Going Wireless In 1880
In September 1996 AT&T spun off its research arm, Lucent Technologies, as a separate entity. The new company, which began business as one of the nation’s 50 largest, inherited the famous Bell Laboratories as well as AT&T’s operations in fiber-optic, wired, and wireless communications equipment. To link the company’s innovative past with its promising future, Lucent placed on its stock certificates a drawing of Alexander Graham Bell’s photophone, a wireless telephone that used sound to modulate a beam of light. In a press release Lucent said that Bell had considered the photophone his “greatest invention … greater than the telephone.” What was this marvelous, obscure device? And what relation does it have to today’s high-tech communications services?
Bell, originally a teacher of the deaf, had spent several years in the early and mid-1870s developing his telephone with Thomas A. Watson. In March 1876, a few days past his twenty-ninth birthday, he was granted a patent that would make him as rich as any of today’s Internet moguls. With that invention in the hands of corporate executives, Bell could do whatever he chose for the rest of his life. He spent as much time as he could at his home in Washington, D.C., with his new family—his wife, Mabel, a deaf former student of his whom he had married in July 1877, and their daughter Elsie. But scientific research was the other great love of Bell’s life, and an equally demanding one. In the late 1870s, as his business associates feverishly strung telephone wires across the country, his chief scientific pursuit involved searching for a way to communicate electrically without wires.
Inspired by geographers who had made precise measurements by sending electric currents through earth or water, Bell first devised an experimental system for communicating between two boats, a long-standing challenge to telegraphers. As early as 1842 Samuel F. B. Morse had created a closed-circuit wireless telegraph using water as a conductor, and Bell’s idea was a refinement of that invention. He made a small-scale test of his system in 1878 or 1879, but as he later recalled, “At the farthest distance tried—which appeared from the map to be about one mile and a quarter—the sounds produced by the action of the interrupter were distinctly but feebly heard. The experiment was not so successful when tried in salt water.”
Then Bell learned that Professor John Trowbridge at Harvard was developing similar apparatus, so he ceased his natural-conduction wireless experiments. Trowbridge later declared this experimental route to be a technological dead end. In the meantime Bell developed the idea of transmitting and receiving sound with a beam of light, and over the next two years he and Charles Sumner Tainter, a former maker of optical instruments from Watertown, Massachusetts, devoted virtually all their efforts to this goal.
It was well known at the time that the electrical resistance of selenium is reduced when a light shines on it. Therefore, if a piece of selenium forms part of a circuit, the current flowing through it should increase or decrease as the light shining on the selenium is made stronger or weaker. Bell had learned about selenium and its properties on a trip to England in 1878. He realized that if he could devise a way to modulate light intensity with sound waves, he could insert a piece of selenium in a telephone circuit, aim the light at the selenium, and reproduce the sound.
Bell and Tainter’s first design used a pair of rectangular glass plates scored with narrow slots to modulate the intensity of a beam of light. (Artificial sources of light, such as the oxyhydrogen flame and the kerosene lamp, were available, but sunlight was the most convenient for outdoor use.) The slots on the plates were aligned so that the light could shine through them. The first plate was stationary, while the second was attached to the center of a thin diaphragm on the mouthpiece. When sound waves entered the mouthpiece, the vibrating diaphragm caused the second plate to vibrate, altering the alignment of the slots. This changed the amount of light that was transmitted. The system worked better with pure tones and music than it did with speech.
In December 1879 Bell and Tainter sketched out a new and better design. Early the next year they began experiments with it in their laboratory at 1325 L Street in Washington while continuing to work with the slotted transmitter and other variations. The new transmitter consisted of an acoustic telephone mouthpiece with a thin, dimesized diaphragm made of silver-coated glass. A set of lenses focused a beam of light on the vibrating diaphragm, which reflected the beam of light through another set of lenses on its way to the receiver. This was a parabolic reflector of silver-coated copper that collected the transmitted light (which had been dispersed somewhat by the atmosphere) and concentrated it onto a selenium cell placed at its focal point. The selenium cell was wired in circuit with a tray of batteries and a telephone earpiece.
In operation, sound pressure from the mouthpiece caused the reflective diaphragm to vibrate, changing its shape slightly and thus modulating the intensity of reflected light. If the transmitter and receiver were kept in precise alignment, the modulated beam of light would modulate the resistance of the selenium cell, which in turn would modulate the current in the telephone circuit, creating sound.
Bell and Tainter also built an acoustic photophone that required no electricity. In this version, as before, a modulated beam of light was focused onto a receiver. Instead of controlling the flow of electricity through a telephone circuit, however, the rapidly varying light beam caused a sample of a substance to minutely vibrate. These vibrations could be heard with a tube resembling an ear trumpet. Selenium worked with this method, but so did just about everything else Bell and Tainter tried, including gold, silver, mica, glass, potassium iodide, sulfur, several types of rubber, ivory, wood, a tube of cigar smoke, and even an unsmoked cigar.
