After his caveat, Elisha Gray all but abandoned speaking telegraphy until June, after a major Centennial exhibition in Philadelphia, when he heard the human voice through one of Bell's telephones. Had Bell used a liquid transmitter on this occasion, Gray's surprise might have turned to suspicion. But despite his early success with the liquid transmitter, at the Centennial Bell demonstrated magnetic induction designs that looked more like the ones in his first patent. Improvements on this magneto design formed the basis of his second speaking telegraph patent, in 1877 . Why did Bell abandon the approach that led to the first transmission of speech?
Finn tested the Bell apparatus housed at the Smithsonian and concluded that, "Bell apparently abandoned the variable-resistance transmitter in favor of the magneto transmitter for the simple reason that the latter worked better and with greater consistency than the variable-resistance liquid transmitter he had designed, and this decision came after an impressively large number of experiments. My recent experiments confirm the validity of Bell's judgment." (Finn, 1966, p. 15)
Finn tested Bell's devices with an oscilloscope; Bell used his ear, and compared current results with what he had written about previous ones in his notebooks. Therefore, a fairer judge of Bell's successes may be his notebook record, which suggests that he continued to obtain positive results with the liquid transmitter long after March 10th, results at least as positive as any he had achieved with magneto designs.
Another possibility was that Bell wanted to keep his liquid experiments a secret, knowing that Gray was working on something similar. This implies some clever guesswork on Bell's part, or a spy at the patent office. All Bell ever admitted knowing was that his patent and Gray's caveat were in conflict over the matter of variable resistance.
There is a third possibility: that Bell saw the liquid transmitter primarily as a way of testing his mental model for the transmission of speech, not as a practical device. The liquid would need to be kept at just the right level. One can imagine running to 'top off the transmitter' every time the phone rang! Bell probably never seriously considered a practical liquid transmitter.
But how could a liquid transmitter confirm Bell's mental model? Contacts vibrating in water do not correspond in form to the bones of the middle ear. But they did serve the same function: translating the sinusoidal patterns of speech into an undulating current. The form of the ossicles was fading into the background, but its function remained paramount.
It is well to remember Freud's point about human behavior being overdetermined. In truth, some combination of all the above motives might account for Bell's decision. It is worth taking a brief look at the experiments Bell conducted between March 10th and May.
Recall that on March 10th, Bell realized his liquid transmitter was functioning as a battery. To avoid this problem, Bell used platinum on both contacts. On March 13th, his future father-in-law and principal backer Gardiner Hubbard dropped by and listened to the transmitter; he "was convinced that articulate sounds were transmitted along the wire--although the articulation was so muffled as to be to him unintelligible unless...he was informed beforehand of its sense" (Bell, 1876, p. 51). Bell concluded that "the experiments were on the whole satisfactory as demonstrating the fact that the timbre as well as the pitch of vocal sounds had been transmitted telegraphically" (Bell, 1876, p. 52). In other words, this experiment represented another confirmation of his undulating current mental model. Perhaps more importantly, this confirmation continued the process of converting Gardiner Hubbard to Bell's view of the potential benefits of the telephone.
After several frustrating efforts to improve transmission, on March 15th, Bell paused to reflect: "Instead of practical experiment I have come to the conclusion that I can best advance the subject by making a theoretical investigation of the effects produced upon a voltaic current by the vibration of the conducting wire in a liquid included in the circuit--and deducing thence the best way of increasing the amplitude of the electrical undulations so as to admit of the transmission of vocal utterance over long distances" (Bell, 1876 , p. 57).
In other words, Bell decided a search in what Klahr and Dunbar (Klahr, 1988) call the hypothesis space would be more profitable at this stage than further work in the experimental space, especially in light of his limited equipment and electrical skills. He sketched a series of thought experiments concerning the relationship between battery power, line resistance and resistance of the liquid, and sketched the shape of the undulations he thought might result from different combinations of these factors. Eventually an article in a handbook convinced him that even acidulated water would be over a million times more resistant than copper wire and would be far too great for the batteries he was using. The key to a liquid transmitter was to lower water resistance--either by acidulating the water, or bringing the contacts closer together, or both.
Bell carefully experimented with these options, and found if he separated the contacts by a thin film of water, the reed of the receiver often got stuck against the electromagnet. This led him to focus on the distance of the receiving reed from the coil, and on March 27th, to an experiment in which he used his two favorite forms of magneto receiver in a circuit. This represented his first experiment with an all-magneto design since March 8th. He obtained a positive result. Bell soon was back to experimenting with liquid devices, partly because they offered a solution to the problem of autograph telegraphy: sending letters over the wire. Bell's autograph telegraph experiments were part of his network of enterprises.
