"Perhaps," said the old reservist, "but you have forgotten about the howitzers." "Why, yes, so I had," the doctor answered, more gravely; "you were going to tell me about them." "The difference in principle between a gun and a howitzer or a mortar," explained the master, "is that a gun depends for its destructiveness on its striking velocity, while a howitzer depends on the power of the exploding charge of its shell. An armor-piercing shell, fired from a 15-inch naval gun, will go through the heaviest and hardest steel known, because of the terrific speed at which it travels, with a muzzle velocity of three thousand feet a second or thirty-four miles a minute. In order not to lose speed, therefore, it must travel in as straight a line as possible. In other words, a missile from a gun must have a long low curve or trajectory." "Yes," said the doctor, "I can see that." "A howitzer, on the other hand," the master explained, "does not require any more velocity than just to carry the high-explosive shell to the point designed. Moreover, in order that their terrible effects may be the more destructive, mortars and howitzers drop their shells from overhead upon the object of fire by lobbing them up in the air with a very high trajectory. A howitzer generally looks as though it were shooting at the moon. It can be placed in a valley and fire over the hill. But, as you can see, its range is restricted. A naval gun throwing an 8-inch shell may have a range of sixteen miles, while the 8-inch howitzer operates best from three or four miles away. "You see, Doctor," he continued, "if our defenses have been constructed upon the basis of attack from heavy field-guns and light howitzers--which is the system of most European armies--if our energy has been spent on disappearing cupolas and sunken masonry works which will resist gun-fire, is there not a terrible danger if we are attacked by heavy howitzers, dropping high explosive shells from overhead? To such shells it will make no difference whether the cupolas be raised or lowered. "If it be true," the old reservist added, his voice rising with a note of presage, "if it be true what is whispered about these new German siege howitzers, then destruction will rain upon the forts of Liége as though the skies were a mouth of flame. "Perhaps never before, in the history of the world, has so much hung upon the range and power of a modern weapon. We await the eruption of a man-forged volcano which may engulf us all in its fiery lava." The doctor passed his hand over his face and looked up unconsciously, half in fear as though the doom was on them. "You make it very ugly," he said. The master paced on through the late dusk, a glow from the distant gunfire mingling with the faint starlight on his face. "It matters very little if the End be ugly," he replied, "so long as the road be that of heroism."