Owing to the difficulty of constructing in France enough telegraph and telephone lines to meet the constantly increasing requirements of the American Expeditionary Forces, as well as to relieve the great congestion which prevailed on all of the existing lines, the scientists of the Signal Corps turned their attention early in the war to the possibility of sending several messages simultaneously over a single wire. Without entering into the details of the long series of experiments which were conducted by the Signal Corps, in conjunction with the American Telephone and Telegraph Company at Camp Alfred Vail, New Jersey, or attempting to describe in terms which would be intelligible to the non-technical reader the device which was finally perfected, it may be said that the result is accomplished through the application of radio, the wire serving as a guide for the radio currents and conducting them with a minimum of power and with a minimum of interference with other radio communications. This device has now been brought to such a state of perfection that eight telegraph messages and eleven telephone messages can be carried over a single wire at the same time, the Morse messages being transmitted by means of the multiplex telegraph apparatus—a system which was discovered as early as 1910 and is now in general use by the large telegraph companies—while the telephone conversations are guided by wireless waves, which serve as carriers for the voice currents. By placing on ordinary telegraph-wires wireless waves of very short length or of very great frequency, officers of the Signal Corps have successfully conversed over a line from Washington to Baltimore which was being used at the same time for the transmission of duplex telegraph messages. Perhaps the most remarkable feature of the performance was its extreme simplicity, the feat being accomplished merely by placing on the line, through proper connecting condensers, a pair of radiotelephone sets such as are used for communicating between ground-stations and airplanes. Whereas it was believed, until very recently, that it was impracticable to hold more than four wired-wireless conversations over one wire or one pair of wires, in addition to whatever ordinary telephone or telegraph conversation might be on that wire, the Signal Corps has now demonstrated that it is not only possible but entirely practicable to hold ten or more extra telephone conversations without their interfering with each other. Had this system been perfected while the war was in progress it would have meant that ten telephone and two or more telegraph conversations could have been carried on simultaneously with a point served only by a single wire. In other words, by the application of this system one wire will take the place of ten.