For several minutes Carnes swung the telescope around. Twice Dr. Bird stopped him and decreased the sensitiveness of his instrument by introducing more resistance in the lines in order to keep the magnet from twisting clear around, due to the fluctuations in the heats received on account of the varying conditions of reflection. As Carnes swung the telescope again the magnet swung around sharply, nearly to a right angle to its former position.
"Stop!" cried the doctor. "Read your azimuth."
Carnes read the compass bearing on the protractor attached to the frame which supported the telescope. Dr. Bird took a pair of binoculars and looked long and earnestly in the indicated direction. With a sigh he laid down the glasses.
"I can't see a thing, Carnesy," he said. "We'll have to move over to the next crest and make a new set-up. Plant a rod on the hill so that we can get an azimuth bearing and get the airline distance with a range finder."
On the hilltop which Dr. Bird had pointed out the apparatus was again set up. For several minutes Carnes swept the hills before an exclamation from the doctor told him to pause. He read the new azimuth, and the doctor laid off the two readings on a sheet of paper with a protractor and made a few calculations.
"I don't know," he said reflectively when he had finished his computations. "This darned instrument is still so sensitive that you may have merely focused on a deep shadow or a cold spring or something of that sort, but the magnet kicked clear around and it may mean that we have located what we are looking for. It should be about two miles away and almost due west of here."
"There is no spring that I know of, Doc, and I think I know of every water hole in this country," remarked Bill.
"There could hardly be a spring at this elevation, anyway," replied the doctor. "Maybe it is what we are seeking. We'll start out in that direction, anyway. Bill, you had better take the lead, for you know the country. Spread out a little so that we won't be too bunched if anything happens."
For three-quarters of an hour the little group of men made their way through the wilderness in the direction indicated by the doctor. Presently Bill, who was in the lead, held up his hand with a warning gesture. The other three closed up as rapidly as cautious progress would allow.
"What is it, Bill?" asked the doctor in an undertone.
"Slip up ahead and look over that crest."
The doctor obeyed instructions. As he glanced over he gave vent to a low whistle of surprise and motioned for Carnes to join him. The operative crawled up and glanced over the crest. In a hollow before them was a crude one-storied house, and erected on an open space before it was a massive piece of apparatus. It consisted of a number of huge metallic cylinders, from which lines ran to a silvery concave mirror mounted on an elaborate frame which would allow it to be rotated so as to point in any direction.
"What is it?" whispered Carnes.
"Some kind of a projector," muttered the doctor. "I never saw one quite like it, but it is meant to project something. I can't make out the curve of that mirror. It isn't a parabola and it isn't an ellipse. It must be a high degree subcatenary or else built on a transcendental function."
He raised himself to get a clearer view, and as he did so a puff of smoke came from the house, to be followed in a moment by a sharp crack as a bullet flattened itself a few inches from his head. The doctor tumbled back over the crest out of sight of the house. Bill and Walter hurried forward, their rifles held ready for action.
"Get out on the flanks, men," directed the doctor. "The man we want is in a house in that hollow. He's armed, and he means business."
Bill and Walter crawled under the shelter of the rocks to a short distance away and then, rifles ready, advanced to the attack. A report came from the hollow and a bullet whined over Bill's head. Almost instantly a crack came from Walter's rifle and splinters flew from the building in the hollow a few inches from a loophole, through which projected the barrel of a rifle.
The rifle barrel swung rapidly in a circle and barked in Walter's direction; but as it did so, Bill's gun spoke and again splinters flew from the building.
"Good work!" ejaculated Dr. Bird as he watched the slow advance of the two guides. "If we just had rifles we could join in the party, but it's a little far for effective pistol work. Let's go ahead, and we may get close enough to do a little shooting."
Pistols in hand, Carnes and the doctor crawled over the crest and joined the advance. Again and again the rifle spoke from the hollow and was answered by the vicious barks of the rifles in the hands of the guides, Carnes and the doctor resting their pistols on rocks and sending an occasional bullet toward the loophole. The conditions of light and the moving target were not conducive to good marksmanship on the part of the besieged man, and none of the attackers were hit. Presently Walter succeeded in sending a bullet through the loophole. The rifle barrel suddenly disappeared. With a shout the four men rose from their cover and advanced toward the building at a run.
As they did so an ominous whirring sound came from the apparatus in front of the house and a sudden chill filled the air.
"Back!" shouted Dr. Bird. "Back below the hill if you value your lives!"
He turned and raced at full speed toward the sheltering crest of the hill, the others following him closely. The whirring sound continued, and the concave reflector turned with a grating sound on its gears. As the path of its rays struck the ground the rocks became white with frost and one rock split with a sharp report, one fragment rolling down the slope, carrying others in its trail.
With panic-stricken faces the four men raced toward the sheltering crest, but remorselessly the reflector swung around in their direction. The intense cold numbed the racing men, cutting off their breath and impeding their efforts for speed.
"Stop!" cried the doctor suddenly. "Fire at that reflector! It's our only chance!"
