He drew up his plans this time with sureness. He was no longer amazed at the progress he'd made in understanding extraspectral phenomena. It might very well represent the work of generations of scientists, but he was a robot designed to understand human science, even from the few smatterings the Aliens had been able to learn before he had been created. He finished the designs, wrote down the proper formulae, and stacked the paper in front of the television pick-up, pressing the call button. Without waiting for an answer, he went back into the workshop, and began assembling the tiny, radio-active strontium batteries and tubes of protein plastic, wound with layers of iron wire. He had enough for what he needed. The device was set to work both as a detector and a generator of the radiation involved. He tuned one, setting it to receive. It took a few minutes to replace the antenna of the small radar set with the new device, and he forced himself to work faster by the sheer drive of his will. Then he stepped aside, letting mechanism revolve on the antenna mount. He began increasing the current that controlled the degree of electromagnetism in the wire which served to tune the device. A pip appeared on the screen, pointing toward the cage where the male and crippled female lay peacefully together. Norden raised the frequency until another pip appeared, this time pointing to the rabbits. He adjusted it for maximum brightness. In the section which should cover the direction of Moon base below him, a brilliant glow sprang up, indicating radiation that cut straight through all the layers of the Moon. He adjusted the instrument again. He found the exact frequency, and the whole screen suddenly blazed, blanked out by overloading of the amplifier. Apparently all life of terrestrial origin radiated at the same frequency. He cranked up the control, expecting nothing more. Then he bent sharply forward as other pips appeared, indicating objects far out in space! The Aliens also radiated in the same spectrum--but at such an incredibly high frequency that no atomic nucleus was small enough to be affected by the radiation. As Norden watched, the central pip suddenly began to grow brighter, holding its position in a way that indicated a straight descent toward his detector! Terror struck at his nerves. Obviously the Aliens had detectors for every frequency, and his detector was just crude enough to radiate a faint trace of its own. He'd been located, and the exterminating force was on the way. VII Norden cursed his own stupidity, and estimated the time it would take. If they decided to come in, and spray the area with their own force, or to capture it, he had several minutes. If they sent one of their super-speed torpedoes, he was on borrowed time. His mind raced furiously.