How The Early Telephones Were Invented
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Science and Technology
Dec 6, 2007
spartanmalc
How The Early Telephones Were Invented
Today's cell phones are packed with advanced technology too intricate to easily understand. They represent the very pinnacle of personal technology and the science and craft of their designers is clearly evident. In this article, I want to show you just how far we have come in our technology by revisiting the early developers of the first telephones, and showing what technology they created. It has been shown that in order to transmit speech by electricity it is necessary to cause an undulatory or alternating current to flow in the circuit over which the transmission is to be effected, and that the strength of this current must at all times be directly proportional with the vibratory movements of the body producing the sound. Bell's magneto transmitter was used as the generator of this current; as a dynamo, in fact, the energy for driving which was derived from the sound waves set up by the voice. The amount of energy so derived was, however, necessarily very small and the current correspondingly weak, and for this reason this was not a practical form of transmitter, except for comparatively short lines. Elisha Gray devised a transmitter which, instead of generating the undulatory current itself, depended for its action on causing variation in the strength of a current generated by some separate source; this variation in current strength always being in accordance with the movements of the diaphragm. He mounted on his horizontal vibrating diaphragm a metal needle, extending into a fluid of low conductivity, such as water. The needle formed one terminal of the circuit, the other terminal being a metal pin, extending up through the bottom of the containing vessel. The vibration of the diaphragm was supposed to cause changes in the resistance of the path through the fluid on account of the varying distance between the points of the electrodes and therefore corresponding changes in the strength of the current. Bell also used a liquid transmitter in which a conducting liquid was held in a conducting vessel, forming one terminal of the circuit. The other terminal was a short metallic needle, carried on the diaphragm, and projecting slightly into the liquid, so that the area of contact between the liquid and the needle would be varied to better advantage by the vibration of the diaphragm than if the needle were immersed a greater distance into the fluid. Bell's liquid transmitter depended on variation in the extent of immersion of the electrode, while Gray's instrument, owing to the great extent to which the pin was immersed, depended rather on the variation in the length of the conducting path through the liquid itself, a faulty principle for this purpose. Bell's liquid transmitter was also exhibited at the Philadelphia Centennial in 1876, and, unlike that of Reis, simply caused variations in the resistance of the circuit, and thereby allowed a continuous but undulatory current to pass over the line, the variations in which were able to reproduce all the delicate shades of timbre, loudness, and pitch necessary in articulate speech. Gray and Bell embodied, or attempted to embody, in these instruments the main principle upon which all successful battery transmitters are based. A battery furnished the current, and the transmitter, actuated by the voice, served to modulate it. It was not long, however, before a much better means was devised for putting this principle into practice. In 1877 Emile Berliner, of Washington, D. C., filed a caveat, and later in the same year applied for a patent on a transmitter, depending upon a principle pointed out in articles published in 1856, 1864 and 1874 by the French scientist, Du Moncel, that if the pressure between two conducting bodies forming part of an electric circuit be increased,.the resistance of the path between them will be diminished, and conversely, if the pressure between them be decreased, a corresponding increase of resistance will result. As primitive as these devices may seem to us today, the underlying principles are sound and form the basis of all our modern sound transmtting devices, from PC microphones to the new Apple iPhone.
Malcolm Blake has a burning interest in all things related to telephones, both recent and in the past. Here are two of his more recent writings about Reverse Lookup Phone Sites and Reverse Number Search Directories.
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