 How did the Mercurians adjust to the heat?
Only the native waiters, the enigmatic, yellow-eyed Mercurians, seemed unaffected by the heat. The revolution is scheduled to break during the Festival of the Rains. Jaro Moynahan wiped the sweat from his forehead with a fine duraweb handkerchief. The Mercurians worship him. Jaro Moynahan refilled their empty glasses. "Ah," said Jaro Moynahan; "so that's the way it is." One moment the garden was glowing in light, the next the hot black night swooped down on the revelers, pressing against their eyes like dark wool. Across the table from Jaro there was the feel of movement; he could sense it. On the hot, teeming planet of Mercury it was as refreshing as a cold plunge. These yellow-eyed Mercurians could see as well in the dark as any alley-prowling cat. For centuries they had lived most their lives beneath ground to escape the terrible rays of the sun. Only at night did they emerge to work their fields and ply their trades. If the girl had been abducted, only Mercurians could have engineered it in the dark; and the Mercurians were a clannish lot. By stretching out his arms he could touch the buildings on either side: buildings with walls four feet thick to keep out the heat of the sun. They were never visible, but to his trained ears there came stealthy, revealing noises: the brush of cloth against the baked earth walls, the sly shuffle of a step. In the dense, humid night, he was like a blind man trying to elude the cat-eyed Mercurians. Jaro Moynahan In the East a sullen red glow stained the heavens like the reflection of a fire. The Mercurian dawn was about to break. Once back in his room, Jaro Moynahan stripped off his clothes, unbuckled a shoulder holster containing a compressed air slug gun, stepped under the shower. He had fought in the deadly little wars of the Moons of Jupiter for years, then the Universal Debacle of 3368, after that the Martian Revolution as well as dozens of skirmishes between the Federated Venusian States. The Mercurians, he knew, had been agitating for freedom for years. Why, at this time when the Earth Congress was about to grant them self-government, should they stage a revolution? Unless Karfial Hodes is stopped immediately there will be a bloody uprising all over the planet during the Festival of the Rains. Earth doesn't realize the seriousness of the situation." "There are many of us here, Mercurians as well as Earthmen, who recognize the danger.
 They mostly lived under the ground.
 Their yellow eyes filtered the sun’s rays.  They mostly lived under the ground.  Their skin kept them cool.  They would sweat to cool off.