagnetic oscillations in an antenna that are then broadcast to distant receiving stations. By contrast, radar waves are generated in a device called a cavity magnetron that is very different from an antenna. However, radar (an acronym for radio detection and ranging) is possible without this device, and, in any event, without having first discovered how to produce and detect radio waves, radar would not have been possible at all. Similarly, the widespread use of radio waves for communication across long distances depended on the invention of the vacuum tube in 1907 by Lee De Forest (1873-1961). But the discovery of ways to generate and receive radio waves was still a necessary prerequisite for radio communications.
The impact of Hertz's discovery is easily recognized in the following categories of use: communications, science, industry, and military.
The most obvious impact of generating and receiving radio waves is in communications. Although not originally envisioned by Hertz, it took only six years for Italian engineer Guglielmo Marconi (1874-1937) to construct a simple device that used radio waves to ring a bell. In 1901 Marconi successfully received a radio transmission sent from England in Newfoundland. Transmission of voices and music by AM radio followed in 1906, less than 20 years after Hertz's initial success. Other inventions followed, including television, communications satellites, and so forth, each simplifying a formerly difficult task—staying in touch over long distances. Prior to radio, communication beyond one's town was difficult and, for most people, rare. Hertz, while not directly involved in changing this, certainly took the first steps by showing it was possible to generate and receive waves that could travel so far so quickly. It may be a cliché to say that radio and television have made the world a smaller place, but it is a cliché because it is true.
The arena of science was profoundly affected by Hertz's discoveries as well, and in a number of ways. At the time he announced his results, they had the effect of stimulating research into many aspects of electrodynamics and electromagnetism. This, in turn, contributed to the revolution in physics that was already looming on the horizon. Hertz died before the landmark discoveries that initiated this revolution, but his work was important. Radio astronomy, which has taught us much about the nature of the universe, is entirely dependent on receiving and interpreting radio waves from outer space. Our current theory of the formation of the universe, the Big Bang theory, was strengthened immeasurably by the discovery of the cosmic microwave background radiation field, discovered as a result of investigations into improving radio communications. Much medical research and treatment utilizes magnetic resonance imaging (MRI) that uses radio waves as part of the imaging process. Radar waves, a form of radio frequency radiation, have been bounced off the moon, Venus, Mercury, and a number of asteroids to learn their distances and to map their surfaces. Radar is also used extensively in weather research, helping to predict and analyze incipient storms. And, of course, deep-space probes convey their information and receive instructions via radio signals.
In industry, radio and other electromagnetic waves are used frequently, too. Microwave ovens use radio-frequency radiation to cook food, while other microwave devices are used to weld plastics, and seal bags. The use of radar for air traffic is well known, of course, as is its use for police speed traps. Radio frequency radiation is also used for joining metals in some industries.
Finally, there are innumerable military uses of electromagnetic radiation. One unintended outcome of developing radio communications was to take a great deal of authority and autonomy away from ships' captains. Previously, a captain at sea was almost a minor deity, alone in command of his ship and able to use his full discretion in carrying out his orders. The implementation of radio contact enabled his superiors to remain in contact at virtually all times, following his progress, second-guessing his decisions, giving additional instructions, and so forth. Losing this degree of autonomy upset many captains, but the strategic and tactical advantages overshadowed this, and the ability to coordinate the actions of many ships over thousands of square miles of ocean were immense. The development of smaller radio sets brought these same advantages to the battlefield, changing the nature of warfare and leading to today's emphasis on battlefield information. Add to that the uses to which the military has put radar (detection of enemy units, proximity fuses, electronic countermeasures, to name but a few) and it is apparent that electromagnetic radiation is fundamental to today's military forces worldwide.
In summary, the societal impacts of Hertz's research came quickly, were far-reaching, and may be considered ongoing if taking into account the still expanding fields in which radio, radar, and other high-frequency electromagnetic radiation are used. While not as powerful as the development of electronics, it can be argued that radio has transformed more lives than electronics because of the relative ubiquity of radios compared to computers in the world. Virtually every person in the world has reasonable access to radios (excepting, of course, the small percentage of people who live in very remote and primitive areas); the same can hardly be said of computers. Indeed, the most important indication of the importance of radio to modern society lies in the degree to which we take it for granted. Few question the ability to turn on the radio to hear music or news. Picking up a cordless telephone, a cellular phone, or a walkie-talkie are routine events for most, and we accept as routine that we can see news or sporting events occurring anywhere in the world in real time. Any of these technological commonplaces would have been considered minor miracles prior to Hertz's discoveries.
P. ANDREW KARAM
Buchwald, Jed. The Creation of Scientific Effects: Heinrich Hertz and Electric Waves. Chicago: University of Chicago Press, 1994.
Hellemans, Alexander, and Bryan Bunch. The Timetables of Science. New York: Simon and Schuster, 1988.