"The human eye cannot detect ultra-violet. Suppose then, that we have an object, either animate or inanimate, the surface of which reflects only ultra-violet light, what will be the result? The object will be invisible."
"I should think it would be black if all the rays except the ultra-violet were absorbed."
"It would, but mark, I did not say the others were absorbed. Are you familiar with fluorescein?"
"No."
"I think you are. It is the dye used in making changeable silk. If we fill a gla.s.s container with a fluorescein solution and look at it by reflected light it appears green. If we look at it by transmitted light, that is, light which has traversed the solution, it appears red. In other words, this is a substance which reflects green light, allows a free pa.s.sage to red light, and absorbs all other light. This creature we are after, if my theory is correct, is composed of a substance which allows free pa.s.sage to all of the visible light rays and at the same time reflects ultra-violet light. Do I make this clear?"
"Perfectly."
"Very well, then. My apparatus will project forward a beam of ultra-violet light which will be in much greater concentration than exists in an incandescent electric light. It is my hope that this light will be reflected by the body of the creature to a sufficient to allow me to make a photograph of it."
"But won"t your lens prevent the ultra-violet light from reaching your plate?"
"An ordinary lens made of optical gla.s.s would do so, but I have a camera here equipped with a rock crystal lens, which will allow ultra-violet light to pa.s.s through it practically unhindered, and with very slight distortion. When I add that I will have my camera charged with X-ray film, a film which is peculiarly sensitive to the shorter wave-lengths, you will see that I will have a fair chance of success."
"It sounds logical. Would you allow me to accompany you when you make your attempt?"
"I will be glad of your company, if you can drive a tank. I want to take Carnes with me, and the tank will only hold two besides the driver."
"I can drive a tractor."
"In that case you should master the tricks of tank driving in short order. Get familiar with it and we"ll appoint you as driver. We"ll be ready to go in to-night, but I am going to wait a day. Our friend was fed last night, and there is less chance he"ll be about."
The early part of the next evening was marked by howls and screams coming from the mouth of the cave. As the night wore on the noises were quite evidently coming nearer and the sentries watched the cave mouth nervously, ready to bolt and scatter according to their orders at the first alarm. About two A. M. the doctor and Carnes climbed into the tank beside Lieutenant Leffingwell, and the machine moved slowly into the cave. A search-light on the front of the tank lighted the way for them and, attached to a frame which held it some distance ahead of them, was a luckless sheep.
"Keep your eye on the mutton, Carnes," cautioned the doctor. "As soon as anything happens to it, shut off the search-light and let me try to get a picture. As soon as I have made my exposures I"ll tell you, and you can snap it on again. Lieutenant, when the picture is made, turn your tank and make for the entrance to the cave. If we are lucky, we"ll get out."
Forward the tank crawled, the sheep bleating and trying to break loose from the bonds which held it. It was impossible to hear much over the roar of the motor, but presently Dr. Bird leaned forward, his eyes shining.
"I smell musk," he announced. "Get ready for action."
Even as he spoke the sheep was suddenly lifted into the air. It gave a final bleat of terror, and then its head was torn from its body.
"Quick, Carnes!" shouted the doctor.
The search-light went out, and Carnes and the lieutenant could hear the slide of the ultra-violet light which Dr. Bird was manipulating open. For two or three minutes the doctor worked with his apparatus.
"All right!" he cried suddenly. "Lights on and get out of here!"
Carnes snapped on the search-light and Lieutenant Leffingwell swung the tank around and headed for the cave mouth. For a few feet their progress was unhindered and then the tank ceased its forward motion, although the motor still roared and the track slid on the cave floor. Carnes watched with horror as one side of the tank bent slowly in toward him. There was a rending sound, and a portion of the heavy steel fabric was torn away. Dr. Bird bent over something on the floor of the tank. Presently he straightened up and threw a small object into the darkness. There was a flash of light, and bits of flaming phosphorus flew in every direction. The anchor which held the tank was suddenly loosed and the machine crawled forward at full speed, while a roar as of escaping air mingled with a bellowing shriek burdened the smoke-laden air.
"Faster!" cried the doctor, as he threw another grenade.
Lieutenant Leffingwell got the last bit of speed possible out of the tank and they reached the cave mouth without further molestation.
"I had an idea that our friend wouldn"t care to pa.s.s through a phosphorus screen," said Dr. Bird with a chuckle as he climbed out of the tank. "He must have been rather severely burned the other day, and once burned is usually twice shy. Where is Major Brown?"
