The trench catapult was set up. Half a dozen grenades were bundled together and flung into the now much enlarged opening in the surface of the ice. There was no explosion. One automatically braced oneself for the report, and the utter silence that succeeded the disappearance of the grenades came as a peculiar shock. "Too cold," remarked Teddy to the young lieutenant in charge. The lieutenant nodded stiffly. "We'll try again." A second batch of grenades was flung into the hole, and the same quiet resulted. "I would suggest----" Teddy begin. "We'll fire a trench-mortar bomb," said the young lieutenant. The heavy winged projectile flew up into the air, and then descended squarely into the opening in the ice. Those standing fifty yards away could hear the crash as it struck, and then a sound as of musical splintering. The young lieutenant swore. "The fuses are no good. Try once more." "You can shoot all day and they won't go off," said Teddy mildly. "It's too cold down there." The officer said nothing, but supervised the firing of a second mortar bomb with precisely the same result. He swore again. "It's probably quite as cold as liquid air down there," said Teddy. "In fact, there's quite possibly a pool of liquified air at the bottom of the hole. Your bombs fall into that air and are frozen so solidly before they strike that the metal gets brittle and simply falls to powder from the shock. You can't do anything going on this way." The young lieutenant hesitated, then turned to Teddy somewhat sulkily. "What do you suggest, then?" "We'd better enlarge the hole first. Blast down the walls of the present cavity, then use wrapped dynamite until we have a shallow crater. Then we'll place our explosives by long poles, keeping them warm by running resistance wires around them and heating them electrically." The young lieutenant considered and agreed. Teddy went back to the fort to arrange for the heated bombs and the long poles. When he returned there was only a saucerlike depression in the ice clearing. It was quite fifty yards across, but no more than twenty deep. Standing near the edge, one could see the ice near the bottom glistening liquidly. Air, liquified by the intense cold at the bottom of the crater, wet the surface of the ice there. "And that means the temperature down there is three hundred and twenty-five degrees or more below zero Fahrenheit," explained Teddy casually. "Here's where we use our heated explosives." For an hour the party worked busily. Storage batteries brought out on sledges furnished the current that kept the explosives from becoming inert through cold. Charge after charge was fired, and the bottom of the crater grew steadily deeper. At the lowest point a little puddle of liquified air collected.