Powell’s eyes swept the jagged glitter of Mercury to the horizon and winced at the gorgeous brilliance.

“This must be an unusual area,” he said. “The general albedo of Mercury is low and most of the soil is gray pumice. Something like the Moon, you know. Beautiful, isn’t it?”

He was thankful for the light filters in their visiplates. Beautiful or not, a look at the sunlight through straight glass would have blinded them inside of half a minute.

Donovan was looking at the spring thermometer on his wrist. “Holy smokes, the temperature is eighty centigrade!”

Powell checked his own and said: “Um-m-m. A little high. Atmosphere, you know.”

“On Mercury? Are you nuts?”

“Mercury isn’t really airless,” explained Powell, in absentminded fashion. He was adjusting the binocular attachments to his visiplate, and the bloated fingers of the insosuit were clumsy at it. “There is a thin exhalation that clings to its surface—vapors of the more volatile elements and compounds that are heavy enough for Mercurian gravity to retain. You know: selenium, iodine, mercury, gallium, potassium, bismuth, volatile oxides. The vapors sweep into the shadows and condense, giving up heat. It’s a sort of gigantic still. In fact, if you use your flash, you’ll probably find that the side of the cliff is covered with, say, hoar-sulphur, or maybe quick-silver dew.

“It doesn’t matter, though. Our suits can stand a measly eighty indefinitely.”

Powell had adjusted the binocular attachments, so that he seemed as eye-stalked as a snail.

Donovan watched tensely. “See anything?”

The other did not answer immediately, and when he did, his voice was anxious and thoughtful. “There’s a dark spot on the horizon that might be the selenium pool. It’s in the right place. But I don’t see Speedy.”

Powell clambered upward in an instinctive striving for better view, till he was standing in unsteady fashion upon his robot’s shoulders. Legs straddled wide, eyes straining, he said: “I think… I think— Yes, it’s definitely he. He’s coming this way.”

Donovan followed the pointing finger. He had no binoculars, but there was a tiny moving dot, black against the blazing brilliance of the crystalline ground.

“I see him,” he yelled. “Let’s get going!”

Powell had hopped down into a sitting position on the robot again, and his suited hand slapped against the Gargantuan’s barrel chest. “Get going!”

“Giddy-ap,” yelled Donovan, and thumped his heels, spur fashion.

The robots started off, the regular thudding of their footsteps silent in the airlessness, for the nonmetallic fabric of the insosuits did not transmit sound. There was only a rhythmic vibration just below the border of actual hearing.

“Faster,” yelled Donovan. The rhythm did not change.

“No use,” cried Powell, in reply. “These junk heaps are only geared to one speed. Do you think they’re equipped with selective flexors?”

They had burst through the shadow, and the sunlight came down in a white-hot wash and poured liquidly about them.

Donovan ducked involuntarily. “Wow! Is it imagination or do I feel heat?”

“You’ll feel more presently,” was the grim reply. “Keep your eye on Speedy.”