One particular experiment on April 5th, involving a transmitter in which a carbon contact dipped into mercury, allowed Bell to hear the difference between undulating and intermittent currents repeatedly and clearly, leading him to conclude "that my theory is correct--that musical notes which conflict with one another when transmitted by means of an intermittent (current) will not interfere with one another when the undulatory current is employed." (Bell, 1876b, p. 97--emphasis his). Another experimenter might have referred to this result as an error: the intermittent current kept interfering with the undulatory because the pencil was too short to be adjusted as precisely as necessary. But Bell had a knack for converting errors into positive results--in this case a positive result that also confirmed his theory.
On May 5th, Bell returned to magneto devices; from this point forward, the liquid transmitter virtually disappears from his notebook. He was preparing for a May 10, 1876, presentation to the American Academy of Arts and Sciences; the pressure of a deadline forced Bell to confirm that a magneto device could serve as both transmitter and receiver. In the talk, he placed much greater emphasis on his work with magneto devices, despite the fact that his notebooks suggested their performance was not consistently superior to that of liquid variable resistance devices: he could get either type to produce vowels, musical tones and even occasional phrases, but neither would permit consistent discrimination of consonants. On May 25th an audience at MIT heard occasional sentences transmitted from a neighboring house over a magneto telephone. "Vowels are faithfully reproduced; consonants are unrecognizable" reported the Boston Transcript (Bruce, 1973, p. 189).
Bell's exhibit at the. Philadelphia Centennial was hastily added to the program by Gardiner Hubbard, who played such a key role in putting Bell's work forward. One of the reasons I admire Bell is because he was a busy, overworked teacher like me, buried under papers he had to grade. He didn't want to take time from his teaching to go to the Centennial; his fiancee Mabel took him to the station and all but shoved him on the train.
Elisha Gray, in contrast, had an elaborate, carefully choreographed set of demonstrations ready, supported by Western Union. On June 25, the judges, accompanied by Dom Pedro, the Emperor of Brazil, listened to a long lecture by Gray and watched him demonstrate both musical and multiple telegraphy, but not speaking telegraphy.
The clever Hubbard had put Bell in the same hotel with three of the judges, so by the time they saw Gray's exhibit, they had already heard Bell's account of the scientific principles underlying his speaking telegraph. The judges then trudged off to see Bell's exhibit. It included multiple harmonic telegraph equipment, but also Bell's latest speaking telegraph--a magneto design that included a new receiver, which he had created by scavenging parts in Charles Williams' shop. Bell had found an iron cylinder with a rod running up the middle; when wire was wrapped around the rod, the whole apparatus became an electromagnet, with one pole represented by the pole of the cylinder and the other pole by the top of the rod. Bell added a lid of sheet iron, which vibrated in response to the undulating current from the transmitter.
Wires from this receiver ran to the corresponding transmitter in another part of the exhibit hall. Bell sang and shouted into this transmitter while Sir William Thomson, one of the judges, listened at the receiving end. He heard the words, "Do you understand what I say?", and shouted, "I must see Mr. Bell!" Thomson ran to find Bell, reported the success, and went back to hear more. Dom Pedro was next, heard part of Hamlet's soliloquy, and also rushed off to congratulate Bell. Even Elisha Gray heard "Aye, there's the rub" faintly when he took his turn at the receiver (Bruce, 1973, p. 197). Bell's use of a familiar passage was a clever way of insuring that listeners could fill in the gaps in the faint and unsteady transmission.
The delighted and surprised reaction of his listeners would be echoed time and time again when Bell, Watson and others took their invention 'on the road' and did live demonstrations. For a professional telegrapher like Gray, this invention had always been subsidiary to the telegraph. As he said in a letter to his attorney, A.L. Hayes in October of 1875:
Bell seems to be spending all his energies on [sic] talking telegraph. While this is very interesting scientifically it has no commercial value at present, for they can do much more business over a line by methods already in use than by that system. I don't want at present to spend my time and money for that which will bring no return.
He also publicly conceded all priority in matters related to speaking telegraphy in a letter to Bell on March 5th, 1877, in which he said,
Of course you had no means of knowing what I had done in the matter of transmitting vocal sounds. When, however, you see the specification, you will see that the fundamental principles are contained therein. I do not, however, claim even the credit of inventing it, as I do not believe a mere description of an idea that has never been reduced to practice, --in the strict sense of that phrase,--should be dignified with the name invention
In later years Gray regretted this concession, especially given the fact that Bell got a patent without achieving a reduction to practice. But Gray also had to admit that Bell was the first to achieve spoken transmission, and that his electromagnetic induction design was original: "I thought it would be impossible to make a practical working speaking telephone on the principle shown by Professor Bell, to wit: generating electric currents with the power of the voice, as it seemed to me then that the vibrations were so slight in amplitude and the inductor necessarily so light that the currents thus generated would be too feeble for practical purposes." (1880, Part I, 142-3) Eventually, Gray designed and patented several magneto speaking telegraphs of his own, in an effort to circumvent Bell's patent. He also built and tested his liquid transmitter after the Centennial, and applied for patents in which it would be used in combination with various receivers. Again, Gray relied on a patent-combinations heuristic, using familiar mechanical representations like the washbasin-electromagnet design as both transmitter and receiver in combination with other mechanical representations, including the liquid transmitter featured in his caveat (Gorman, Mehalik, Carlson, & Oblon, 1993).
