by Vaclav Smil
FIGURE 5.16. James Clerk Maxwell (left) postulated the existence of electromagnetic waves longer than light but shorter than sound more than two decades before Hertz’s experiments confirmed the theory. Photo from author’s collection. This portrait of David Edward Hughes (right) was taken during the mid-1880s, just a few years after his pioneering experiments with “aerial electric waves.” Photo courtesy of Ivor Hughes.
Or more precisely, before somebody did so and published the results, because here I must make an important detour in order to describe one of the most remarkable cases of lost priority and misinterpreted invention. Sometime in December 1879, seven years before Hertz began his experiments, David Edward Hughes (1831–1900), a London-born physicist who returned to the city from Kentucky, where he was a professor of music as well as physics, began sending and receiving electromagnetic pulses over distances of as much as several hundred meters (Hughes 1899; figure 5.16). As already noted, Hughes was, in 1878, one of the inventors of a loose contact microphone, and experiments with this device led him to suspect for the first time the existence of what he called “extra current” produced from a small induction coil.
He found that microphones made sensitive receivers of these waves, and he tested the transmission first indoors over distances of up to 20 m; then, walking up and down Great Portland Street with the receiver in his hand and the telephone to the ear, he could receive signals up to 450 m away. Between December 1879 and February 1880 eight people, most of them members of the Royal Society, witnessed these experiments, but George Gabriel Stokes (1819–1903), famous Cambridge mathematician and a future president of the society, concluded that everything could be explained by well-known electromagnetic induction effects. Although Hughes continued his experiments, he was so discouraged by his failure to persuade the Royal Society experts “of the truth of these aörial electric waves” that he refused to write any paper on the subject until he had a clear explanation of their nature, a demonstration that came from Hertz’s experiments.
Crookes, who witnessed the December 1879 experiment, wrote two decades later to Fahie that “it is a pity that a man who was so far ahead of all other workers in the field of wireless telegraphy should lose all credit due to his great ingenuity and prevision” (Fahie 1899:305). How far ahead? A writer in The Globe of May 12, 1899 (cited in Fahie 1899:316), summed up this best when he said that the 1879 experiments “were virtually a discovery of Hertzian waves before Hertz, of the coherer before Branly, and of wireless telegraphy before Marconi and others.” Incredibly, a few years after Hughes’s first broadcasting experiments, there was another near-discovery by none other than Thomas Edison, and it actually went public. One of the world’s great missed fundamental discoveries was a small item displayed in 1884 in a corner of the Philadelphia Exhibition’s largest electrical exhibit, which belonged, predictably, to Thomas Edison: it was an “apparatus showing conductivity of continuous currents through high vacuo.” In its patent application, filed on November 15, 1883, Edison (1884:1) noted that
if a conducting substance is interposed anywhere in the vacuous space within the globe of an incandescent electric lamp, and said conducting substance is connected outside of the lamp with one terminal, preferably the positive one, of the incandescent conductor, a portion of the current will, when the lamp is in operation, pass through the shunt circuit thus formed, which shunt includes a portion of the vacuous space within the lamp.
This device became known as a tripolar incandescent lamp, but the observed phenomenon, called by Edison etheric force and commonly known as the Edison effect, remained just a curiosity without any practical applications. Another 12 years had to pass after Edison secured this useless patent before the current passing through the vacuous space was recognized as electromagnetic oscillations at wavelength far longer than light but far shorter than audible sound. Interestingly, neither Edison, who through his long career experienced a full measure of triumphs and failures stemming from his obsessive inventive drive, nor Hughes, who ended his life as one of the most honored inventors of his generation, regretted their near misses.
Hughes’s 1899 correspondence with Fahie reveals a man who looked back without bitterness, crediting Hertz with “a series of original and masterly experiments.” And they, done between 1886 and 1889 without any knowledge of Hughes’s work, were exactly that. Heinrich Rudolf Hertz (1847–1894; figure 5.17) was steered in the direction of these fundamental experiments by his famous teacher, Hermann von Helmholtz (1821–1894). In 1879 Helmholtz made an experimental validation of Maxwell’s hypotheses the subject of a prize by the Berlin Academy of Sciences, and he believed that Hertz would be the best candidate to solve the problem. Although Hertz soon abandoned this line of inquiry, his “interest in everything connected with electric oscillations had become keener” (Hertz 1893:1).
