Edison continued his telephone work through a number of years and made and tested many other kinds of telephones, such as the water telephone, electrostatic telephone, condenser telephone, chemical telephone, various magneto telephones, inertia telephone, mercury telephone, voltaic pile telephone, musical transmitter, and the electromotograph.
The principle of the electromotograph was utilized by him in more ways than one; first of all in telegraphy. Soon after the time he had concluded the telephone arrangement just mentioned a patent was issued to a Mr. Page. This patent was considered very important. It related to the use of a retractile spring to withdraw the armature lever from the magnet of a telegraph or other relay or sounder, and thus controlled the art of telegraphy, except in simple circuits.
"There was no known way," remarks Edison, "whereby this patent could be evaded, and its possessor would eventually control the use of what is known as the relay and sounder, and this was vital to telegraphy. Gould was pounding the Western Union on the Stock Exchange, disturbing its railroad contracts, and, being advised by his lawyers that this patent was of great value, bought it. The moment Mr. Orton heard this he sent for me and explained the situation, and wanted me to go to work immediately and see if I couldn't evade it or discover some other means that could be used in case Gould sustained the patent. It seemed a pretty hard job, because there was no known means of moving a lever at the other end of a telegraph wire except by the use of a magnet. I said I would go at it that night. In experimenting some years previously I had discovered a very peculiar phenomenon, and that was that if a piece of metal connected to a battery was rubbed over a moistened piece of chalk resting on a metal connected to the other pole, when the current passed the friction was greatly diminished. When the current was reversed the friction was greatly increased over what it was when no current was passing. Remembering this, I substituted a piece of chalk, rotated by a small electric motor for the magnet, and connecting a sounder to a metallic finger resting on the chalk, the combination claim of Page was made worthless. A hitherto unknown means was introduced in the electric art. Two or three of the devices were made and tested by the company's expert. Mr. Orton, after he had had me sign the patent application and got it in the Patent Office, wanted to settle for it at once. He asked my price. Again I said, 'Make me an offer.' Again he named one hundred thousand dollars. I accepted, providing he would pay it at the rate of six thousand dollars a year for seventeen years. This was done, and thus, with the telephone money, I received twelve thousand dollars yearly for that period from the Western Union Telegraph Company."
A year or two later the electromotograph principle was again made use of in a curious manner. The telephone was being developed in England, and Edison had made arrangements with Colonel Gouraud, his old associate in the automatic telegraph, to represent his interests.
A company was formed, a large number of instruments were made and sent to London, and prospects were bright. Then there came a threat of litigation from the owners of the Bell patent, and Gouraud found he could not push the enterprise unless he could avoid using what was asserted to be an infringement of the Bell receiver.
He cabled for help to Edison, who sent back word telling him to hold the fort. "I had recourse again," says Edison, "to the phenomenon discovered by me some years previous, that the friction of a rubbing electrode passing over a moist chalk surface was varied by electricity. I devised a telephone receiver which was afterward known as the 'loud-speaking telephone,' or 'chalk receiver.' There was no magnet, simply a diaphragm and a cylinder of compressed chalk about the size of a thimble. A thin spring connected to the center of the diaphragm extended outwardly and rested on the chalk cylinder, and was pressed against it with a pressure equal to that which would be due to a weight of about six pounds. The chalk was rotated by hand. The volume of sound was very great. A person talking into the carbon transmitter in New York had his voice so amplified that he could be heard one thousand feet away in an open field at Menlo Park. This great excess of power was due to the fact that the latter came from the person turning the handle. The voice, instead of furnishing all the power, as with the present receiver, merely controlled the power, just as an engineer working a valve would control a powerful engine.
"I made six of these receivers and sent them in charge of an expert on the first steamer. They were welcomed and tested, and shortly afterward I shipped a hundred more. At the same time I was ordered to send twenty young men, after teaching them to become expert. I set up an exchange of ten instruments around the laboratory. I would then go out and get each one out of order in every conceivable way, cutting the wires of one, short-circuiting another, destroying the adjustment of a third, putting dirt between the electrodes of a fourth, and so on. A man would be sent to each to find out the trouble. When he could find the trouble ten consecutive times, using five minutes each, he was sent to London. About sixty men were sifted to get twenty. Before all had arrived, the Bell Company there, seeing we could not be stopped, entered into negotiations for consolidation. One day I received a cable from Gouraud offering 'thirty thousand' for my interest. I cabled back I would accept. When the draft came I was astonished to find it was for thirty thousand pounds. I had thought it was dollars."
After the consolidation of the Bell and Edison interests in England the chalk receiver was finally abandoned in favor of the Bell receiver—the latter being more simple and cheaper. Extensive litigation with newcomers into the telephone field followed, and Edison's carbon transmitter patent was sustained by the English courts, while Bell's was declared invalid.
In America, the competition between the Western Union and Bell companies, which had been keen and strenuous, was finally brought to an end under an agreement, the former company agreeing to retire from the telephonic field and the latter company agreeing to stay out of the telegraphic field. Through its ownership of Edison's carbon transmitter invention, the Western Union company came to enjoy an annual income of several hundred thousand dollars for some years as a compensation for its retirement from telephony under this agreement.
The principle involved in Edison's carbon-transmitter gave birth to another interesting device called the microphone, by means of which the faintest sounds could be very plainly heard. For instance, the footsteps of a common house-fly make a loud noise when the hearing is assisted by the microphone. As every one knows, the microphone is universally used in our modern radio.