Did Ancient Humans Have Knowledge of the Electromagnetic (EM) Spectrum? (cont.)
By Glenn Kreisberg, Radio Frequency (RF) Spectrum Engineer
The History and Breakthroughs in the Development of ElectromagneticTheory.
Long before any study of EM fields occurred, Scotsman John Napier, born in 1550, developed the theory of logarithms in order to eliminate the frustration of hand calculations of division, multiplication, squares, etc. We use logarithms every day in EM theory when we refer to the decibel (dB) as a measure of power. When producing and measuring power in decibels, values increase logarithmically by 3, each time you double the power in watts. His “numbering rods,” constructed of ivory, became known as “Napier's Bones,” and comprised the world's first slide rule. Some of his neighbors suggested that he was in league with the powers of darkness... a trait that has often been associated with successful radio frequency and microwave engineering.
Ether was the hypothetical substance through which electromagnetic waves traveled. It was proposed by the Greek philosopher Aristotle (born 384 BC) and used by several optical theories as a way to allow propagation of light, which was believed to be impossible in "empty" space.
It was supposed that the ether filled the whole universe and was a stationary frame of reference, which was rigid to electromagnetic waves but completely permeable to matter. Robert Hooke (1635-1703) endorsed the idea of the existence of the ether in his work Micrographia (1665), and several other philosophers of the 17th century, including Christiaan Huygens, did the same. At the time of James Maxwell's mathematical studies of electromagnetism two centuries later, ether was still assumed to be the propagation medium and was imbued with physics properties such as permeability and permittivity.
In 1887, Albert Michelson and Edward Morley performed a crucial experiment in an attempt to detect the existence of the ether. The experiment, named the Michelson-Morley experiment, shocked the scientific community by yielding results that implied the non-existence of ether. This result was later on used by Einstein to refute the existence of the ether and allowed him to develop special relativity without this artificial (and non-existent) constraint.
Christiaan Huygens (1629-1695) a Dutch physicist, was the leading proponent of the wave theory of light. In Traité de la Luminère (1690), he developed the concept of the wave front. The wave theory was supported by the observation that two intersecting beams of light did not bounce off each other as would be expected if they were composed of particles. In contradiction to Sir Isaac Newton, Huygens correctly believed that light must travel more slowly when it is refracted towards the normal, although, this was not proven until experiments in the nineteenth century.
In 1672, Sir Isaac Newton studied the interaction of visible light with a glass prism and first recognized that white light is actually a mixture of different colors representing the entire visible light spectrum. White light originates from a variety of natural and artificial incandescent sources, including the sun, chemical reactions (such as fire), and incandescent tungsten filaments. The broad emission spectrum from sources of this type is referred to as thermal radiation. Other sources of visible light, such as gas discharge tubes, are capable of emitting light in narrow, well-defined frequency ranges (representing a single color) that depend on specific energy-level transitions in the source material atoms.
Lazzaro Spallanzani, born in 1727 in Italy, had a huge influence on many of the physical sciences, which is even more remarkable because he was an ordained Jesuit priest. Spallanzani is remembered because his Lettere sul volo dei pipistrelli acciecati published in 1794, recorded correspondence about his experiments on the remarkable sense of direction of bats. Bats use sonar to move about in the dark, which some might argue was the inspiration for radar.
In 1767 the English chemist Joseph Priestly (1733-1804) showed that unseen forces followed the inverse square law. Later, the French military engineer Charles Augustin de Coulomb (1736-1806) carried out careful experiments on bodies charged with static electricity, and on magnets, and in 1794 confirmed that the attractions and repulsions followed the inverse square law.
Michael Faraday, born in 1791, is credited as the discoverer of magneto-electric induction, the law of electrochemical decomposition, the magnetization of light, and diamagnetism, among many other contributions to chemistry and physics. Michael Faraday, who did his research at the Royal Academy at London, even went so far as to say that the electromagnetic field was the lowest form of physical reality. Faraday's name is immortalized in the Farad, the unit of capacitance.
In the same year that Faraday made this discovery, Sir James Clerk Maxwell was born in Scotland, the man whose brilliant mathematical interpretation of Faraday's ideas was to become the foundation of our modern concepts of electricity, magnetism and light. He coined the term electromagnetic radiation, which is derived from the characteristic electric and magnetic properties common to all forms of this wave-like energy, as manifested by the generation of both electrical and magnetic oscillating fields as the waves propagate through space.
Maxwell's equations described the fundamental relationship between electricity, magnetism, and wave propagation that underlies all radio and cable communications. Since light and radio waves are the same phenomena, Maxwell’s theories provided the theoretical explanation for why radio waves can be focused and reflected just like light. As he stated in his 1864 work Dynamical Theory of the Electromagnetic Field, "... we have strong reason to conclude that light itself— including radiant heat, and other radiations if any —is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws."
During the next few decades, additional investigations following Maxwell’s lead produced an increasing amount of evidence that electricity and magnetism were very closely related to each other. Heinrich Hertz opened the way for the development of radio, television, and radar with his discovery of electromagnetic waves between 1886 and 1888. He succeeded in generating and performing experiments with electromagnetic waves in 1887, eight years after the death of Maxwell. Hertz produced, detected, and even measured the wavelength (approximately one meter) of radiation that is now classified in the radiofrequency range.
David Hughes, a London-born scientist who was a music professor in his early career, may have actually been the first investigator to succeed in the transmission of radio waves (in 1879), but after failing to convince the Royal Society, he decided not to publish his work, and it wasn't recognized until many years later.
Nikola Tesla is most famous for conceiving the rotating magnetic field principle known as “alternating current,” allowing for the current long-distance electrical transmission system. And interestingly, in Colorado Springs, Colorado, where he stayed from May 1899 until early 1900, Tesla made what he regarded as his most important discovery: terrestrial stationary waves. Through this discovery he proved that the Earth could be used as a conductor and would be as responsive as a tuning fork to electrical vibrations of a certain frequency. He also lighted 200 lamps without wires from a distance of 25 miles (40 kilometers) and created man-made lightning, producing flashes measuring 135 feet (41 meters). At one time he was certain he had received signals from another planet in his Colorado laboratory, a claim that was met with derision in some scientific journals.
And, on a historic day in December 1901, Guglielmo Marconi, determined to prove that wireless waves were not affected by the curvature of the Earth, used his radio system for transmitting the first wireless signals across the Atlantic between Poldhu, Cornwall, and St. John's, Newfoundland, a distance of 2100 miles. In 1912 Marconi patented the first wireless receiver and as they say, the rest is history.