Many young readers, scouts, members of cadet corps and the like, will find great pleasure and interest in constructing and working this apparatus, besides which it shows precisely what the official "buzzer" is like. Although beautifully made, of course, the army instrument is essentially just that and little more. It has an additional feature, however, namely, a microphone, so that when desired it can be used as a speaking telephone for transmitting verbal messages. It also has the bottom of the case made of a brass plate so that earth pins are often unnecessary, the case dumped down upon the ground being a good enough "earth." Buzzers are not used for very long lines: forty miles is about the limit, and usually the distances are very much less. That is because long lines rather object to rapidly changing currents flowing through them. Why, you say, what currents could change more rapidly than telephone currents carrying speech, yet they go for hundreds of miles? True, but in that case there are two wires, flow and return, twisted together all the way, under which conditions they interact upon each other in such a manner as to abolish the difficulty to which I am referring. Buzzers and indeed all the telegraph circuits consist of one wire and the earth, which is quite different. Another objection to the buzzer is that it is apt to interfere with others. For instance, if two buzzer sets are at work anywhere near each other and the wires run parallel for a distance they will be able to hear each other's signals as well as their own. If two such sets are earthed near together the same thing happens, the signals of one are picked up by the other, a very annoying state of affairs for the operators. Right at the front, however, amid the rough and tumble of the actual fighting, the buzzer is supreme. The wire used is sometimes plain copper enamelled: more often, however, it is a mixture of steel and copper strands twisted together and covered with a strong insulating covering. This is carried on reels in properly fitted carts which can advance at a gallop, paying out the wire as they go. The inner end of the wire is connected to the axle of the reel in such a way that a telegraphist in the cart is in communication all the time with the starting-point, the wheels of the cart providing him with an earth connection. When laying these wires another interesting little device is often used--an earth plate on the operator's heel. Thus, while carrying the wire along, laying it as he goes, he can still be in communication with the starting-point every time he puts his heel to the ground.