A TANK _Frontispiece_ PAGE MACHINE-GUN VERSUS RIFLE 32 AN ITALIAN MINE-LAYER 64 AN INCIDENT AT LOOS 80 AN 18-POUNDER IN ACTION 96 A GERMAN AUTOMATIC PISTOL 112 BOMB THROWING 136 BOMB-THROWERS AT WORK 160 THE TRIPOD MAST 208 LISTENING FOR THE ENEMY 248 DIAGRAM SHOWING THE PRINCIPLE BY WHICH THE AERIALS ARE CONNECTED TO THE APPARATUS 251 THE PARENT OF THE TANK 280 THE "GUARDIAN ANGEL" PARACHUTE 304 THE ROMANCE OF WAR INVENTIONS CHAPTER I HOW PEACEFUL ARTS HELP IN WAR In the olden times warfare was supported by a single trade, that of the armourer. Nowadays the whole resources of the greatest manufacturing nations scarcely suffice to supply the needs of their armies. So much is this the case that no nation can possibly hope to become powerful in a military or naval sense unless they are either a great manufacturing community or can rely upon the support of some great manufacturing ally or neutral. It is most astonishing to find how closely some of the most innocent and harmless of the commodities of peace are related to the death-dealing devices of war. Of these no two examples could be more striking than the common salt with which we season our food and the soap with which we wash. Yet the manufacture of soap furnishes the material for the most furious of explosives and the chief agent in its manufacture is the common salt of the table. Common salt is a combination of the metal sodium and the gas chlorine. There are many places, of which Cheshire is a notable example, where vast quantities of this salt lie buried in the earth. Fortunately it is very easily dissolved in water so that if wells be sunk in a salt district the water pumped from them will have much salt in solution in it. This is how the underground deposits are tapped. It is not necessary for men to go down as they do after coal, for the water excavates the salt and brings it to the surface. To obtain the solid salt from the salt water, or brine as it is called, it is only necessary to heat the liquid, when the water passes away as steam leaving the salt behind. Important though this salt is in connection with our food, it is perhaps still more important as the source from which is derived chlorine and caustic soda. How this is done can best be explained by means of a simple experiment which my readers can try in imagination with me or, better still, perform for themselves.