FIGURE 5.17. Heinrich Hertz’s experiments opened the way for the entire universe of wireless communication and broadcast information. Simplicity of his epochal discovery is best illustrated by one of his early instrumental arrangements (right). An inducing circuit (top) contained the induction coil (A) and straight copper wire conductors (C and C’) with the discharger (B) at the center; the induced circuit was a rectangular wire with the gap adjustable by a micrometer (M). Reproduced from Hertz (1887).
Hertz finally began investigating what he termed sehr schnell elektrische Schwingungen (very rapid electric oscillations) in 1886 at the Technische Hochschule in Karlsruhe (where two decades later Fritz Haber made another epochal discovery, that of ammonia synthesis from its elements). His experimental setup was very simple, and all of his work is well documented in his diaries, letters, and papers (Hertz 1893; Hertz and Susskind 1977). He produced electromagnetic waves by using a large induction coil, basically a transformer that received pulsed voltage from batteries to the primary winding and produced a much higher voltage in the secondary winding. In his first set of experiments, he used a straight copper wire with a small discharge gap for the inducing circuit and a rectangle of insulated wire for the induced circuit (figure 5.17). Subsequently, his discharger consisted of a straight copper wire 5 mm in diameter with a 7.5 mm spark gap in the middle that was attached to spheres 30 cm in diameter made of sheet zinc and placed 1 m apart. Once this simple dipole antenna was connected to an induction coil, its alternate charging and discharging produced sparks across the gap. His secondary circuit was even simpler, what we came later to call a loop receiving antenna, without any rectifier or amplifier, just a coil of wire 2 mm thick formed in a circle of 35 cm in radius left with just a small spark gap that could be regulated by a micrometer screw (Hertz 1887). Hertz set up all the experiments in such a way that the spark of the induction coil was visible from the place where the spark in the micrometer took place.
The most important reason for Hertz’s success was his choice of frequencies. All of his experiments were done in a lecture room 15 m long and 14 m wide, but rows of iron pillars reduced the effective area to about 12 × 8 m. This meant that in order to radiate the waves from one end of the room, bounce them off a metal sheet at the other end, and measure the crests or nodes of the standing waves (by the strength of sparks) at least one half wavelength (and preferably several) had to fit into the length of the room. Hertz understood this requirement, and the best reconstruction of his experiments indicates that he was using wavelengths between 6 m and 60 cm, that is, frequencies of 50–500 MHz. His ingenious experiments proved that these invisible electromagnetic waves behave much as light does as they are reflected and refracted by surfaces and that they travel through the air with finite, lightlike velocity. In retrospect, the discovery of the waves that “range themselves in a position intermediate between the acoustic oscillations of ponderable bodies and the light-oscillations of the ether” (Hertz 1887:421) was obviously one of the most momentous events in history.
Hertz’s feat was akin to identifying a new, enormous continent that is superimposed on a previously well-explored planet, accessing an
invisible but exceedingly bountiful realm of the universe, the existence of an entirely new phenomenon of oscillations. Less than a decade after Hertz’s experiments came the first wireless telegraph transmissions, and less than two decades later the first radio broadcasts. By the late 1930s, radio was the leading means of mass communication and entertainment, the first scheduled television broadcastswere taking place, and radar was poised to become a new, powerful tool in warfare and, after WWII, also in commercial aviation. By the century’s end, Hertzian waves had changed the world, and there is yet no end to their impact: their subdivision, modulation, transmission, and reception for the cellular telephony and wireless WWW are just the latest installment in the still unfolding story.
