Although the printing and automatic systems of telegraphing are used in America to some extent, the larger part is done by the Morse system of sound-reading and copying from it, either by pen or the typewriter. In the early days only one message could be sent over one wire at the same time, but now from four to six or even more messages may be sent over the same wire simultaneously without one message interfering with the other. Like most other inventions, many inventors have contributed to the development of multiple transmission, till finally some one did the last thing needed to make it a success. The first attempts were in the line of double transmission, and many inventors abroad have worked on this problem. Moses G. Farmer of Salem, Mass., proposed it as early as 1852, and patented it in 1858. Gintl, Preece, Siemens and Halske and others abroad had from time to time proposed different methods of double transmission, but no one of them was a perfect success. When the line was very long there was a difficulty that seemed insurmountable. In the common parlance of telegraphy, there was a "kick" in the instrument that came in and mutilated the signals. About 1872 Joseph B. Stearns of Boston made a certain application of what is called a "condenser" to duplex telegraphy that cured the "kick," and from that time to this it has been a success. Farther along I will tell you what occasioned this "kick" and how it was cured. If this or some other method could be applied as successfully to cure the many chronic "kickers" in the world it would be a great blessing to mankind. It has always been a mystery to the uninitiated how two messages could go in opposite directions and not run into one another and get wrecked by the way. If you will follow me closely for a few minutes I will try to tell you. We have already stated that an electromagnet is made by winding an insulated wire around a soft iron core. If we pass a current of electricity through this wire the core becomes magnetic, and remains so as long as the current passes around it. In duplex telegraphy we use what is called a differential magnet. A differential electromagnet is wound with two insulated wires and so connected to the battery that the current divides and passes around the iron core in opposite directions. Now if an equal current is simultaneously passed through each of the wires of the coil in opposite directions the effect on the iron will be nothing, because one current is trying to develop a certain kind of polarity at each pole of the magnet, while the current in the other wire is trying to develop an opposite kind in each pole. There is an equal struggle between the two opposing forces, and the result is no magnetism. This assumes that the two currents are exactly the same strength.