Before Gerrod could protest they were just skimming the surface of the silver sea. The plane settled gently into the now liquid spot of ocean, and Davis shut off the motors. The occupants of the cabin looked eagerly out of the windows. All about them, in a space perhaps sixty or seventy yards across, the water was yellowed and oily, but was certainly water, and not the horrible, jellylike stuff the world had so much cause to fear. The concussion from the high-explosive bomb had shattered the fragile shells of the silver animalcules, and, with their protection gone, they had relapsed into liquid. At the edge of that space, however, the silver-sea began again, as placid and malignant as before. The plane floated lightly on the surface while the little party congratulated itself. "It works," said Davis proudly. Nita squeezed his hand ecstatically. "I knew he'd think of something," she announced cheerfully. Evelyn and Gerrod were estimating the area of cleared water with gradually lengthening faces. "Let's see how much space a hand grenade clears," suggested Evelyn thoughtfully. Davis opened the case and took out one of the wicked little bombs. He wriggled through a window and out on the massive lower plane of the flying boat. Balancing himself carefully, he flung the grenade some sixty yards into the untouched silver sea. It burst with a cracking detonation and amid a fountain of spume and spray. The four of them eyed the resultant area of clear water. "How wide do you suppose that is?" asked Gerrod rather depressedly. "Ten--no, fifteen yards by fifteen." So excited were they all that they did not notice a phenomenon that began almost instantly. The tiny animalcules that formed the silver sea reproduced rapidly when given merely moisture. Here they had that moisture, and, in addition, the bodies of all their dead comrades to feed upon. The conditions were ideal for nearly instantaneous reproduction. As a result the waves from the high-explosive bombs had hardly subsided when the open space began, almost imperceptibly, to be closed by fresh masses of the Silver Menace. The open space became covered with a thin film which became thicker--thicker---- "And how much explosive was in that grenade?" "Two ounces of TNT." Davis began to catch the drift of the questions, and his happy expression was beginning to fade away. "Two ounces of TNT cleared up roughly a hundred and fifty square yards of silver sea. That's, say, seventy-five square yards to the ounce of high explosive." Evelyn was working rapidly with her pencil. "That works out--five hundred pounds of TNT needed to clear a square mile of the Silver Menace. We have fifteen hundred miles of coast that has been invaded to an average depth of at least five miles." Gerrod took up the calculations with a dismal face. His pencil moved quickly for a moment or so.