somewhere on Venus, close beneath this location," Curt persisted. "We'll have to find them."
The Comet dived sharply through the gray, swirling vapors. The ion trail had long ago been dispersed here, of course, but the ship of the Futuremen sank down through mile after mile of the cloudy atmosphere.
"Venus' atmosphere is far thicker and denser than in our own time, lad," commented the Brain. "The planet's hydrosphere has not yet condensed so much into surface water as in our own age."
They emerged at last into the stratum of clear air close to the surface of the planet. Astonished, they looked across a vista of parklike fields and glades, fringed by a belt of marsh near the ocean.
"But where are all the great swamps of Venus?" demanded Grag, staring.
"It's just as I said," reminded the Brain. "The hydrosphere vapors have not yet condensed enough to saturate the planet with water and make it the swampy world we know. The process, though, is steadily going on."
There began again a weary process of search. The Comet circled in widening spirals above the land beneath. Three superhuman pairs of eyes kept peering for the strange black space ship they were hunting. While they saw nothing of the ship, they did notice stone structures and cities, submerged far out in the ocean, or partly concealed by the coastal marshes.
"There's been a civilization here on Venus, too," said the Brain, "just as on Earth. Just as the glaciation on Earth wrecked that civilization, so has it been destroyed here by the steady rise of the waters."
"I can't make it out," complained Grag. "Who'd have dreamt these worlds had great civilizations on them even longer ago than this?"
"There seem to be still greater ruined cities submerged far out in the sea," reported the Brain, who was peering through instruments. "The nearer the ruins are to shore, the smaller they become. It looks as though the steady rise of the water forced the people out of one city after another, bringing about a gradual retrogression of their civilization."
Curt Newton was too concerned with the search for Otho's captors to give this astonishing fact the attention he would ordinarily have given.
His keen eyes presently descried human figures moving over a field. He sent the Comet diving down toward them. The men appeared to be a hunting party, armed with throwing spears and bows. They were a white-skinned folk of apparently the same stage of primitive culture as the tribesmen on Earth. They bolted in flight the instant they heard and saw the Comet.
"Shall we land and catch some of 'em for questioning?" Grag asked.
"It would be wasting time," Curt said. "They're just primitive descendants of a once-great people. They wouldn't be likely to have any connection with Otho's captors, who must be a fairly civilized people."
"Doesn't look like there are any civilized people on this world," Grag asserted. "The ones who captured Otho couldn't have come from here."
"I'm beginning to think that myself," Curt admitted. His brows knitted together. "Maybe they just stopped here at Venus for some reason and then went on. Let's go out into space and see if we can find their trail."
The Comet roared up through the immense cloudy envelope of the planet and emerged into clear, star-jeweled space. Curt and Simon began once more to sweep space with the powerful electroscope. Again it took weary hours of circling through space before they located a different ion trail than the one they had followed into Venus.
"They did stop at Venus and then go on!" Curt cried. "See? This trail leads out toward Mars."
"Do you think the people who captured Otho and Ahla are Martians?" Grag questioned. Without waiting for an answer, he growled; "What a chase that silly android is leading us!"
THE Comet shot toward the fourth planet with all cycs and tubes throbbing. Captain Future knew that their delay at Venus had again given those they pursued a large lead. He looked worriedly beyond Mars to the distant