Bell's first mental model for a speaking telegraph came from a variation on this reed mechanical representation, and also from experiments he had conducted with piano strings. In the summer of 1874, he put reeds on either pole of a horseshoe magnet, and experimented with sending the sound of either reed, separately or in combination. Bell's goal was to magnetize the reed itself and therefore avoid distortions that occurred when he used an unmagnetized reed in combination with an electromagnet--exactly the sorts of distortions that Gray was able to avoid through clever use of dampers and electromagnets of different resistances.
Bell's horseshoe magnet experiment was partly successful, enough to lead him to imagine a device he called the 'harp apparatus' with perhaps dozens of reeds on each pole of an electromagnet (see Figure 12). Such a device might function like the strings on a piano and vibrate in response to any tone made near them; these vibrations would then induce a current which could be carried to a receiving harp.
This harp was never built, and it was not fully described even in the sketch shown in Figure 12; instead, it served as a mental model--incomplete and unstable, because Bell had no idea how many reeds it would take to make it work, and he was sure it would not induce enough current to transmit a signal strong enough to be heard.
Figure 12: Bell's harp apparatus. One would speak against the reeds H, attached to a permanent magnet M; the vibration of the reeds would induce a curret in the electromagnet E which would be transmitted to E', cusing the reeds H' to reproduce the sound. This device was never built; Bell was not even sure how many reeds would be necessary (from Rhodes, 1929, p. 11).
In June of 1875, Bell and his new assistant Thomas Watson were working on the problem of multiple telegraphy. Bell had obtained support from Gardiner Hubbard, father of one of his pupils, Mabel. Hubbard wanted to break Western Union's virtual monopoly on what we would now call information services. He proposed a plan that would put such services in the post office, under contract to a corporation that Hubbard himself would found and head. When the Congress did not pass his scheme, Hubbard looked for other ways of ending Western Union's dominance (Carlson, 1994). One way was through the development of new technologies like the multiple harmonic telegraph system proposed by his daughter's teacher.
To complicate matters, Bell was courting Mabel. Therefore, out of deference to Gardiner Hubbard, telephonic researches had to take a back seat to telegraphy. On May 2nd, 1875, Bell wrote to "Papa and Mama: I think that the transmission of the human voice is much more nearly at hand than I had supposed. However this is kept in the background just now--as every effort is made to complete the Autograph arrangement so as to have it used on some line." The autograph was a device that would sent printed or written letters over a wire, and Bell had just obtained an important patent for this kind of technology, barely beating Elisha Gray.
There may also be a cognitive reason why Bell kept the speaking telegraph in the background, at least for a bit. When a scientist or inventor is pursuing a network of related enterprises, she or he may suspend a goal when confronted with an obstacle, and pursue other, related goals until a solution to the first goal emerges. The problem with the harp apparatus was that it required to many reads and the induced current would not be sufficiently strong to transmit speech. So Bell suspended the goal of speaking telegraphy, hoping a solution would emerge.
This is the beauty of a network of related pursuits--in the course of pursuing telegraphy, Bell found the solution to telephony. On June 2, 1875, Bell had set up three multiple telegraph stations, A, B and C, each with three of his tuned reed mechanical representations. He wanted to be able to pluck the first reed in A and have the first reeds in B & C vibrate. When Bell depressed the telegraph key corresponding to first reed at A, the corresponding reed at B vibrated well, but Watson, who was in another room with C, noticed it was stuck. To release it, Watson plucked it; Bell noticed that this caused the corresponding reed at B to vibrate powerfully. Bell then listened to each of the reeds at B in succession, placing his ear right against them, and heard both the pitch and the overtones of the tuned reed.
Seen from the standpoint of multiple telegraphy, this result was an error--one stuck reed caused three reeds at the other station to vibrate, and one could hear the overtones of each reed, whereas what one really wanted was to hear a single, pure tone. But given Bell's harp mental model, this error suggested a route to the transmission of speech. "These experiments at once removed the doubt that had been in my mind since the summer of 1874, that magneto-electric currents generated by the vibration of an armature in front of an electro-magnet would be too feeble to produce audible effects that could be practically utilized for the purposes of multiple telegraphy and of speech-transmission" (Bell, 1908, p. 59).
Bell immediately asked Watson to build a working telephone in which a reed relay was attached to a diaphragm or membrane with a speaking cavity over it. As one spoke into the cavity, the membrane would vibrate; these vibrations would be translated into an electrical current by the dampened reed, which would send them to a similar device on the other end. Unfortunately, this device did not produce intelligible speech, though Bell and Watson heard a kind of mumbling that suggested they were on the right track. Bell then wrote an application for a patent that included the transmission of speech; he used his reed relays to illustrate how this was to be done. The patent was submitted on February 14th, 1876.
Edison's famous patent for a carbon filament light also may have benefited from a lot of serendipity. By October of 1879, Edison had succeeded in creating a vacuum to one-millionth of an atmosphere in a bulb, had perfected a generator for the lighting system and was experimenting with platinum filaments (Friedel, 1985). The platinum was not entirely satisfactory. Legend has it that Edison was rolling a piece of compressed lambpack between his fingers one night when it occurred to him to put it in his new high vacuum bulb. Previous work had suggested carbon would simply burn up in a lamp, but in the high vacuum, it showed promise.
By June 2nd, 1875, Bell knew most of what he needed to know to create a telephone, but he believed that a single reed could not transmit with sufficient volume. Similarly, most of the pieces of Edison's incandescent lighting system were in place by October of 1877, but he believed that platinum was superior to carbon as a filament. When both inventors encountered results that suggested they were wrong, they were primed to take advantage of them, and went to patent shortly afterwards. In the case of Edison's team, it took several weeks of careful experimenting before they were ready, but even so, it is unlikely that they had a working lamp when they submitted their patent: "The patent application submitted November 4 did not so much describe what had actually been made at Menlo Park as what Edison and his colleagues knew should be made" (Friedel, 1985, p. 106).
This page was last edited: Wednesday, July 14, 1999