The range at which the acoustic photophone could be heard was much less than that of the electrical device. Twenty feet or so was the maximum for most substances, and some worked only within a few inches. At such close quarters, it would have been hard to distinguish transmitted sounds from the original voice of the speaker heard through the air. Bell and Tainter solved this problem by transmitting musical tones instead of speech. They synthesized these tones by interrupting the beam of light with a rapidly spinning perforated wheel. With this arrangement, no sound was created at the transmitter, only at the receiver. If the researchers could detect even the faintest of tones, they knew they were hearing a successful photophonic transmission.
The receiver was a brass cone whose inside was stuffed or coated with the material being tested. The apex of the cone was attached to a metal tube whose narrow end could be inserted in the listener’s ear. Bell wrote in 1881 that with certain materials, “The sound was so loud as to be actually painful to an ear placed closely against the end of the hearing-tube.” Experimentation showed that porous and spongy materials were better at photophonic reproduction than compact solids and that dark-colored substances worked better than light or transparent ones. Lampblack gave the best results of all. When Bell and Tainter took the lampblack receiver outdoors, they transmitted speech audibly at distances up to 130 feet. Bell suggested that the range could have been extended farther if they had not had difficulty focusing the beam of sunlight.
Apocryphal accounts place the perfection of the photophone on February 15, 1880, coinciding with the birth of Bell’s second daughter. It has even been said that he wanted to name the child Photophone until his wife convinced him that Marian might be more suitable. This is charming folklore, and Bell’s notes and correspondence do indicate his spending long hours in the laboratory during this period, but the two milestones probably did not happen on the same day.
Tainter’s notebook places the conclusive experiment on February 19, stating: “The first Electric Photophone was completed today about four o’clock and was tried with success.” The record is not clear on which version this was, though researchers at the Smithsonian Institution, where Bell’s model and many associated documents are deposited, believe it was the slotted, or grating, photophone. Further progress was rapid, and one day that spring Tainter took the transmitter to the roof of the Franklin School, an imposing structure two blocks southeast. Bell remained in the lab with the receiver pointed out the window. Tainter recalled that he said, “Mr. Bell, if you hear what I say, come to the window and wave your hat.” Bell complied. Shortly afterward Bell wrote jubilantly to his father: “I have heard a ray of the sun laugh and cough and sing!”
While enthralled with the photophone, Bell balanced his scientific enthusiasm with devotion to his family. When Mabel went to Atlantic City on holiday in late May, he wrote to her almost daily from Washington, discussing both family matters and the progress of his experiments. On May 31, the day he tested the basic apparatus disclosed in his patent application, he exclaimed, “I am afraid that I have nothing to tell you except Thotophone—Photophone—Photophone.’ ” Three days later he wrote, “I have somewhere in the other room a piece of paper filled with headings of subjects to write to you about … but I cannot find it just now and Photophony has driven everything else out of my head.”
Modifications and improvements continued through the summer, interrupted briefly at the end of June when Bell fell ill with a fever and the laboratory building developed drainage problems. By August 27 he was ready to present his results at the American Association for the Advancement of Science meeting in Boston. The next day he applied for a U.S. patent, the first ever for a wireless telephone.
In October Bell traveled to France to receive the Volta Prize for his invention of the telephone. He carried the photophone with him and demonstrated it, to the delight of Continental electricians and scientists. Next he went to England, where he made presentations to the Royal Society, the Society of Arts, and the Society of Telegraph Engineers. He also set up a laboratory in France, where he continued his experiments with remarkable results.
Pre-eminent European scientists, including John Tyndall, William Henry Preece, Ernest Mercadier, and Wilhelm R’f6ntgen, conducted photophonic experiments of their own and published the results. By the early 188Os Bell had begun to refer to his work more generally as the production of sound by “radiant energy” rather than “light energy.” Mercadier suggested that the teleradiophone, or simply radiophone, might be a more appropriate name for the device, and many in the scientific community adopted the latter term. Bell preferred the original name but sometimes referred to his researches in the field of “radiophony.” This was the origin of the term radio in reference to wireless electric communications.
Bell returned to America in 1881. That spring he and Tainter continued their research with light-induced vibrations in a wide variety of materials. They also performed a series of experiments with prisms to break up light into its spectral components. The purpose of this work was to see if certain parts of the spectrum transmitted more efficiently than others. On April 2 Tainter recorded in his notebook: “Have succeeded in obtaining sounds through the whole length of the visible spectrum of the sun, with the exception of the extreme violet rays.… The sounds were not only heard from the visible rays, but also from the invisible rays, beyond the red end of the spectrum.” He and Bell called this version the spectrophone, and beginning in the 1970s it would find scientific application in the field of photoacoustic spectroscopy. For his research in photophony, Tainter received a gold medal at the Paris Electrical Exhibition of 1881.