He set the example by turning and emptying his pistol futilely at the turning mirror. Bill, Walter and Carnes followed his example. Nearer and nearer to them came the deadly ray. Bill was the nearest to its path, and he suddenly stiffened and fell forward, his useless gun still grasped in his hands. As his body struck the ground it rolled down hill for a few feet, the deadly ray following it. His head struck a rock, and Carnes gave a cry of horror as it broke into fragments.
Walter threw his rifle to his shoulder and fired again and again at the rotating disc. The cold had became intense and he could not control the actions of his muscles and his rifle wavered about. He threw himself flat on the ground, and, with an almost superhuman effort, steadied himself for a moment and fired. His aim was true, and with a terrific crash the reflector split into a thousand fragments. Dr. Bird staggered to his feet.
"It's out of order for a moment!" he cried. "To the house while we can!"
As swiftly as his numbed feet would allow him, he stumbled toward the house. The muzzle of the rifle again projected from the loophole and with its crack the doctor staggered for a moment and then fell. Walter's rifle spoke again and the rifle disappeared through the loophole with a spasmodic jerk. Carnes stumbled over the doctor.
"Are you hit badly?" he gasped through chattering teeth.
"I'm not hit at all," muttered the doctor. "I stumbled and fell just as he fired. Look out! He's going to shoot again!"
The rifle barrel came slowly into view through the loophole. Walter fired, but his bullet went wild. Carnes threw himself behind a rock for protection.
The rifle swung in Walter's direction and paused. As it did so, from the house came a strangled cry and a sound as of a blow. The rifle barrel disappeared, and the sounds of a struggle came from the building.
"Come on!" cried Carnes as he rose to his feet, and made his stumbling way forward, the others following at the best speed which their numbed limbs would allow.
As they reached the door they were aware of a struggle which was going on inside. With an oath the doctor threw his massive frame against the door. It creaked, but the solid oak of which it was composed was proof against the attack, and he drew back for another onslaught. From the house came a pistol shot, followed by a despairing cry and a guttural shout. Reinforced by Carnes, the doctor threw his weight against the door again. With a rending crash it gave, and they fell sprawling into the cabin. The doctor was the first one on his feet.
"Who are you?" asked a voice from one corner. The doctor whirled like a flash and covered the speaker with his pistol.
"Put them up!" he said tersely.
"I am unarmed," the voice replied. "Who are you?"
"We're from the United States Secret Service," replied Carnes who had gained his feet. "The game is up for you, and you'd better realize it."
"Secret Service! Thank God!" cried the voice. "Get Koskoff--he has the plans. He has gone out through the tunnel!"
"Where is it?" demanded Carnes.
"The entrance is that iron plate on the floor."
Carnes and the doctor jumped at the plate and tried to lift it, without result. There was no handle or projection on which they could take hold.
"Not that way," cried the voice. "That cover is fastened on the inside. Go outside the building; he'll come out about two hundred yards north. Shoot him as he appears or he'll get away."
The three men nearly tumbled over each other to get through the doorway into the bitter cold outside. As they emerged from the cabin the gaze of the guide swept the surrounding hills.
"There he goes!" he cried.
"Get him!" said Carnes sharply.
Walter ran forward a few feet and dropped prone on the ground, cuddling the stock of his rifle to his cheek. Two hundred yards ahead a figure was scurrying over the rocks away from the cabin. Walter drew in his breath and his hand suddenly grew steady as his keen gray eyes peered through the sights. Carnes and the doctor held their breath in sympathy.
Suddenly the rifle spoke, and the fleeing man threw up his arms and fell forward on his face.
"Got him," said Walter laconically.
"Go bring the body in, Carnes," exclaimed the doctor. "I'll take care of the chap inside."
"Did you get him?" asked the voice eagerly, as the doctor stepped inside.
"He's dead all right," replied the doctor grimly. "Who the devil are you, and what are you doing here?"
"There is a light switch on the left of the door as you come in," was the reply.
Dr. Bird found the switch and snapped on a light. He turned toward the corner from whence the voice had come and recoiled in horror. Propped in the corner was the body of a middle-aged man, daubed and splashed with blood which ran from a wound in the side of his head.
"Good Lord!" he ejaculated. "Let me help you."
"There's not much use," replied the man rather faintly. "I am about done in. This face wound doesn't amount to much, but I am shot through the body and am bleeding internally. If you try to move me, it may easily kill me. Leave me alone until your partners come."
The doctor drew a flask of brandy from his pocket and advanced toward the corner.
"Take a few drops of this," he advised.
With an effort the man lifted the flask to his lips and gulped down a little of the fiery spirit. A sound of tramping feet came from the outside and then a thud as though a body had been dropped. Carnes and Walter entered the cabin.
"He's dead as a mackerel," said Carnes in answer to the doctor's look. "Walter got him through the neck and broke his spinal cord. He never knew what hit him."
"The plans?" came in a gasping voice from the man in the corner.
