In meeting the attack of any enemy at night, search-light shell are sometimes used. On exploding they discharge a number of "candles," each provided with a tiny parachute that lets the candle drop slowly to the ground. Their brilliant light lasts fifteen or twenty minutes. Obviously, ordinary search-lights could not be used on the battle-field, because the lamp would at once be a target for enemy batteries, but with search-light shell the gun that fires them can remain hidden and one's own lines be shrouded in darkness while the enemy lines are brilliantly illuminated. CHAPTER V THE BATTLE OF THE CHEMISTS Some years ago the nations of the world gathered at the city of The Hague, in Holland, to see what could be done to put an end to war. They did not accomplish much in that direction, but they did draw up certain rules of warfare which they agreed to abide by. There were some practices which were considered too horrible for any civilized nation to indulge in. Among these was the use of poisonous gases, and Germany was one of the nations that took a solemn pledge not to use gas in war. [Illustration: (C) Kadel & Herbert Even the Horses had to be Masked] [Illustration: Photograph by Kadel & Herbert Portable Flame-throwing Apparatus] Eighteen years later the German Army had dug itself into a line of trenches reaching from the English Channel to Switzerland, and facing them in another line of trenches were the armies of France and England, determined to hold back the invaders. Neither side could make an advance without frightful loss of life. But a German scientist came forth with a scheme for breaking the dead-lock. This was Professor Nernst, the inventor of a well-known electric lamp and a man who had always violently hated the British. His plan was to drown out the British with a flood of poisonous gas. To be sure, there was the pledge taken at The Hague Conference, but why should that stand in Germany's way? What cared the Germans for promises now? Already they had broken a pledge in their violation of Belgium. Already they had rained explosives from the sky on unfortified British cities (thus violating another pledge of The Hague Conference); already they had determined to war on defenseless merchantmen. To them promises meant nothing, if such promises interfered with the success of German arms. They led the world in the field of chemistry; why, they reasoned, shouldn't they make use of this advantage? POURING GAS LIKE WATER