4.3.2 Inductive Telegraphy at a Distance
The First Wireless Technology
There are several contenders for the honor of inventing the first wireless radio-frequency communications devices. “The attraction and repulsion of electricity, like those of magnetism, act at great distances,” the American scientist and first director of the Smithsonian Institute, Professor Joseph Henry (1797–1878) affirmed in 1859 [[ii]]. Henry made some of the first experiments with inductive signaling.
In one experiment, he placed a 5 ½ ft diameter coil 7 ft away from a 4 ft diameter coil. When he made intermittent electrical contact between an eight-cell battery (probably ~12 V) and the loop on the right in Fig. 4.32, shocks were detectable by placing the second loop’s terminal wires on his tongue [[iii]]. The loops were aligned as shown along their mutual axes to maximize the extent of the coupling.
In 1842, Henry demonstrated electrostatic induction at a distance, proving that a charged plate on the second floor of his Princeton house could induce sparks from a plate in his basement.
Henry may also be responsible for the first identification of alternating current.
The discharge, whatever may be its nature, is not correctly represented (employing for simplicity the theory of Franklin) by the single transfer of an imponderable fluid from one side of the jar to the other ; the phenomenon requires us to admit the existence of a principal discharge in one direction and then several reflex actions backward and forward, each more feeble than the preceding, until equilibrium is attained [[v]].
This oscillatory resonance behavior is now a well-understood aspect of reactive or AC circuits. Energy transforms back and forth between electric and magnetic forms multiple times, each time losing a bit of the energy to the resistive losses in the discharge. Such “damped resonant” circuits made early radio possible.
Oliver Heaviside’s arch-nemesis, William Preece (1834–1913), experimented with inductive wireless systems and succeeded in transmitting alternating current signals a distance of 3.3 miles from Lavernock Point to Flatholm Island (see Figure 4.34) [[vi]]. Preece employed a two-horsepower generator operating at 192 cycles per second. Attempts to close the link across a distance of 5.35 miles between Lavernock Point and Steepholm Island were unsuccessful–the signal could be heard but not reliably decoded. The transmitting and receiving coils required nearly a mile of wire [[vii]]. In other experiments directed by Preece, Oliver Heaviside’s brother, Arthur, succeeded in carrying on a phone conversation to a colleague 360 feet underground in a mine near Newcastle [[viii]].
In 1885, Lucius J. Phelps (1850–1925) deployed a railway telegraph he invented on the Harlem River branch of the New York, New Haven, & Hartford Railroad Company [[xi]]. A telegraph cable embedded in the track, as in Figure 4.35 (a) coupled inductively to pick-up coils underneath a railway car, as in Figure 4.35 (b). An operator on board the moving train could relay telegraph messages to and from the moving train to nearby stations, as in Figure 4.35 (c). Thomas Edison (1847–1931) promoted a similar venture able to couple into telegraph wires running alongside the track [[xii]], and even proposed ship-to-ship communications [[xiii]]. Sadly for Edison and his partners, businesspeople of the 1880s were not as interested in remaining in constant contact with their offices as their modern counterparts. The technological success proved a business failure. It would be more than a century before cellular telephones made personal communication from trains – or automobiles – ubiquitous.
The Edison or Phelps systems operated over short ranges to wires embedded in the track or alongside the railway. Practical, longer-range communications using inductive-coupling required much larger coils, like those employed by Preece [[xiv]]. These are merely highlights of early wireless technology. There was enough wireless communications progress to fill the pages of Fahie’s History of Wireless Telegraphy by 1901 [[xv]], but widespread commercial success would require moving beyond short-range inductive wireless to long-range radio transmission.
The fluid model of electric circuits cannot readily explain why the resistance of a wire increases with frequency and the current concentrates in the skin of the conductor. It cannot explain how signals reach out and couple between parallel wires or cross the gap between nearby loops or plates. Action is occurring at a distance, but does it just happen? Or is there a physical process involved? Faraday’s concept of a field as perfected by Maxwell and the Poynting-Heaviside theory of energy flow accounts for this wide range of phenomena. The short-range, inductive, wireless links pioneered by Edison, Preece, and others have come to fruition in a wide range of technologies today, including Radio Frequency Identification (RFID), Near-Field Communications (NFC), and Near-Field Electromagnetic Ranging (NFER) [[xvi]].
Next time: 4.3.3 Cross Coupling: Action-at-a-Distance, Like It Or Not!
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References
[i] Fahie, J.J., A History of Wireless Telegraphy, 2nd ed. Revised, New York: Dodd, Mead, and Co., 1901, p. 88.