As an experiment the photophone was a success. As a business proposition, however, it was much less so. Bell had signed over all commercial rights to any of his telephonic inventions to a corporation he had set up, the American Bell Telephone Company. Its executives saw no immediate way to turn the photophone into a profitable device. The Lucent press release explains the device’s limitations: “While Bell was able to demonstrate speech transmission over distances of several hundred feet [the maximum was 700 feet], his idea never attained practical importance because the only transmission medium then available was open air, which is notoriously inhospitable to lightwaves.” Nearly a century later, in fact, attempts to develop atmospheric laser-based communications systems ran into the same problem, leading to renewed interest in optical fibers (see “How We Became Wired—With Glass,” Invention & Technology , Winter 2000).
Bell seems to have been so disgusted by the company’s failure to develop the photophone that he gave up all involvement with telephones and American Bell. But Mabel told a different story, one having to do with her deafness and his affection. In a letter to a friend shortly after her husband’s death in 1922, she wrote: “I verily believe that the reason Dr. Bell did not follow up his invention of the photophone … and the reason he took up aviation instead was that I could not hear what went on over the radiophone but that I could see the flying machine.” This may have been true, but Bell did not abandon his acoustic experiments immediately. He and Tainter, along with Bell’s cousin Chichester Bell, went on to invent the graphophone, a sound-recording device that competed with Thomas Edison’s phonograph in the 1880s. Tainter and Chichester Bell later developed the Dictaphone, a successful office sound recorder.
Despite the company’s dim view of the photophone’s commercial possibilities, ABT’s scientists pursued a limited program of experimental work and continued applying for patents until 1897. The company displayed a version of the device at the 1893 World’s Columbian Exposition in Chicago alongside Bell’s original 1876 telephone and the latest automatic exchange equipment. A different model of the photophone, using a searchlight as an energy source, was unveiled at the 1904 St. Louis World’s Fair.
Eventually Bell’s love for his family and his enthusiasm for other pursuits, such as education for the deaf, the National Geographic Society, and Science magazine, consumed his time. He gave the original photophone to the Smithsonian Institution but continued to lecture on the subject until at least 1896. There is no evidence that American electricians and scientists spent a substantial amount of time in photophonic research.
Elsewhere in the world, however, researchers came up with many improvements to the photophone, stretching into the first decade of the twentieth century. The Brazilian wireless pioneer Roberto Landell de Moura had learned of Bell’s invention while studying physics in Rome during the mid-1880s. Landell incorporated acoustic and electric photophones, as well as a crude Hertz-type transmitter, into a wireless telephone for which he received patents in both Brazil (1901) and the United States (1904). The German scientist Ernst Ruhmer documented European work during this period in detail.
Ruhmer used searchlights with focusing lenses to cover distances up to a mile and a half. Atmospheric distortion was a big problem; Ruhmer mentioned that “at distances such as these, the spreading of light from the searchlight is very considerable, the diameter of the beam being as much as several hundred meters.” Nevertheless, using precise alignment calculations, improved lenses, and oversized parabolic reflectors to catch the beam, Ruhmer continued to transmit to greater distances, even at night.
He ended his photophonic work abruptly in 1903 for political rather than scientific reasons: “It was hoped to continue the experiments as far as the water tower in Steglitz (20 km.), or even to Marienberg … a distance of 37 km., but they had to be broken off because the searchlight was required for use in the [military] operations in South-West Africa.” Ruhmer also invented a photographophone, an apparatus to capture photophonic transmissions on photographic film so that sounds could be reproduced. Bell had sketched something similar in his notebook in 1880 but never got around to testing it.
After Bell and Tainter, Ruhmer achieved the most with the technology. He was the last important researcher to work with the photophone, since the dawn of the twentieth century brought with it a new and much more powerful form of wireless communication, the technology now known as radio. With its immense transmission range and much greater resistance to atmospheric effects, radio was vastly superior to anything the photophone might have been able to achieve.
Still, it is interesting to speculate what might have happened if American Bell Telephone and its successor, AT&T, had had a research facility like Bell Labs to pursue intriguing scientific ideas with no immediate commercial potential. What if optical communication had been an area of active research for the entire twentieth century? Perhaps it would have petered out in America as it did in Europe; after all, the post-World War II communications revolution depended on scientific and technological developments that came half a century or more after Bell’s invention. Yet as today’s engineers make great strides with fiber optics and even light-based computers, one can only wonder how much more progress they might have made with a substantial body of knowledge about optical engineering already in place.