; --..- �-' f4�: . STRIKING PARALLELS between the telephones envisioned by electrode. In Bell's the variation would depend on the changes in the Elisha Gray and Alexander Graham Bell are evident in their respec­ area of the wedge-shaped needle tip immersed in the bath. The vary­ tive sketches of the instruments. Both Gray's transmitter(top) and ing current would then pass through an electromagnet(right) at the Bell's (bottom) depended on varying the resistance to the flow of cur­ receiving end of the circuit; variations in the magnetic field would rent from a battery. Both variations would be caused by the vertical cause a second diaphragm (in Gray's scheme) or a metal reed (in movement of a needle in a liquid bath; the motion would be due to Bell's) to vibrate, thereby reproducing the sound waves that actu­ the response of a diaphragm to the sound waves of the human voice. ated the transmitter. Gray made the sketch of his device on February In Gray's transmitter the variation in resistance would depend on 11, 1876, some two months after he conceived the idea. Bell made changes in the distance between the tip of the needle and the bottom his sketch on March 9, 24 days after filing his patent application. 156 © 1980 SCIENTIFIC AMERICAN, INC Two Paths to the Telephone As Alexander Graham Bell was developing the telephone Elisha Gray was doing the same. Bell got the patent, but the episode is nonetheless an instructive example of simultaneous invention by David A. Hounshell n one day in 1876-February 14-the one-third interest in the business, and also connected one lead of the second U.S. Patent Office received two Western Electric eventually became the circuit to the zinc bathtub and was clos­ I communications describing the sole supplier of telegraphic equipment ing the circuit and "taking shocks" from electrical transmission and reception of to Western Union. the induction coil by rubbing his hand, human speech by means of variations in Telegraphy had grown steadily in the which held the other lead, across the sur­ the resistance of the transmitter. The U.S. from its introduction in 1844, face of the tub. variable-resistance device was the origi­ and that growth had accelerated in the The vibrating reed made an audible nal telephone. The first description was Civil War years. By the end of the war hum, and when Gray's nephew rubbed in the form of a patent application by some 50,000 miles of telegraph wire had his hand on the tub, a second hum of the a 29-year-old amateur inventor whose been strung over routes totaling nearly same pitch was heard. Gray's interest name became world-famous: Alexander 30,000 miles, and a decade later the fig­ was piqued. He changed the frequency Graham Bell. The second description, ures had risen to 250,000 miles of wire of the reed and found that the sound which arrived only hours later, came over routes of more than 100,000 miles. made by the rubbing of his hand on the from a 41-year-old professional inven­ Until 1872, however, each wire could tub changed to match it. The action of tor who had been granted the first of his transmit only one message in one direc­ the induction coil was to transform the many electrical patents almost a decade tion at a time. Enlarging the transmis­ on-off impulses imposed on the circuit earlier: Elisha Gray. sion capacity between any two points by the vibrating reed into a sinusoidal Who was Elisha Gray? Why is Bell could be accomplished only by stringing wave of electric current. widely if not universally known as the new wires. Gray was quick to explore the phe­ inventor of the telephone and Gray, This one-way-at-a-time bottleneck nomenon of what he named vibratory who envisioned the same device at the was built into the telegraph. system be­ currents, seeking to find some practical same time, known to few except histori­ cause the transmitted signal consisted of use for their transmission and reception. ans of technology? To answer the ques­ intermittent pulses of direct current. In Although he found no immediate appli­ tion it is helpful to have an understand­ 1872, however, Western Union adopted cation, he so resolutely believed vibrato­ ing of not only the technical aspects of a "duplex" system of transmission de­ ry currents would have a major useful­ this classic example of simultaneous in­ veloped by Joseph B. Stearns, a Boston ness that he resigned as the superinten­ vention but also the social ones. In the electrician. A modification of the Morse dent of Western Electric, determined history of the telephone the differences system, the Stearns system allowed two to pursue the matter on an independent between the world of the professional messages