There was something very queer about it all.  “Strange that we should see no movement in those clouds,” mused the doctor aloud.  “That is, if they really are clouds.”

Van Emmon already doubted it.  “Just what I was thinking.  There ought to be terrific winds; yet, so far as I have seen, there’s been nothing doing anywhere on the surface since we first began to observe it.”

After a while the doctor put away his binoculars and rubbed his eyes.  “We might as well descend faster, Smith.  Can’t see a thing from here.”

Unhindered by air to impede its progress the sky-car had been hurtling through space at cometary speed.  Now, however, Smith added the power of the apparatus to the pull of the planet, so that the disk began to rush toward them at a truly alarming rate.  After a few seconds of it Billie found herself unconsciously moving to the side of the geologist.

He looked down at her, understood, and flushed with pleasure.  “There’s no danger,” he confidently assured her, with the result that, her courage fortified, the girl moved back to her place again.  Van Emmon inwardly kicked himself.

So deceptive was that peculiar fogginess Smith throttled their descent as soon as they had reached the point where the planet’s appearance changed from round to flat.  They were headed for the line which marked the boundary of the shadow.  This gray “twilight zone” was three or four hundred miles in width; on the right of it—­to the east—­the dazzling surface of that sunlit vapor contrasted sharply with the all but black mistiness of the starward side.  Clearly the zone ought to be temperate enough.

Down they sank.  As they came nearer a curious pinkish tint began to show beneath them.  Shortly it became more noticeable; the doctor gave a sudden grunt of satisfaction, and Smith stopped the car.

A minute later the doctor had taken a sample of the surrounding ether through his laboratory test-vestibule; and shortly announced that they were now floating in air instead of space.

“Good deal like ours back home, too”—­exultingly.  “Pretty thin, of course.”  He made a short calculation, referring to the aneroid barometer which was mounted on the outer frame of a window, and said he judged that their altitude was about five miles.

The descent continued, Smith using the utmost caution.  The other three kept their eyes glued to the deadlight; and their mystification was only equaled by their uneasiness as that motionless, bleary glaze failed absolutely to show anything they had not seen a thousand miles higher.  Not a single detail!

“It reminds me,” said the girl in a low voice, “of something I once saw from the top of a hill.  It was the reflection of the sun from the surface of a pond; not clear water, but covered with—­”

“Good Heavens!” interrupted Van Emmon, struck with the thought.  “Can it be that the whole planet is under water?”