Bell did not even bother to demonstrate his liquid transmitter at the Centennial, and liquid designs virtually disappear from his notebook. The success of the liquid transmitter may have disconfirmed Bell's idea that the form of the armature ought to be modeled on the ossicles. On September 27th, Bell wondered if he should "try to use the membrane of the human ear as a transmitter. Attach light piece of iron or steel to maleus--having removed stapes and incus." (Bell, 1876, Vol II, p. 83) In this extraordinary passage, Bell reminds us that the ear still serves as a mental model. Attaching an armature to the maleus is similar to his ear phonautograph, in which a brush was attached to all three bones of the middle ear. By removing the stapes and the incus, Bell has removed the hinge that he thought was essential in his February 21st sketch of the ear mental model. The form of the ossicles was gradually disappearing.
His first production telephones substituted a heavy metal diaphragm for the hinged armature suggested by the ossicles analogy, but otherwise they were identical to devices used in his first patent. His discovery of the benefits of a metal diaphragm involves the way in which he used his notebooks as a tool for reflection. On July 11, 1876, Bell tried attaching a disk of tagger's iron to the membrane of the transmitter, replacing the metal strip he usually used. He found sounds were louder with the disk than with the strip. He experimented with a circuit of 19660 ohms resistance and ten battery cells, and found that "the softer the initial articulation the more distinct was the utterance at the other end of the line" (Bell, 1876, Vol II, p. 28). Bell was at this point working to achieve long-distance transmission, and in this sequence of experiments, he occasionally used water to simulate the high resistance of a long-distance line.
The iron disk disappeared as Bell went into a long sequence of multiple telegraph experiments, followed by experiments using springs on the membrane, which led to his insight on September 27th that the spring need not be modeled after the form of the ossicles. Then on October 2nd, he re-read his notebook and noticed the July 11th experiment with the iron disk. He could not imagine why they hand not tried this again. He and Watson glued a steel disk to the membrane. "The articulation was much more distinct" (Bell, 1876, Vol II, p. 3). On October 7th, the two men carried on an enthusiastic telephone conversation, in which Watson said, "Success has at last [attended] our efforts" (Bell, 1876, Vol III, p. 4). The fact that Bell could not make out the word 'attended' scarcely dampened their enthusiasm. Long conversations followed, and were recorded in the notebook.
In January, 1877, Bell submitted a second patent that emphasized speaking telegraphy. The membrane was now gone altogether; in its place was a heavy plate of iron or steel, whose position with respect to an electromagnet or permanent magnet could be adjusted to produce the best transmission or reception. Bell and Watson's first production telephones were built along these lines, but were quickly superseded by better transmitters using carbon as a medium of variable resistance. Bell and Watson also put together an effective 'road show' in which Bell would place a receiver in front of an audience and Watson would sing to them from a remote location (Bruce, 1973). Just as at the Centennial, these shows had a magical effect on audiences. Never mind that much of the effect depended on the way Watson bellowed into the transmitter. Bell's telephone transmitter was quickly superseded by better devices (Carlson, 1989), but he had recognized the importance of transmitting speech and played a major role in creating a market for this new technology.
Invention involves more than creating a device; to borrow the sociologist John Law's felicitous phrase, it is an exercise in heterogeneous engineering (Law, 1987). What Law means is that successful inventors build a network of technologies, patents, backers, buyers--even, in Bell's case, scientists. Bell did not build this network all by himself; instead, he recruited allies like Gardiner Hubbard, Sir William Thomson and others who promoted his invention. It was Hubbard who created the Bell Corporation and made his son-in-law a millionaire. Gray, meanwhile, successfully developed an improved form of duplex and used it over long-distance lines starting in May of 1877. He referred to this duplex as a telephone, in the spirit of Philip Reis' original invention, but what Gray had in mind was a harmonic telegraph. He could send two messages at the same time over a long-distance line in a way that did not interfere with all the local Morse telegraph messages that were being sent over the same wires at the same time (Gray, 1977). This was a major accomplishment. But the entire technological front had been transformed by Bell's invention, and conquering the old reverse salient was now a minor victory.
This page was last edited: Wednesday, July 14, 1999