Background Information

Alexander Graham Bell is the man usually given credit for the invention of the telephone. Certainly, the courts awarded him one of the most valuable patents in American history, a patent that made him a millionaire and became the foundation for one of America's largest corporations. But at the time of his invention, Bell's claim was hotly disputed by a number of inventors, leading to years of arguments in the courts.

One of these inventors was Elisha Gray, an accomplished electrician who possessed a number of important telegraph patents and who had come into conflict with Bell in the area of harmonic multiple telegraphy. The telephone looks to us now like an 'obvious' invention. But in fact the cutting-edge technology of the day was the multiple telegraph. By 1876, two messages could be sent over a single wire; the inventor who could send 8 or16 would have his fortune made. Imagine stock quotes--if you used a telephone, a broker would have to read them to you one-by-one; if you used a telegraph, you could send 16 or more at the same time.

One way of accomplishing multiple telegraphy would be to send and de-code separate tones--perhaps, as Bell envisioned, by the use of multiple tuning forks, or as Gray envisioned, by a transmitter that resembled an organ [2]. Imagine a set of 8 tuning forks, each with a distinct tone. You could send 8 stock quotes by putting one with each of the forks, and sending the dots and dashes by cutting the fork in and out of a long-distance circuit. A telegraph operator on the other end would listen for each of the separate tones, and record the message. This promising new technology was calledharmonic multiple telegraphy because it depended on musical tones. Businesses thought of telegraphy as the wave of the future, and what we now call telephony as a minor application.

Bell wasn't so sure, even though his father-in-law, Gardiner Hubbard, was pushing him to develop a multiple telegraph and his father, Alexander Melville, was pushing him to develop a device like a fax machine that would send letters. Bell was in many ways a 'gifted student'--the year before he went to high school, he and a friend liked to play around a local mill. The friend's father was the mill-owner; partly out of exasperation, he challenged the boys to 'do something useful'. When asked what that might be, he picked up a few grains and asked them if they could invent a way to take the husks off wheat. They succeeded in putting together a device that had rotating paddles with brushes on them, which the surprised mill owner actually used for a time. Bell's father also kept him and his brothers engaged in scientific experiments, like building an operating model of the human vocal chords and mouth that they used to say 'Ma-ma" so convincingly that they fooled a neighbor into searching for the baby!

Bell's father was a teacher of the deaf, and he imparted this knowledge to his only surviving son--Bell's brothers died of tuberculosis. Bell was the only telegraph inventor who understood how much we communicate via speech. He tried to build devices that would allow the deaf to see the pattern of speech sounds they were making and compare them with a kind of template. One of these devices was built around an actual human ear, which gave Bell an intimate understanding of how sounds are turned into waves by the bones of the middle ear.

These experiments led Bell to propose that the way to create a 'speaking telegraph' was to 'follow the analogy of nature'. Inventors often adopt this strategy: if nature has solved a problem, why not imitate nature? Bell, with help from his assistant Watson, built a kind of electromechanical ear in 1875, in which one spoke into a tube that ended in a membrane like the eardrum; a piece of metal was glued to the membrane and attached with a hinge to an electromagnet, which amplified the vibrations much like the bones of the middle ear [3]. This first telephone came about as a result of an accident. Watson had been trying to transmit telegraph signals; when one of the metal reeds got stuck, he plucked it in an effort to break it free. Bell came rushing into the room to find out what Watson was doing, because he had heard a strong signal in the other room from the receiving reed, strong enough so that he knew he could use this simple device to transmit speech. Like many other inventors, Bell took advantage of accidents and mistakes that would have been ignored by someone else.

On February 14, 1876, Bell's father-in-law submitted Bell's patent for "Improvement in Telegraphy"; this application was a bold attempt to patent the kind of current one would have to use to send either speech or musical tones over a wire (see Exhibit 1, 'The First Bell Patent".) Bell felt the key to voice transmission was an 'undulatory' current, which would take the sinusoidal sound wave and translate it into a series of corresponding electrical impulses that would have the same shape. In contrast, multiple telegraphy typically used an intermittent or on-off current. Bell sketched a simple system that he thought would transmit and receive such currents, using the reeds he had experimented with in 1875--even though at the time, he still had not been able to send speech over a wire. Bell was a bold gambler--he figured he could eventually make this device work; meanwhile, he had better patent something before someone else did.

