"Good! As soon as we can get them we"ll start. In the meantime, may I look at that gun that was found?"
The Browning machine-gun was laid before the doctor. He looked it over critically and sniffed delicately at it. He took from his pocket a phial of liquid, moistened a portion of the water-jacket of the weapon, and then rubbed the moistened part briskly with his hand. He sniffed again. He looked disappointed, and again examined the gun closely.
"Carnes," he said at length, "do you see anything on this gun that looks like tooth marks?"
"Nothing, Doctor."
"Neither do I. There are some marks here which might quite conceivably be finger-prints of a forty-foot giant, and those two parallel grooves look like the result of severe squeezing, but there are no tooth marks. Strange. There is no persistent odor on the gun, which is also strange. Well, there"s no use in theorizing: we are confronted by a condition and not a theory, as someone once said. Let"s put on those baseball shoes and see what we can find out."
Dr. Bird led the way into the cave, Carnes and the lieutenant following closely with electric torches. In each hand Dr. Bird carried a phosphorus hand-grenade. No other weapons were visible, although the doctor knew that Carnes carried a caliber .45 automatic pistol strapped under his left armpit. As they pa.s.sed into the cave the lieutenant stepped forward to lead the way.
"I"m going first," said the doctor. "Follow me and indicate the turns by pressure on my shoulder. Don"t speak after we have started, and be ready for instant flight. Let"s go."
Forward into the interior of the cave they made their way. The iron cleats of the baseball shoes rang on the floor and the noise echoed back and forth between the walls, dying out in little eerie whispers of sound that made Carnes" hair rise. Ever forward they pressed, the lieutenant guiding the doctor by silent pressure on his shoulder and Carnes following closely. For half a mile they went on until a restrainable pressure brought the doctor to a halt. The lieutenant pointed silently toward a crack in the wall before them. Carnes started forward to examine it, but a warning gesture from the doctor stopped him.
Slowly, an inch at a time, the doctor crept forward, hand-grenades in readiness. Presently he reached the crack and, shifting one of the grenades into his pocket, he drew forth an electric torch and sent a beam of light through the crack into the dark interior of the earth.
For a moment he stood thus, and then suddenly snapped off his torch and straightened up in an att.i.tude of listening. The straining ears of Carnes and Lieutenant Pearce could hear a faint slithering noise coming toward them, not from the direction of the crack, but from the interior of the cave. Simultaneously a faint, musky, reptilian odor became apparent.
"Run!" shouted the doctor. "Run like h.e.l.l! It"s loose in the cave!"
The lieutenant turned and fled at top speed toward the distant entrance to the cave, Carnes at his heels. Dr. Bird paused for an instant, straining his ears, and then threw a grenade. A blinding flash came from the point where the missile struck and a white cloud rose in the air. The doctor turned and fled after his companions. Not for nothing had Dr. Bird been an athlete of note in his college days. Despite the best efforts of his companions, who were literally running for their lives, he soon caught up with them. As he did so a weird, blood-curdling screech rose from the darkness behind them. Higher and higher in pitch the note rose until it ended suddenly in a gurgling grunt, as though the breath which uttered it had been suddenly cut off. The slithering, rustling noise became louder on their trail.
"Faster!" gasped the doctor, as he put his hand on Carnes" shoulder and pushed him forward.
The noise of pursuit gained slightly on them, and a sound as of intense breathing became audible. Dr. Bird paused and turned and faced the oncoming horror. His electric torch revealed nothing, but he listened for a moment, and then threw his second grenade. Keenly he watched its flight. It flew through the air for thirty yards and then struck an invisible obstruction and bounded toward the ground. Before it struck the downward motion ceased, and it rose in the air. As it rose it burst with a sharp report, and a wild scream of pain filled the cavern with a deafening roar. The doctor fled again after his companions.
By the time he overtook them the entrance of the cave loomed before them. With sobs of relief they burst out into the open. The guards sprang forward with raised rifles, but Dr. Bird waved them back.
"There"s nothing after us, men," he panted. "We got chased a little way, but I tossed our pursuer a handful of phosphorus and it must have burned his fingers a little, judging from the racket he made. At any rate, it stopped the pursuit."
The major hurried up.
"Did you see it, Doctor?" he asked.
"No, I didn"t. No one has ever seen it or anything like it. I heard it and, from its voice, I think it has a bad cold. At least, it sounded hoa.r.s.e, so I gave is a little white phosphorus to make a poultice for its throat, but I didn"t get a glimpse of it."
"For G.o.d"s sake, Doctor, what is it?"
"I can"t tell you yet, Major. So far I can tell, it is something new to science and I am not sure just what it looks like. However, I hope to be able to show it to you shortly. Is there a telegraph office here?"
"No, but we have a Signal Corps detachment with us, and they have a portable radio set which will put us in touch with the army net."
"Good! Can you place a tent at my disposal?"
"Certainly, Doctor."
"All right, I"ll go there, and I would appreciate it if you would send the radio operator to me. I want to send a message to the Bureau of Standards to forward me some apparatus which I need."
"I"ll attend to it, Doctor. Have you any special advice to give me about the guarding?"
