The trouble was that he could do very little more here than he could in the tractor. He could have improvised longer-wave transmitting coils whose radiations would have diffracted a little more effectively beyond the horizon, but the receiver on the missing vehicle would not have detected them. He had more power at his disposal, but could only beam it into empty space with his better antennae. He had better equipment for locating any projecting wisps of charged gas which might reflect his waves, but he was already located under a solid roof of the stuff--the _Albireo_ was technically on Brightside. Bouncing his beam from this layer still didn't give him the range he needed, as he had found both by calculation and trial. What he really needed was a relay satellite. The target was simply too far around Mercury's sharp curve by now for anything less. Zaino's final gesture was to set his transmission beam on the lowest frequency the tractor would pick up, aim it as close to the vehicle's direction as he could calculate from map and itinerary and set the recorded return message going. He told Rowson as much. "Can't think of anything else?" the captain asked. "Well, neither can I, but of course it's not my field. I'd give a year's pay if I could. How long before they should be back in range?" "About four days. A hundred hours, give or take a few. They'll be heading back anyway by that time." "Of course. Well, keep trying." "I am--or rather, the equipment is. I don't see what else I can do unless a really bright idea should suddenly sprout. Is there anywhere else I could be useful? I'm as likely to have ideas working as just sitting." "We can keep you busy, all right. But how about taking a transmitter up one of those mountains? That would get your wave farther." "Not as far as it's going already. I'm bouncing it off the ion layer, which is higher than any mountain we've seen on Mercury even if it's nowhere near as high as Earth's." "Hmph. All right." "I could help Ren and Dr. Burkett. I could hang on outside the tractor--" "They've already gone. You'd better call them, though, and keep a log of what they do." "All right." Zaino turned back to his board and with no trouble raised the tractor carrying Hargedon and the mineralogist. The latter had been trying to call the _Albireo_ and had some acid comments about radio operators who slept on the job. * * * * * "There's only one of me, and I've been trying to get the Darkside team," he pointed out. "Have you found anything new about this lava flood?"