It was a good thing he moved quickly--a few hours after his father-in-law submitted Bell's patent application, Elisha Gray applied for a caveat which outlined a device he though would transmit speech. (See Exhibit 2 for Gray's caveat.) Caveats are no longer used, but in the 19th-century, inventors filed them when they had an idea that they intended to patent eventually; the caveat gave them the right to be notified of any future patent applications for similar inventions. It was one way of hedging your bets: if you were pursuing several invention ideas, you could caveat one of them and set it aside, knowing that you would be notified if anyone else came along with a similar idea. After notification, you could still patent your idea and still have priority. In the patent system, you never want to be second! What this meant is that Gray could be vague about some details of his apparatus--he could, in effect, promise to iron them out later.

Gray's device was based on the 'lover's telegraph,' the old trick of connecting two cans via a string; if the proper tension is maintained, one can talk and listen without others hearing. Gray replaced the string with wire, then cut the wire and made part of it dip into water, which acted as a medium of high resistance. When one spoke into the mouthpiece, the diaphragm would vibrate, causing the needle to rise and fall. As the needle got closer to the bottom of the water, the current would increase; as it drew away, the current would decrease. Batteries maintained the current.

The lover's telegraph suggested that a complex sound such as the human voice could be transmitted through a single vibrating point on a diaphragm. Yet Gray spoke of using multiple diaphragms in the same way he had used multiple devices in his harmonic telegraph. Like Bell, Gray did not have a working device.

The device Bell first used to transmit speech on March 10, 1876, looks suspiciously similar to Gray's caveat. ( See Exhibit 3, a page from Bell's experimental notebook.) This naturally has led both lawyers and historians to charge that Bell somehow stole Gray's idea [4].

Let 's take a closer look at these devices. (To follow this discussion, you will have to look at the pictures in Exhibit 2 and Exhibit 3). First and most obviously, each inventor used a different receiver. Bell's system, on top in the figure, included his favorite telegraph receiver, a steel reed. Gray used a resonant globe reminiscent of his harmonic telegraph receivers. Clearly, neither inventor had to 'steal' the other's receiver, though both functioned similarly--the fluctuating current from the transmitter caused a magnetic field at the receiving end, which set either the resonant chamber or the reed into vibration.

Second, there are also differences in the transmitters. Gray thought the critical factor in changing the current was the distance between the wire and the contact at the bottom of the liquid. Gray's wire was therefore immersed very deeply in the water, and the contact with the rest of the circuit lies directly beneath it. To get this transmitter to work, one would have to adjust the distance between needle and contact very carefully.

Bell, in contrast, thought the critical factor was the relative areas of the two contacts that were immersed in the liquid [5]. The needle from his diaphragm lay close to the surface of the liquid, and the other contact was off to one side. In experiments before and after his first successful transmission, Bell varied the relative surface areas of his contacts. In one test, he replaced the vibrating contact with a bell, thereby maximizing the surface area in contact with the water. The bell didn't work. From this and other experiments Bell concluded that the sound from the receiver was loudest when the surface area of the side contact was largest and the vibrating surface in contact with the water was smallest. This conclusion is reflected in his successful liquid transmitter, which has a vibrating needle barely making contact with the water and a large brass pipe as the other contact. To get this transmitter to work effectively, the water has to form a little 'hill', or meniscus, around the needle.

Another difference in the transmitters is the devices that one speaks into. Gray shows an insulated cylinder of glass; Bell shows a speaking tube of the sort he used in earlier experiments. Finally, Gray thought he might use a series of these liquid transmitters; because he was only submitting a caveat, he could hedge his bet and not decide whether to use one or many until he had conducted further experiments. Bell, in contrast, was certain that he would need only one transmitter. To summarize, Bell's liquid transmitter and Gray's caveat device stem from different mental models; Bell did not simply copy Gray's transmitter, as some have suggested. [6]

In the end, Gray responded by giving Bell 'full credit for the talking feature of the telephone.' This emphasis on talking as a feature suggested the extent to which Gray regarded talking as only one relatively minor spin-off from a multiple telegraph [7]. Indeed, after this patent/caveat controversy, Bell continued to work on improving his telephone (see Exhibit 6, "The Second Bell Patent"), while Gray turned to perfecting his harmonic multiple telegraph. But when, much later, it became apparent that the future lay with telephony, Gray and Bell fought it out in court, with Bell declared the eventual winner--in part because he was a model witness who could describe his invention process in excruciating detail.
