The guides consulted a moment and started out. Carnes drove up the burro the Doctor had indicated and Dr. Bird unpacked it. He opened a mahogony case and took from it a high powered microscope. Setting the instrument up on a convenient rock, he subjected portions of the wreck, including several fragments of flesh, to a careful scrutiny. When he had completed his observations he fell into a brown study, from which he was aroused by Carnes. "What did you find out about the cause of the wreck, Doctor?" "I don't know what to think. The immediate cause was that everything was frozen. The plane ran into a belt of cold which froze up the motor and which probably killed the crew instantly. It was undoubtedly the aftermath of that cold which you felt when you swooped down over the wreck." "It seems impossible that it could have suddenly got cold enough to freeze everything up like that." "It does, and yet I am confident that that is what happened. It was no ordinary cold, Carnes; it was cold of the type that infests interstellar space; cold beyond any conception you have of cold, cold near the range of the absolute zero of temperature, nearly four hundred and fifty degrees below zero on the Fahrenheit scale. At such temperatures, things which are ordinarily quite flexible and elastic, such as rubber, or flesh, become as brittle as glass and would break in the manner which these bodies have broken. An examination of the tissues of the flesh shows that it has been submitted to some temperature that is very low in the scale, probably below that of liquid air. Such a temperature would produce instant death and the other phenomena which we can observe." "What could cause such a low temperature, Doctor?" "I don't know yet, although I hope to find out before we are finished. Cold is a funny thing, Carnes. Ordinarily it is considered as simply the absence of heat; and yet I have always held it to be a definite negative quantity. All through nature we observe that every force has its opposite or negative force to oppose it. We have positive and negative electrical charges, positive and negative, or north and south, magnetic poles. We have gravity and its opposite apergy, and I believe cold is really negative heat." "I never heard of anything like that, Doctor. I always thought that things were cold because heat was taken from them--not because cold was added. It sounds preposterous." * * * * * "Such is the common idea, and yet I cannot accept it, for it does not explain all the recorded phenomena. You are familiar with a searchlight, are you not?" "In a general way, yes."