Edison, His Life and Inventions [60]
at the same time. No one line of investigation has ever been enough to occupy his thoughts fully; or to express it otherwise, he has found rest in turning from one field of work to another, having absolutely no recreations or hobbies, and not needing them. It may also be said that, once entering it, Mr. Edison has never abandoned any field of work. He may change the line of attack; he may drop the subject for a time; but sooner or later the note-books or the Patent Office will bear testimony to the reminiscent outcropping of latent thought on the matter. His attention has shifted chronologically, and by process of evolution, from one problem to another, and some results are found to be final; but the interest of the man in the thing never dies out. No one sees more vividly than he the fact that in the interplay of the arts one industry shapes and helps another, and that no invention lives to itself alone.
The path to the quadruplex lay through work on the duplex, which, suggested first by Moses G. Farmer in 1852, had been elaborated by many ingenious inventors, notably in this country by Stearns, before Edison once again applied his mind to it. The different methods of such multiple transmission--namely, the simultaneous dispatch of the two communications in opposite directions over the same wire, or the dispatch of both at once in the same direction--gave plenty of play to ingenuity. Prescott's Elements of the Electric Telegraph, a standard work in its day, described "a method of simultaneous transmission invented by T. A. Edison, of New Jersey, in 1873," and says of it: "Its peculiarity consists in the fact that the signals are transmitted in one direction by reversing the polarity of a constant current, and in the opposite direction by increasing or decreasing the strength of the same current." Herein lay the germ of the Edison quadruplex. It is also noted that "In 1874 Edison invented a method of simultaneous transmission by induced currents, which has given very satisfactory results in experimental trials." Interest in the duplex as a field of invention dwindled, however, as the quadruplex loomed up, for while the one doubled the capacity of a circuit, the latter created three "phantom wires," and thus quadruplexed the working capacity of any line to which it was applied. As will have been gathered from the above, the principle embodied in the quadruplex is that of working over the line with two currents from each end that differ from each other in strength or nature, so that they will affect only instruments adapted to respond to just such currents and no others; and by so arranging the receiving apparatus as not to be affected by the currents transmitted from its own end of the line. Thus by combining instruments that respond only to variation in the strength of current from the distant station, with instruments that respond only to the change in the direction of current from the distant station, and by grouping a pair of these at each end of the line, the quadruplex is the result. Four sending and four receiving operators are kept busy at each end, or eight in all. Aside from other material advantages, it is estimated that at least from $15,000,000 to $20,000,000 has been saved by the Edison quadruplex merely in the cost of line construction in America.
The quadruplex has not as a rule the same working efficiency that four separate wires have. This is due to the fact that when one of the receiving operators is compelled to "break" the sending operator for any reason, the "break" causes the interruption of the work of eight operators, instead of two, as would be the case on a single wire. The working efficiency of the quadruplex, therefore, with the apparatus in good working condition, depends entirely upon the skill of the operators employed to operate it. But this does not reflect upon or diminish the ingenuity required for its invention. Speaking of the problem involved, Edison said some years later to Mr. Upton, his mathematical assistant, that "he always considered he was only working from one room to another.
The path to the quadruplex lay through work on the duplex, which, suggested first by Moses G. Farmer in 1852, had been elaborated by many ingenious inventors, notably in this country by Stearns, before Edison once again applied his mind to it. The different methods of such multiple transmission--namely, the simultaneous dispatch of the two communications in opposite directions over the same wire, or the dispatch of both at once in the same direction--gave plenty of play to ingenuity. Prescott's Elements of the Electric Telegraph, a standard work in its day, described "a method of simultaneous transmission invented by T. A. Edison, of New Jersey, in 1873," and says of it: "Its peculiarity consists in the fact that the signals are transmitted in one direction by reversing the polarity of a constant current, and in the opposite direction by increasing or decreasing the strength of the same current." Herein lay the germ of the Edison quadruplex. It is also noted that "In 1874 Edison invented a method of simultaneous transmission by induced currents, which has given very satisfactory results in experimental trials." Interest in the duplex as a field of invention dwindled, however, as the quadruplex loomed up, for while the one doubled the capacity of a circuit, the latter created three "phantom wires," and thus quadruplexed the working capacity of any line to which it was applied. As will have been gathered from the above, the principle embodied in the quadruplex is that of working over the line with two currents from each end that differ from each other in strength or nature, so that they will affect only instruments adapted to respond to just such currents and no others; and by so arranging the receiving apparatus as not to be affected by the currents transmitted from its own end of the line. Thus by combining instruments that respond only to variation in the strength of current from the distant station, with instruments that respond only to the change in the direction of current from the distant station, and by grouping a pair of these at each end of the line, the quadruplex is the result. Four sending and four receiving operators are kept busy at each end, or eight in all. Aside from other material advantages, it is estimated that at least from $15,000,000 to $20,000,000 has been saved by the Edison quadruplex merely in the cost of line construction in America.
The quadruplex has not as a rule the same working efficiency that four separate wires have. This is due to the fact that when one of the receiving operators is compelled to "break" the sending operator for any reason, the "break" causes the interruption of the work of eight operators, instead of two, as would be the case on a single wire. The working efficiency of the quadruplex, therefore, with the apparatus in good working condition, depends entirely upon the skill of the operators employed to operate it. But this does not reflect upon or diminish the ingenuity required for its invention. Speaking of the problem involved, Edison said some years later to Mr. Upton, his mathematical assistant, that "he always considered he was only working from one room to another.