But Hertz did not foresee any practical use of his invention, and because of his premature death, he never got a chance to revise this conclusion once research into the communication with high-frequency waves got underway. The process that transformed Hertz’s discovery into a new inexpensive communication technique that eventually reached all but a very small fraction of the world’s population is an even better example of a collectively created innovation than is the creation of first electricity-generating and transmission systems. Although there can be little doubt that such systems would have emerged sometime during the 1880s or the 1890s, even without Edison, his drive, determination, and holistic approach had significantly speeded up the process. In contrast, none of the principal contributors to the development of radio occupies a similarly indisputable pivotal position, because no individual carried the invention from the basic investigation of newly discovered waves to commercial broadcasts.
Wireless Communication
Guglielmo Marconi’s (1874–1937; figure 5.18) fame rests on filing the first wireless telegraph patent in 1896 (G.B. Patent 7,777; U.S. Patent 586,193), and being the first sender of wireless signals over increasingly longer distances and finally across the Atlantic in 1901 (Boselli 1999; Jacot and Collier 1935; Marconi 1909). But, David Hughes aside, there are at least four other pioneers of wireless telegraphy whose work made Marconi’s achievements possible, or preceded his first broadcasting demonstrations. In 1890 Nikola Tesla’s invention of his eponymous coil, the device that could step up ordinary currents to extremely high frequencies, opened the way for transmission of radio signals (Martin 1894). In 1890 Edouard Branly (1844–1940) noticed that an ebonite tube containing metal filings that would not normally conduct when placed in a battery circuit became conductive when subjected to oscillatory current from a spark generator. This device made a much better detector of electromagnetic waves than did Hertz’s spark gap.
In June 1894, at the Royal Institution, and again in August in Oxford, Oliver Joseph Lodge (1851–1940; see figure 6.3) used an improved version of Branly’s tube, which he named coherer in order to demonstrate what might have been the world’s first short-distance wireless Morse broadcasts (Jolly 1974). Nature reported on the first event, and in 1897 Lodge recalled that on the second occasion, when signals were sent some 60 m (and through two stone walls) from the Clarendon Laboratory to the Oxford Museum, he used Morse signals. On balance, Aitken (1976) believes that Lodge, not Marconi, was the inventor of wireless telegraphy. But Lodge himself acknowledged that “stupidly enough no attempt was made to apply any but the feeblest power so as to test how far the disturbance could really be detected” (Lodge 1908:84). He, much like Hertz, had a purely scientific interest in the matter and took steps to the first commercial steps only after Marconi’s 1896 patent.
FIGURE 5.18. Guglielmo Marconi, who, without a formal scientific or engineering education, put into practice what several much more experienced men only contemplated doing: sending and receiving wireless signals by using a simple patented apparatus. This photograph was taken in 1909 when Marconi’s work was rewarded by a Nobel Prize in physics. Photograph © The Nobel Foundation.
And yet already two years before Lodge’s London and Oxford demonstrations, William Crookes—who also witnessed Hughes’s 1879 experiment, and whose concerns about the world food production that he expressed in 1898 were noted in chapter 4—spelled out (albeit still timidly, as his vision was limited to Morse signals) commercial potential of Hertzian waves. He noted that
an almost infinite range of ethereal vibrations or electrical rays … un-folded to us a new and astonishing world—one which it is hard to conceive should contain no possibilities of transmitting and receiving intelligence … Here, then, is revealed the bewildering possibility of telegraphy without wires, posts, cables, or any of our present costly appliances … This is no mere dream of a visionary philosopher. All the requisites needed to bring it within the grasp of daily life are well within the possibilities of discovery … (Crookes 1892:174, 176)
And Russian historians routinely claim that the inventor of wireless telegraphy is Alexander Stepanovich Popov (1859–1906), who began his work with electromagnetic waves as he tried to detect approaching thunderstorms (Radovsky 1957). He designed an improved version of Lodge’s coherer and used a vertical antenna to pick up the discharges of atmospheric electricity. In his lecture to the Russian Physicist Society on May 7, 1895, Popov reported that he transmitted and received wireless signals over the distance of 600 m (Constable 1995). Popov’s first public demonstration of wireless transmission took place in March 1896, and a year later he installed the first ship-to-shore link between the cruiser Africa and the Russian Navy headquarters in Kronstadt.
