For the longer lines away back from the fighting the methods employed are just the same as those of peace. "Sounder" instruments are used, Wheatstone automatic machines, duplex and quadruplex systems, whereby two and four messages are sent simultaneously over the same wire, indeed all the contrivances and refinements of the home telegraph office are to be found in the field telegraph offices. But it would hardly be fitting to describe them here. Some information on the subject will be found in "The Romance of Submarine Engineering," where their application to cable telegraphy is dealt with. A genuine speciality of warfare, however, is the methods by which makeshift arrangements can be set up, such as sending telegraph messages over a telephone wire without interfering with the latter. Imagine that A and B are the two wires of a telephone circuit running (for the sake of simplicity) from north to south. At the south end I connect a telegraph set to both wires while you, we will imagine, do the same at the north end. You and I can then signal to each other without the telephone man hearing us at all. To him the two wires are flow and return, to us they are both "flow," the earth being our return. Thus our signals never reach his instruments at all. But when we each connect to both his wires, do we not "short-circuit" or connect them to each other, thereby destroying his circuit? No, we are too cunning for that. We first connect the two wires A and B together with a coil of closely wound wire, having, in scientific language, much "inductance," and telephone currents shun a coil of that sort. Then we make our connection to the centre of that coil so that our currents go to A through half the coil and to B through the other half. This enables us to use the apparatus without interfering with the other fellow at all. For this, by the way, we must use ordinary telegraph instruments. We cannot employ a buzzer, for these coils which we use to obstruct the passage of the other man's telephone currents would also obstruct the changing currents from a buzzer. The slow, steady currents of the ordinary telegraph pass quite easily, however. Again, suppose you and I want to communicate by buzzer and there is already a wire laid passing both of us but in use already for ordinary telegraphy. We only need to add a "condenser" to our apparatus and we can manage all right. As a matter of fact, the service instruments generally have condensers partly for this very purpose. Each of us then connects his instrument to the wire and to earth, after which we can signal to each other while the telegraphist is unaware of the fact. The reason that is possible is the reverse of what we saw just now. There we had a coil which obstructed buzzer or telephone currents but passed ordinary telegraph currents. Here we use condensers which will pass our buzzer currents but not the ordinary telegraph currents.