"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 glass would do so, but I have a camera here equipped with a rock crystal lens, which will allow ultra-violet light to pass 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."