While none of these four inventors pushed for commercialization of their discoveries, 22-year-old Marconi came to England from Italy in 1896 with determination to patent the achievements of his Italian work and to commercialize his system of wireless telegraphy (Boselli 1999; Jacot and Collier 1935). He arrived in February 1896, and on March 30 (helped by his cousin Henry Jameson-Davis: Marconi’s mother was Annie Jameson, a daughter of the famous Irish whiskey maker who married a well-off Bolognese merchant and landowner) he got a letter of introduction to William Preece, chief engineer of the British Post Office (Constable 1995). What Marconi brought to England was nothing fundamentally new: his transmitter was a version of high-frequency oscillator originally developed by his mentor Augusto Righi (1850–1920) in Bologna, his receiver was an improved version of Branly’s coherer, and his antenna was of grounded vertical type.
What was decisive was his confidence that this system will be, with improvements, eventually able to send signals across long distances and his determination to achieve this goal in the shortest possible time. As Preece correctly observed in an 1896 lecture, many others could have done it, but none of them did (Aitken 1976). Marconi’s preliminary British patent application was filed in London on June 2, 1896, and the first field tests sponsored by the Post Office were done on the Salisbury Plain, where in September 1896 he transmitted 150 MHz signals over the distance of up to 2.8 km. His U.S. patent application was filed on December 7, 1896 (figure 5.19). In the same month, after his signals crossed 14 km of the Bristol Channel, Marconi incorporated the Wireless Telegraph and Signal Co. and began to look for the best possible markets for his system. In September 1899 his signals spanned 137 km across the English Channel between Wimereux and Chelmsford. This achievement convinced Marconi that the signals follow Earth’s curvature, and by July 1900 the directors of his company approved the ultimate trial of trans-Atlantic transmission.
FIGURE 5.19. Illustration of the transmitting component of Marconi’s pioneering patent (U.S. Patent 586,193) for sending and receiving electrical signals. Fig. 1 is a front elevation and Fig. 2 a vertical section of the transmitter with parabolic reflector (a is a battery, b a Morse key, c an induction coil, and d metallic balls). Fig. 2a is a longitudinal section of the oscillator.
John Ambrose Fleming (1849–1945) became the scientific adviser of the project, and he built a new, more powerful transmitter while Marconi himself designed the spectacular inverted wire cone antenna with 60 m diameter to be suspended in a ring of 20 60-m-tall wooden masts. The site selected for the transmitt
er, an alternator driven by an 18.7-kW oil engine whose output was transformed to 20 kV, was at Poldhu in Cornwall, where construction began in October 1900, and Marconi’s mast at Cape Cod was to be the receiver. Setbacks delayed the first attempt: a nearly completed Poldhu aerial collapsed on September 17, 1901, and on November 26, 1901, a gale took down the Cape Cod aerial as well. But Marconi quickly redesigned the Poldhu transmitter, an inverted wire pyramid anchored by four 60-m wooden towers, and decided to shorten the distance and to build a new receiving station on Signal Hill that overlooks St. John’s Newfoundland, 2,880 km from Poldhu.
The first trans-Atlantic signal, sent by the most powerful spark transmitter of that time, was picked up on December 12, 1901, on the simplest untuned receiver (figure 5.20): Marconi heard faint triple dots of Morse S at 12:30 and then again at 1.10 and 2.20 P.M., but nothing afterward. He hesitated before releasing the information to the press four days later. The news was greeted with enthusiasm in both Ottawa and New York, but there was also skepticism about the claim, and some of it remains even today. Major uncertainty surrounds the actual wavelength of the first transmission. Immediately after the event, Marconi claimed it was about 800 kHz; he did not quote any figure in his Nobel lecture, but in his later recollections, in the early 1930s, he put it at about 170 kHz (Bondyopadhyay 1993).