[ii] Henry, Joseph, Scientific Writings of Joseph Henry, vol. 2, Washington: Smithsonian, 1886, pp. 332-333. See: https://www.google.com/books/edition/Scientific_Writings_of_Joseph_Henry/w6cKAAAAIAAJ?hl=en&gbpv=1&bsq=induction Originally published: “Metrology in Its Connection with Agriculture: Part V – Atmospheric Electricity,” Agricultural Report of Commissioner of Patents for 1859, pp. 461-524.
[iii] Fahie, J.J., A History of Wireless Telegraphy, 2nd ed. Revised, New York: Dodd, Mead, and Co., 1901, p. 88.
[iv] Henry, Joseph, Scientific Writings of Joseph Henry, vol. 2, Washington: Smithsonian, 1886, pp. 332-333. See: https://www.google.com/books/edition/Scientific_Writings_of_Joseph_Henry/w6cKAAAAIAAJ?hl=en&gbpv=1&bsq=induction Originally published: “Metrology in Its Connection with Agriculture: Part V – Atmospheric Electricity,” Agricultural Report of Commissioner of Patents for 1859, pp. 461-524.
[v] Brother Potamian and James J. Walsh, Makers of Electricity, New York: Fordham University, 1909, p. 92.
[vi] Preece, William Henry, “On the Transmission of Electric Signals Through Space,” The Electrical World, September 2, 1893, pp. 179-180. See: https://www.google.com/books/edition/Electrical_World/WNkhAQAAMAAJ?hl=en&gbpv=1&dq=heaviside+preece+telegraph+sending+key&pg=PA179&printsec=frontcover
[vii] Fahie, J.J., A History of Wireless Telegraphy, 2nd ed. Revised, Edinburgh and London: William Blackwood and Sons, 1901, p. 147-150.
[viii] Baker, E.C., Sir William Preece, F.R.S.: Victorian Engineer Extraordinary, London: Hutchinson of London, 1976, p. 257.
[ix] Fahie, J.J., A History of Wireless Telegraphy, 2nd ed. Revised, Edinburgh and London: William Blackwood and Sons, 1901, p. 148.
[x] Staff, “The Phelps System of Telegraphing to and from Railway Trains in Motion,” The Manufacturer and Builder, August, 1885, pp. 173-174.
“Telegraphing to and from Railway Trains in Motion,” The Manufacturer and Builder, vol. XVIII, No. 2, February, 1886.
“A New System of Telegraphing to and from Railway Trains in Motion,” The Manufacturer and Builder, April 1886, pp. 86-87.
[xi] Staff, “The Phelps System of Telegraphing to and from Railway Trains in Motion,” The Manufacturer and Builder, August, 1885, pp. 173-174.
“Telegraphing to and from Railway Trains in Motion,” The Manufacturer and Builder, vol. XVIII, No. 2, February, 1886.
“A New System of Telegraphing to and from Railway Trains in Motion,” The Manufacturer and Builder, April 1886, pp. 86-87.
[xii] Staff, “The Edison System of Railway Telegraphy,” Scientific American, February 20, 1886, pp. 119-120.
“Mr. Edison believes that he has made a new discovery in physics. He finds that bodies hitherto considered non-conductors, such as air, are really so only after an appreciable period of time. At the first instant of discharge, the air offers no resistance to the passage of a current, but becomes almost immediately polarized, and the communication becomes permanently interrupted. The idea, therefore, in these very short waves of high tension is to permit then to cross to the wires before the air has time to offer any opposition. A sufficient period, however, intervenes between them to permit the air to return to its normal condition, and consequently allow the succeeding waves to pass.”
[xiii] Baldwin, Neil, Edison: Inventing the Century, New York: Hyperion, 1995, p. 179.
[xiv] Preece, William Henry, “On the Transmission of Electric Signals Through Space,” The Electrical World, September 2, 1893, pp. 179-180. See: https://www.google.com/books/edition/Electrical_World/WNkhAQAAMAAJ?hl=en&gbpv=1&dq=heaviside+preece+telegraph+sending+key&pg=PA179&printsec=frontcover
[xv] Fahie, J.J., A History of Wireless Telegraphy, 2nd ed. Revised, New York: Dodd, Mead, and Co., 1901.
[xvi] Schantz, Hans G. and James Fluhler, “Near Field Technology – An Emerging RF Discipline,” Keynote Address, Proceedings of The European Conference on Antennas and Propagation:EuCAP 2006 (ESA SP-626). 6-10 November 2006, Nice, France. Editors: H. Lacoste & L. Ouwehand. Published on CDROM, p.2.1. Available from: https://www.researchgate.net/publication/228849384_Near-Field_Technology-An_Emerging_RF_Discipline
I never knew that the wires ran with the railway cars. Such an interesting article!
What do you think of Mahlon Loomis' claims of achieving wireless telegraphy in 1866? Could it have been electrostatic transmission? Or a fluke?