The product of Edison's brain may be divided into three classes. The first embraces such arts and industries, or such apparatus, as have already been treated. The second includes devices like the tasimeter, phonomotor, odoroscope, etc., and others now to be noted. The third embraces a number of projected inventions, partially completed investigations, inventions in use but not patented, and a great many caveats filed in the Patent Office at various times during the last forty years for the purpose of protecting his ideas pending their contemplated realization in practice. These caveats served their purpose thoroughly in many instances, but there have remained a great variety of projects upon which no definite action was ever taken. One ought to add the contents of an unfinished piece of extraordinary fiction based wholly on new inventions and devices utterly unknown to mankind. Some day the novel may be finished, but Edison has no inclination to go back to it, and says he cannot under- stand how any man is able to make a speech or write a book, for he simply can't do it.
After what has been said in previous chapters, it will not seem so strange that Edison should have hundreds of dormant inventions on his hands. There are human limitations even for such a tireless worker as he is. While the preparation of data for this chapter was going on, one of the writers in discussing with him the vast array of unexploited things said: "Don't you feel a sense of regret in being obliged to leave so many things uncompleted?" To which he replied: "What's the use? One lifetime is too short, and I am busy every day improving essential parts of my established industries." It must suffice to speak briefly of a few leading inventions that have been worked out, and to dismiss with scant mention all the rest, taking just a few items, as typical and suggestive, especially when Edison can himself be quoted as to them. Incidentally it may be noted that things, not words, are referred to; for Edison, in addition to inventing the apparatus, has often had to coin the word to describe it. A large number of the words and phrases in modern electrical parlance owe their origin to him. Even the "call-word" of the telephone, "Hello!" sent tingling over the wire a few million times daily was taken from Menlo Park by men installing telephones in different parts of the world, men who had just learned it at the laboratory, and thus made it a universal sesame for telephonic conversation.
It is hard to determine where to begin with Edison's miscellaneous inventions, but perhaps telegraphy has the "right of line," and Edison's work in that field puts him abreast of the latest wireless developments that fill the world with wonder. "I perfected a system of train telegraphy between stations and trains in motion whereby messages could be sent from the moving train to the central office; and this was the forerunner of wireless telegraphy. This system was used for a number of years on the Lehigh Valley Railroad on their construction trains. The electric wave passed from a piece of metal on top of the car across the air to the telegraph wires; and then proceeded to the despatcher's office. In my first experiments with this system I tried it on the Staten Island Railroad, and employed an operator named King to do the experimenting. He reported results every day, and received instructions by mail; but for some reason he could send messages all right when the train went in one direction, but could not make it go in the contrary direction. I made suggestions of every kind to get around this phenomenon. Finally I telegraphed King to find out if he had any suggestions himself; and I received a reply that the only way he could propose to get around the difficulty was to put the island on a pivot so it could be turned around! I found the trouble finally, and the practical introduction on the Lehigh Valley road was the result. The system was sold to a very wealthy man, and he would never sell any rights or answer letters. He became a spiritualist subsequently, which probably explains it." It is interesting to note that Edison became greatly interested in the later developments by Marconi, and is an admiring friend and adviser of that well-known inventor.
The earlier experiments with wireless telegraphy at Menlo Park were made at a time when Edison was greatly occupied with his electric-light interests, and it was not until the beginning of 1886 that he was able to spare the time to make a public demonstration of the system as applied to moving trains. Ezra T. Gilliland, of Boston, had become associated with him in his experiments, and they took out several joint patents subsequently. The first practical use of the system took place on a thirteen-mile stretch of the Staten Island Railroad with the results mentioned by Edison above.
A little later, Edison and Gilliland joined forces with Lucius J. Phelps, another investigator, who had been experimenting along the same lines and had taken out several patents. The various interests were combined in a corporation under whose auspices the system was installed on the Lehigh Valley Railroad, where it was used for several years. The official demonstration trip on this road took place on October 6, 1887, on a six-car train running to Easton, Pennsylvania, a distance of fifty-four miles. A great many telegrams were sent and received while the train was at full speed, including a despatch to the "cable king," John Pender. London, England, and a reply from him.
 Broadly described in outline, the system consisted of an induction circuit obtained by laying strips of tin along the top or roof of a railway car, and the installation of a special telegraph line running parallel with the track and strung on poles of only medium height. The train and also each signalling station were equipped with regulation telegraphic apparatus, such as battery, key, relay, and sounder, together with induction-coil and condenser. In addition, there was a transmitting device in the shape of a musical reed, or buzzer. In practice, this buzzer was continuously operated at high speed by a battery. Its vibrations were broken by means of a key into long and short periods, representing Morse characters, which were transmitted inductively from the train circuit to the pole line, or vice versa, and received by the operator at the other end through a high-resistance telephone receiver inserted in the secondary circuit of the induction-coil.
Although the space between the cars and the pole line was probably not more than about fifty feet, it is interesting to note that in Edison's early experiments at Menlo Park he succeeded in transmitting messages through the air at a distance of 580 feet. Speaking of this and of his other experiments with induction telegraphy by means of kites, communicating from one to the other and thus from the kites to instruments on the earth, Edison said recently: "We only transmitted about two and one-half miles through the kites. What has always puzzled me since is that I did not think of using the results of my experiments on `etheric force' that I made in 1875. I have never been able to understand how I came to overlook them. If I had made use of my own work I should have had long-distance wireless telegraphy."
In one of the appendices to this book is given a brief technical account of Edison's investigations of the phenomena which lie at the root of modern wireless or "space" telegraphy, and the attention of the reader is directed particularly to the description and quotations there from the famous note-books of Edison's experiments in regard to what he called "etheric force." It will be seen that as early as 1875 Edison detected and studied certain phenomena--i.e., the production of electrical effects in non-closed circuits, which for a time made him think he was on the trail of a new force, as there was no plausible explanation for them by the then known laws of electricity and magnetism. Later came the magnificent work of Hertz identifying the phenomena as "electromagnetic waves" in the ether, and developing a new world of theory and science based upon them and their production by disruptive discharges.
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