"We got them, too," replied Carnes. "He had both packets inside his coat. They have been opened, but I guess they are all here. Who the devil are you?"
"Since Koskoff is dead, and I am dying, there is no reason why I shouldn't tell you," was the answer. "Leave that brandy handy to keep up my strength. I have only a short time and I can't repeat.
"As to who I am or what I was, it doesn't really matter. Koskoff knew me as John Smith, and it will pass as well as any other name. Let my past stay buried. I am, or was, a scientist of some ability; but fortune frowned on me, and I was driven out of the world. Money would rehabilitate me--money will do anything nowadays--so I set out to get it. In the course of my experimental work, I had discovered that cold was negative heat and reacted to the laws which governed heat."
"I knew that," cried Dr. Bird; "but I never could prove it."
"Who are you?" demanded John Smith.
"Dr. Bird, of the Bureau of Standards."
"Oh, Bird. I've heard of you. You can understand me when I say that as heat, positive heat is a concomitant of ordinary light. I have found that cold, negative heat, is a concomitant of cold light. Is my apparatus in good shape outside?"
"The reflector is smashed."
"I'm sorry. You would have enjoyed studying it. I presume that you saw that it was a catenary curve?"
"I rather thought so."
"It was, and it was also adjustable. I could vary the focal point from a few feet to several miles. With that apparatus I could throw a beam of negative heat with a focal point which I could adjust at will. Close to the apparatus, I could obtain a temperature almost down to absolute zero, but at the longer ranges it wasn't so cold, due to leakage into the atmosphere. Even at two miles I could produce a local temperature of three hundred degrees below zero."
"What was the source of your cold?"
"Liquid helium. Those cylinders contain, or rather did contain, for I expect that Koskoff has emptied them, helium in a liquid state."
"Where is your compressor?"
"I didn't have to use one. I developed a cold light under whose rays helium would liquefy and remain in a state of equilibrium until exposed to light rays. Those cylinders had merely enough pressure to force the liquid out to where the sun could hit it, and then it turned to a gas, dropping the temperature at the first focal point of the reflector to absolute zero. When I had this much done, Koskoff and I packed the whole apparatus here and were ready for work.
"We were on the path of the transcontinental air mail, and I bided my time until an especially valuable shipment was to be made. My plans, which worked perfectly, were to freeze the plane in midair and then rob the wreck. I heard of the jewel shipment the T. A. C. was to carry and I planned to get it. When the plane came over, Koskoff and I brought it down. The unsuspected presence of another plane upset us a little, and I started to bring it down. But we had been all over this country and knew there was no place that a plane could land. I let it go on in safety."
"Thank you," replied Carnes with a grimace.
"We robbed the wreck and we found two packets, one the jewels I was after, and the other a sealed packet, which proved to contain certain War Department plans. That was when I learned who Koskoff was. I had hired him in San Francisco as a good mechanic who had no principles. He was to get one-fourth of the loot. When we found these plans, he told me who he was. He was really a Russian secret agent and he wanted to deliver the plans to Russia. I may be a thief and a murderer, but I am not yet ready to betray my country, and I told him so. He offered me almost any price for the plans; but I wouldn't listen. We had a serious quarrel, and he overpowered me and bound me.
"We had a radio set here and he called San Francisco and sent some code message. I think he was waiting here for someone to come. Had we followed our original plans, we would have been miles from here before you arrived.
"He had me bound and helpless, as he thought, but I worked my bonds a little loose. I didn't let him know it, for I knew that the plane I had let get away would guide a party here and I thought I might be able to help out. When you came and attacked the house, I worked at my bonds until they were loose enough to throw off. I saw Koskoff start my cold apparatus to working and then he quit, because he ran out of helium. When he started shooting again, I worked out of my bonds and tackled him.
"He was a better man than I gave him credit for, or else he suspected me, for about the time I grabbed him he whirled and struck me over the head with his gun barrel and tore my face open. The blow stunned me, and when I came to, I was thrown into this corner. I meant to have another try at it, but I guess you rushed him too fast. He turned and ran for the tunnel, but as he did so, he shot me through the body. I guess I didn't look dead enough to suit him. You gentlemen broke open the door and came in. That's all."
"Not by a long shot, it isn't," exclaimed Dr. Bird. "Where is that cold light apparatus of yours?"
"In the tunnel."
"How do you get into it?"
"If you will open that cupboard on the wall, you'll find an open knife switch on the wall. Close it."
Dr. Bird found the switch and closed it. As he did so the cabin rocked on its foundations and both Carnes and Walter were thrown to the ground. The thud of a detonation deep in the earth came to their ears.
"What was that?" cried the doctor.
"That," replied Smith with a wan smile, "was the detonation of two hundred pounds of T.N.T. When you dig down into the underground cave where we used the cold light apparatus, you will find it in fragments. It was my only child, and I'll take it with me."
As he finished his head slumped forward on his chest. With an exclamation of dismay Dr. Bird sprang forward and tried to lift the prostrate form.