Teddy Gerrod straightened up and beat his hands together.

"Forty-seven below," he said to the soldier behind him. "Put a marker here."

He moved off to the right. Already a dozen little flags showed where the temperature reached that degree. Teddy was drawing what he would have termed an isothermal line—a line where the temperature was the same. He was making a circle about a large part of the open clearing on the ice floe. Other flags led back into the mist, marking a path, and from time to time a party of four or five fur-clad soldiers arrived from the fort, dragging a loaded sledge behind them. They emptied the load from the sled, turned, and vanished into the mist again. A small pile of drills, explosives, and two of the squat trench mortars had already been made.

When the circle of little red flags had been completed, two signal-corps men set up their instruments and accurately located the center. Directly under that spot, if Teddy's reasoning was correct, the new cold bomb was resting. The sledge from the fort arrived again, bearing a curious trench catapult for flinging bombs. Four long strips of black cloth were unrolled, under direction of the signal-corps men, pointing accurately to the center of the circle. No one had been able to approach nearer, thus far, than thirty yards from the center. At that distance Teddy's thermocouple indicated a temperature of more than seventy-two degrees below zero, and flesh exposed to the air was frostbitten on the instant. What the temperature of the air might be directly above the cold bomb could only be conjectured.

One of the infantry men from the fort, the best grenade man in the garrison, now picked up a Mills grenade, and after carefully picking out the target with his eye, aided by the strips of black cloth, flung the small missile. A hole perhaps four feet deep and twice as much across was blasted in the brittle ice. A second, third, and fourth grenade followed. At the end of that time the size and depth of the hole had been doubled.

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.

"We must be pretty nearly at the cold bomb now," said Teddy thoughtfully. "There's a mass of liquid air at the bottom of our crater, and something tells me there's solidified air at the bottom of that puddle. That means seven hundred-odd degrees below zero."

He was clad in the warmest garments that could be found, and every one of the others working in the clearing was quite as warmly clothed, but the cold was intense. One of the soldiers by the small pile of explosives was chewing a cud of tobacco. He spat. The brownish liquid froze in mid-air and bounced merrily away across the ice. The soldier looked at it with his mouth open, then shut it quickly. A thin film of ice had formed from the moisture on his teeth. The breast of every member of the party was covered with sparkling snow crystals from the congealed moisture of their breath.

"I begin to doubt if we can keep our stuff from freezing much deeper," Teddy commented. "We want to go down as deep as we can before we use our Dewey bulbs, though. I've only two of them."

The young lieutenant bustled away, and presently returned.

"The men say that the last bomb won't go off," he said aggrievedly. "Your heating plan doesn't work."

"I didn't expect it to work indefinitely," said Teddy mildly. "We want to clear out that liquid air and shoot our two Dewey globes before it's had time to reform. Will you please have a charge made ready to be fired just above the surface of that puddle? That should clear it away. Immediately after that charge has gone off we'll drop our two T. N. T. charges in the Dewey bulbs. They ought to show us the cold bomb."

The dynamite charge was suspended about a foot above the surface of the watery, bubbling pool. Air was in that pool, air turned to transparent liquid by the intense cold. At -325° Fahrenheit air becomes a liquid. Here, exposed to the sunlight and the blue sky, a pool of liquified gas had collected from the incredible cold of the cold bomb below. The charge of explosive burst with a shattering roar. The echoes of the explosion had not died away when the two Dewey bulbs filled with T. N. T. fell into the bared ice cavity. A Dewey bulb is a combination of six vacuum bottles placed one outside the other. They are used for the keeping of liquid gases at a low temperature, but are obviously just as effective in protecting their contents from exterior cold. They fell some five yards apart and rolled, then were still. Their fuses sputtered. They went off together. A huge mass of shattered ice was thrown aside, and a dark, globular mass was exposed to view. Almost as soon as it was exposed to the air a crust of frozen air coated it, and liquified air began to trickle down its misshapen sides. There could be no doubt but that it was the cold bomb, invented by an insane genius to make him master of the world.

Those about the rim of the crater looked at it and turned away. Just as the intense heat of a blast furnace sears unprotected flesh even yards from its flame, so the incredible cold of the dark object pinched and wrung with its freezing rays. Not one man who looked upon the cold bomb but suffered from a deep frostbite.

"We can't approach that thing," said Teddy, with his hand over his eyes. "I'd just as soon, or sooner, try to tinker with burning thermite. We'll have to shoot armor-piercing shells at it. They'll freeze when they get near it, but the impact ought to crack the thing."

He motioned to the fur-clad soldiers to move back from the crater, and after a hasty consultation with the lieutenant went off toward the fort to ask for a small-caliber field gun.

The lieutenant paced back and forth restlessly. He was an ambitious young man. He did not relish taking orders from a civilian like Teddy. His eye fell on the heap of equipment that had been brought out from the fort. Two trench mortars, a trench catapult, a liquid-flame apparatus—one of the American inventions that had far outdone the original German flamenwerfers! There had been some thought of trying to reach a point just above the cold bomb and melting the ice down to it with liquid flame. That had been quickly proven impracticable, but the liquid-fire apparatus had not been sent back. The young lieutenant was not stupid. On the contrary, he was a singularly intelligent man. In a flash he saw how the liquid flame could have been used much more efficiently than Teddy's resistance coils about his explosive charges. The idea simply had not occurred to Teddy, or the young lieutenant, either. Now, however, he became all eagerness. If he succeeded in breaking up the cold bomb during Teddy's absence it would be a feather in his cap. If, in addition, he pointed out a method of dealing with the cold bombs superior to Teddy's plodding system, it would certainly mean his promotion and a very desirable reputation for himself in his profession.

He gave his orders briskly. The liquid-flame tank was set up, and began to spray out its stream of fire. The young lieutenant had it trained so that it passed just above the top of the ungainly cold bomb and grazed the upper edge. Then the two trench mortars were made ready for firing. The young lieutenant set them at their proper elevation himself. He was tremendously excited. He pointed the two mortars with the most meticulous precision. To aim them properly he had to expose his face again and again to the direct rays from the cold bomb, but he paid no attention to the searing, freezing rays.

The stream of liquid fire shot upward in a perfect parabola, and fell evenly, exactly, where it was aimed. The young lieutenant knew that a mortar bomb would be frozen by the intense cold if it were fired at the cold bomb direct, but his plan got around that difficulty. With the liquid fire playing just above and grazing the cold bomb, when the shell from the mortar struck the incredibly cold surface, both the shell and the cold bomb would be bathed in flame.

All was ready. The lieutenant fixed his eyes on the cold bomb and gave the signal. The two small trench mortars spouted flame. Two ungainly bombs rose high in the air and fell hurtling down toward the strange, frosted object at the bottom of the crater. One of the bombs would fall a little to the left. The other—squarely on top!

The cracking explosion of the bomb from the trench mortar was lost in the greater roar that followed it. Before the young lieutenant or any of his men could lift a finger they were enveloped by a colossal sheet of vaporized metal that seemed to fill the earth, the air, and all the sky. Of a weird and unearthly tint, the white-hot flame leaped into the air. It sprang up three thousand feet in hardly more than two seconds. The blast had the velocity of many rifle balls, and the withering heat of molten metal. The young lieutenant and his men were swept into nothingness in the fraction of a second. The crater they had worked for hours to blast out was as a puny ant hole beside the vast chasm that opened in the ice down to the red clay far beneath the bed of the Narrows. And New York shook and trembled from the shock of the terrific explosion.