He took a transit-like instrument from the case, pulled out the legs of its self-contained tripod, then carried it to a spot near where he had estimated the first charge would be placed. The instrument was equipped with three movable rings to be set for the celestial equator, for the zero meridian, and for the right ascension of any convenient star. Using a regular level would have been much simpler. The instrument had one, but with so little gravity to activate it, the thing was useless. The sights were specially designed for use in space and his bubble was no obstacle in taking observations. He merely put the clear plastic against the curved sight and looked into it much as he would have looked through a telescope on earth. As he did so, a hint of pale pink light caught the corner of his eye. He backed away from the instrument and turned his head quickly, looking at the colorimeter-type radiation detector at the side of his helmet. It was glowing. An icy chill sent a shiver through him. Great, gorgeous galaxies! He had forgotten ... had Koa and the others? He turned so fast he lost balance and floated above the surface like a captive balloon. Santos, who had been standing near by to help if requested, hooked a toe on a ground spike, caught him, and set him upright on the ground again. "Get me the radiation detection instruments," he ordered. Koa sensed the urgency in his voice and got the instruments himself. Rip switched them on and read the illuminated dial on the alpha counter. Plenty high, as was natural. But no danger there—alpha particles couldn’t penetrate the space suits. Then, his hand clammy inside the space glove, he switched on the other meter. The gamma count was far below the alpha, but there were too many of the rays around for comfort. Inside the helmet, his face turned pale. There was no immediate danger. It would take many days to build up a dose of gamma that could hurt them. But gamma was not the only radiation. They were in space, fully exposed to equally dangerous cosmic radiation. The Planeteers had gathered while he read the instruments. Now they stood watching him. They knew the significance of what he had found. "I ought to be busted to recruit," he told them. "I knew this asteroid was thorium, and that thorium is radioactive. If I had used my head, I would have added nuclite shielding to the list of supplies the _Scorpius_ provided. We could have had enough of it to protect us while around our base, even if we couldn’t be protected while working on the charges. That would at least have kept our dosage down enough for safety." "No one else thought of it, either, sir," Koa reminded. "It was my job to think of it, and I didn’t. So I’ve put us in a time squeeze. If the _Scorpius_ gets back soon, we can get the shielding before our radiation dosage has built up very high. If the ship doesn’t come back, the dosage will mount."