Of greater scientific interest, perhaps, still, is the "Armor1" wireless controlled torpedo. This is the invention of two gentlemen, Messrs Armstrong and Orling, whose first syllables combine to form the title of the torpedo. Of this, two very interesting features may be mentioned. Firstly, the wireless control. In the chapter on Wireless Telegraphy there is described the coherer, a simple little apparatus which we might describe as a door which is opened by the "waves" which travel through the ether from the sending apparatus. Whenever the key of the sending apparatus is depressed these waves travel forth, and when they fall upon the coherer it "opens." Normally, the coherer is shut, but when acted upon by the incoming waves it opens and lets through current from a battery, which current can be caused to perform any duty which we may wish. Thus, ignoring the intermediate steps, we get this: whenever the sending key is depressed current flows through the coherer and performs whatever duty is set before it. And now picture to yourself a tooth wheel with four teeth. A catch normally holds one of the teeth, but when the catch is lifted for a moment it lets that tooth slip and the next one is caught. At every lifting of the catch the wheel turns a quarter of a turn. Then imagine that that catch is operated by an electro-magnet energised by the current which passes through the coherer. We see, then, that every time the sending key is depressed the wheel turns a quarter turn. Attached to the wheel is a little crank which turns with it, and the pin of this crank fits in a slot in the end of a bar like the tiller of a boat. Suppose that, to commence with, the tiller is straight, so as to steer the boat straight. Depress the key, the wheel turns a quarter turn and the tiller is set so as to steer to one side, say the left. Another pressure upon the key and a second quarter turn brings the tiller straight again. Yet another pressure, another quarter turn, and the tiller is steering to the right. Thus by simply pressing the key the correct number of times the torpedo can be made to travel in any desired direction. The second ingenious feature of this weapon is the means by which it is made visible to the man who is controlling it from the shore or ship. Probably the reason why these torpedoes are not used more is that the man who guides them is of necessity himself visible. He has to be posted somewhere where he can follow its course, or he has no idea how to steer it. Consequently, he would be an object for attack by the enemy. Such a torpedo would be useless in a submarine, for the submarine would need to come to the surface in order that the observer might get a sufficiently good view to be able to steer the torpedo, and we all know that when upon the surface a submarine is a very vulnerable craft.