"Yes. Have you, or can you get, any live stock?"
"Live stock?"
"Yes. Cattle preferred, although hogs or sheep will do at a pinch. Sheep will do quite well."
"I"ll see what I can do, Doctor."
"Get them by all means, if it is possible to do so. Don"t worry about paying for them: secret service funds are not subject to the same audit that army funds get. If you can locate them, drive a couple of cattle or half a dozen sheep well into the cave and tether them there. If you don"t get them, have your sentries posted well away from the cave mouth, and if any disturbance occurs during the night, tell them to break and run. I hope it won"t come out, but I can"t tell."
A herd of cattle was soon located and two of the beasts driven into the cave. Two hours later a series of horrible screams and bellowings were heard in the cave. Following their orders the sentries abandoned their posts and scattered, but the noise came no nearer the mouth, and in a few minutes silence again reigned.
"I hope that will be all that will be needed for a couple of days," said the doctor to the commanding officer, "but you had better have a couple more cattle driven in in the morning. We want to keep the brute well fed. Is there a tank stationed at Fort Thomas?"
"No, there isn"t."
"Then radio Washington that I want the fastest three-man tank that the army has sent here at once. Don"t bother with military channels, radio direct to the Adjutant General, quoting the Secretary of the Treasury as authority. Tell him that it"s a rush matter, and sign the message "Bird" if you are afraid of getting your tail twisted."
Twice more before the apparatus which the doctor had ordered from Washington arrived cattle were driven into the depths of the cave, and twice were the screams and bellowings from the cave repeated. Each time searching parties found the cattle gone in the morning. A week after the doctor"s arrival, a special train came up, carrying four mechanics from the Bureau of Standards, together with a dozen huge packing cases. Under the direction of the doctor the cases were unpacked and the apparatus put together. Before the a.s.sembly had been completed the tank which had been requested arrived from Camp Meade, and the Bureau mechanics began to install some of the a.s.sembled units in it.
The first apparatus which was installed in the tank consisted of an electric generator of peculiar design which was geared to the tank motor. The electromotive force thus generated was led across a spark gap with points of a metallic substance. The light produced was concentrated by a series of parabolic reflectors, directed against a large quartz prism, and thence through a lens which was designed to throw a slightly divergent beam.
"This apparatus," Dr. Bird explained to the Signal Corps officer, who was an interested observer, "is one which was designed at the Bureau for the large scale production of ultra-violet light. There is nothing special about the generator except that it is highly efficient and gives an almost constant electromotive force. The current thus produced is led across these points, which are composed of magnalloy, a development of the Bureau. We found on investigation that a spark gave out a light which was peculiarly rich in ultra-violet rays when it was pa.s.sed between magnesium points. However, such points could not be used for the handling of a steady current because of lack of durability and ease of fusion, so a mixture of graphite, alundum and metallic magnesium was pressed together with a binder which will stand the heat. Thus we get the triple advantages of ultra-violet light production, durability, and high resistance.
"The system of reflectors catches all of the light thus produced except the relatively small portion which goes initially in the right direction, and directs it on this quartz prism where, due to the refractive powers of the prism, the light is broken up into its component parts. The infra-red rays and that portion of the spectrum which lies in the visible range, that is, from red to violet inclusive, are absorbed by a black body, leaving only the ultra-violet portion free to send a beam through this quartz lens."
"I thought that a lens would absorb ultra-violet light," objected the signal officer.
"A lens made of gla.s.s will, but this lens is made of rock crystal, which is readily permeable to ultra-violet. The net result of this apparatus is that we can direct before us as we move in the tank a beam of light which is composed solely of the ultra-violet portion of the spectrum."
"In other words, an invisible light?"
"Yes. That is, invisible to the human eye. The effect of this beam of ultra-violet light in the form of severe sunburn would be readily apparent if you exposed your skin to it for any length of time, and the effects on your eyesight of continued gazing would be apt to be disastrous. It would produce a severe opthalmia and temporary impairment of the vision, somewhat the same symptoms as are observed in snow blindness."
"I see. May I ask what is the object of the whole thing?"
"Surely. Before we can successfully combat this peculiar visitant from another world, it is necessary that we gain some idea of the size and appearance of it. Nothing of the sort has before made its appearance, so far as the annals of science go, and so I am forced to make some rather wild guesses at the nature of the animal. You are probably aware of the fact that the property of penetration possessed by all waves is a function of their frequency, or, perhaps I should say, of their wave-length?"
"Certainly."
"The longer rays of visible light will not penetrate as deeply into a given substance as the shorter ultra-violet rays. This visitor is evidently from some unexplored and, indeed, unknown cavern in the depths of the earth where visible light has never penetrated. Apparently in this cavern the color of the inhabitants is ultra-violet, and hence invisible to us."
"You are beyond my depth, Doctor."
"Pardon me. You understand, of course, what color is? When sunlight, which is a mixture of all colors from infra-red to ultra-violet inclusive, falls oh an object, certain rays are reflected and certain others are absorbed. If the red rays are reflected and all others absorbed, the object appears red to our eyes. If all the rays are reflected, the object appears white, and if all are absorbed, it appears black."
"I understand that."