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.
"We'd need over eighteen hundred tons of TNT to clear our coasts," he said dolefully. "That wouldn't touch the silver sea itself or keep it from growing again. It grew inland those five miles in two weeks at most. That's nine hundred tons a week needed to hold our own without attacking the silver sea at all. We'd have to have forty-six thousand tons a year to hold it, let alone go after the beasts out here, and in the meantime we'll have no rain, consequently no crops. It's a cheerful outlook."
They had been oblivious of what was happening immediately about the seaplane.
Nita first saw the danger.
"Look!" she gasped.
They had been too much absorbed in gloomy thoughts to notice their predicament. The open space in which they had landed was now a shining, glittering mass of the Silver Menace. But what Nita pointed to was of more imminent danger. The sticky, horrible mass was creeping up the float on which the seaplane rode and up the smaller floats at the ends of the wings. Tons of the silver horror had already accumulated upon the under surface of the great planes and weighted down the aëroplane until it was impossible for it to rise in the air. And it continued to creep up and over the body. In a little while the seaplane would be overwhelmed by the viscid, evil-smelling, deadly little animalcules.