to be transmitted simultane­ full-time basis. In order to do so he se­ and the world of the amateur appear at ously, one from each end of the wire. cured the financial backing of Samuel S. almost every turn, as will be made clear The adoption of the duplex system ef­ White, a wealthy manufacturer of den­ by a brief exploration of the two worlds, fectively doubled the capacity of the tistry equipment in Philadelphia. first Gray's and then Bell's. Western Union network. Could multi­ With funds at his disposal Gray soon Elisha Gray, born in Barnesville, plex systems be developed, systems that built four experimental devices: two Ohio, in 1835, attended Obedin College, would increase the capacity many times transmitters of frequencies in the audi­ but he was not graduated owing to ill further? One thing was certain: the in­ ble range and two receivers. One of health. His early interest in the electrical ventor of a multiplex system could vir­ the transmitters he called a single-tone aspects of telegraphy led in 1867 to his tually name his own price. transmitter; it was essentially a refine­ first patent, for a self-adjusting tele­ ment of his nephew's bathtub apparatus. graph relay. His device attracted the at­ ray's close relations with Western The other he called a two-tone trans­ tention of the principal firm in the field, G Union made him aware of the re­ mitter; it was capable of simultaneous­ the Western Union Telegraph Compa­ wards awaiting the successful inventor, ly generating sinusoidal waves of two ny. It also earned Gray enough mon­ and early in 1874 he hit on a solution different frequencies. One of the two re­ ey for him to secure a partnership in a almost by pure accident. One day he ceivers seems quaint in retrospect; the Cleveland firm that manufactured tele­ found his nephew, whom he allowed to other was quite conventional. graphic instruments. He and his partner, use his electrical apparatus, amusing The first receiver consisted of a violin Enos Barton, transformed the company himself in the bathroom with two bat­ with its strings removed and a silver into the nation's leading maker of elec­ tery-powered circuits. In one circuit the plate attached to the soundboard. When trical apparatus, renamed it the Western battery caused a reed "electrotome" one of the leads of the induction-coil Electric Manufacturing Company and to vibrate. The vibrations opened and circuit was connected to the plate and in the early 1870's relocated it in Chica­ closed the other circuit, which included the hand holding the other lead was go. In 1872 Western Union acquired a an induction coil. Gray's nephew had rubbed across the metal surface, as it 157 © 1980 SCIENTIFIC AMERICAN, INC was in the bathtub experiment, the tones Could not each tone be made to carry Within a few weeks of the bathtub ep­ generated by either transmitter were re­ a telegraph signal? The musical tele­ isode Gray, in a rush of experimental produced with a richer quality. The oth­ graph could function as a multiplex-sig­ activity, had discovered and in his mind er receiver consisted of an electromag­ nal transmitter if a receiver could be de­ explored the seemingly boundless pos­ net and a metal diaphragm. When the vised that was able to segregate the indi­ sibilities of utilizing audible vibratory magnet caused the diaphragm to vibrate vidual tones of the composite current. currents. In May of 1874, confident that' according to the frequencies of the cur­ For this purpose, Gray realized, neither he had sufficiently investigated the im­ rent in the induction-coil circuit, the of his receivers would be of any use. plications of these currents, he demon­ tones of the transmitters were faithful­ The magnet-and-diaphragm receiver, strated his transmitters and receivers ly reproduced. The results suggested to however, was perfectly suited to the to audiences of telegraphy experts in Gray three possible applications. third application Gray had in mind. If Washington, New York and Boston. Re­ The most obvious application and many combinations of tones could be ports of the demonstrations allow the probably the easiest to perfect was what carried by wire and the composite signal inference that he mentioned all three today would be called an electric organ; could then be reproduced electrically, potential applications of this work: the Gray thought of it as a "musical tele­ would it not be possible to transmit the transmission of music, the transmission graph." He would merely have to build sounds of the human voice? Gray may of multiple messages and the transmis­ a keyboard consisting of switches that have perceived an irony in this applica­ sion of the human voice.