The major was marking the position of the last man, completing his circle under which the cold bomb must lie, when a peculiar tremor was felt by every man there. It was not like the shiver of an earthquake or the reverberation of an explosion. It was an infinitely shrill vibration that a moment later was followed by a creaking sound that seemed to come from the center of the ice cake. The men on the ice stopped their stamping and swinging of arms to listen in instinctive apprehension.
The center of the circle around which they stood seemed to rise in the air. The ice on which they stood was shivered into tiny fragments. A colossal and implacable roar filled the air, and a great sheet of flame of the unearthly tint of a vaporized metal rose to the heavens. The swathed and bundled soldiers were annihilated by the blast. A great hole five hundred feet across gaped in the center of the ice cake. Jacksonville shook from the concussion, and the plate-glass windows of its stores and office buildings splintered into a myriad tiny bits that sprinkled all its streets with sharp-edged, jagged pieces.
Teddy Gerrod, all unconscious of the fate of those who had attempted to meddle with the Jacksonville ice cake, went on out to bare and blast open the cold bomb that blocked New York harbor.
CHAPTER VI.
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."