The commanding officer stepped forward.
"Drive a couple of cattle into the cave, Major," directed Dr. Bird. "I want to fill that brute up and keep him quiet for a while. I"m going to develope my films."
Lieutenant Leffingwell and Carnes peered over the doctor"s shoulders as he manipulated his films in a developing bath. Gradually vague lines and blotches made their appearance on one of the films, but the form was indistinct. Dr. Bird dropped the films in a fixing tank and straightened up.
"We have something, gentlemen," he announced, "but I can"t tell yet how clear it is. It will take those films fifteen minutes to fix, and then we"ll know."
In a quarter of an hour he lifted the first film from the tank and held it to the light. The film showed a blank. With an exclamation of disappointment he lifted a second and third film from the tank, with the same result He raised the fourth one.
"Good Lord!" gasped Carnes.
In the plate could be plainly seen the hind quarters of the sheep held in the grasp of such a monster as even the drug-laden brain of an opium smoker never pictured. Judging from the sheep, the monster stood about twenty feet tall, and its frame was surmounted by a head resembling an overgrown frog. Enormous jaws were opened to seize the sheep but, to the amazement of the three observers, the jaws were entirely toothless. Where teeth were to be expected, long parallel ridges of what looked like bare bone, appeared, without even a rudimentary segregation into teeth. The body of the monster was long and snakelike, and was borne on long, heavy legs ending in feet with three long toes, armed with vicious claws. The crowning horror of the creature was its forelegs. There were of enormous length, thin and attenuated looking, and ended in huge misshapen hands, k.n.o.bby and blotched, which grasped the sheep in the same manner as human hands. The eyes were as large as dinner plates, and they were glaring at the camera with an expression of fiendish malevolence which made Carnes shudder.
"How does that huge thing ever get through that crack we examined?" demanded the lieutenant.
Dr. Bird rubbed his head thoughtfully.
"It"s not an amphibian," he muttered, "as is plainly shown by the shape of the limbs and the lack of a tail, and yet it appears to have scales of the true fish type. It corresponds to no recovered fossil, and I am inclined to believe it is unique. The nervous organisation must be very low, judging from the lack of forehead and the general conformation. It has enormous strength, and yet the arms look feeble."
"It can"t get through that crack," insisted the lieutenant.
"Apparently not," replied the doctor. "Wait a moment, though. Look at this!"
He pointed to the great disproportion between the length and diameter of the forelegs, and then to the hind legs.
"Either this is grave distortion or there is something mighty queer about that conformation. No animal could be constructed like that."
He turned the film so that an oblique light fell on it. As he did so he gave a cry of astonishment.
"Look here!" he said sharply. "It does get through that crack! Look at those arms and hands! There is the answer. This creature is tall and broad, but from front to rear it can measure only a few inches. The same must be true of the froglike head. That animal has been developed to live and move in a low roofed cavern, and to pa.s.s through openings only a few inches wide. Its bulk is all in two dimensions!"
"I believe you"re right," said Carnes as he studied the film.
"There is no doubt of it," answered the doctor. "Look at those paws, too, Carnes. That substance isn"t bone, it"s gum. The thing is so young and helpless that it hasn"t cut its teeth yet. It must be a baby, and that is the reason why it made its way into the cave when no other of its kind ever has."
"How large are full grown ones if this is a baby?" asked the lieutenant.
"The Lord alone knows," replied Dr. Bird. "I hope that I never have to face one and find out. Well, now that we know what we are fighting, we ought to be able to settle its hash."
"High explosive?" suggested the lieutenant.
"I don"t think so. With such a low nervous organization, we would have to tear it practically to pieces to kill it, and I am anxious to keep it from mutilation for scientific study. I have an idea, but I"ll have to study a while before I am sure of the details. Send me the radio operator."
The next day the Bureau mechanics began to dismount the apparatus from the tank and to a.s.semble another elaborate contrivance. Before they had made an end of the work additional equipment arrived from Washington, which was incorporated in the new set-up. At length Dr. Bird p.r.o.nounced himself ready for the attempt.
Under his direction, three cattle were driven into the cave and there tethered. They were there the next morning unharmed, but the second night the now familiar bellowing and howling came from the depths of the cave and in the morning two of the cattle were gone.
"That will keep him quiet for a day or two," said the doctor, "and now to work!"