Beyond a doubt his guess was justified.  There was an oily smoothness about that dazzling haze which made it remarkably like a lake of still and rather dirty water under a bright sun.

But the doctor said no.  “Any water I ever heard of would make clouds,” said he; “and we know there’s air enough to guarantee plenty of wind.  Yet nothing seems to be in motion.”  He was frowning continually now.

It was Billie who first declared that she saw the surface.  “Stop,” she said to Smith evenly, and he instantly obeyed.  All four gathered around the deadlight, and soon agreed that the peculiarly elusive skin of the planet was actually within sight.  However, it was like deciding upon the distance of the moon—­as easy to say that it were within arm’s reach as a long ways off.

The doctor went to a window.  There he could look out upon the sun, a painfully bright object much larger than it looks from the Earth.  It was just “ascending,” and half of it was below the horizon.  A blinding streak of light was reflected from a point on the surface not far from the cube.  Shading his eyes with his hand the doctor could see that the mysterious crust was absolutely smooth.

On the opposite side of the car the horizon ended in a sunrise glow of a slightly greenish radiance.  From that side the pinkish tint of the surface was quite pronounced.

Before going any lower the doctor, struck with an idea, declared:  “We always want to remember that this car is perfectly soundproof.  Suppose we open the outer door of the vestibule.  I imagine we’ll learn something peculiar.”

It was possible to open this door without touching the inner valves, using mechanism concealed within the walls.  The moment it was done—­the door faced the “north”—­pandemonium itself broke loose.  A most terrific shrieking and howling came from the outside; it was wind, passing at a rate such as would make a hurricane seem a mere zephyr.  The doctor closed the door so that they could think.

“It’s the draft,” he concluded; “the draft from the sun-warmed side to the cold side.”

As for Van Emmon, he was getting out a rope and a heavy leaden weight.  On the rope he formed knots every five feet, about twenty of them; and after getting into one of the insulated, aluminum-armored and oxygen-helmeted suits with which they had explored Mercury, he locked himself on the other side of the inner vestibule door and proceeded to “sound.”

To the amazement of all except Billie “bottom” was reached in less than twenty feet.  “I thought so,” she said with satisfaction; but she was not at ease until Van Emmon had returned in safety from that booming, whistling turmoil.

His first remark upon removing his helmet almost took them off their feet.  “The point is,” said he, throttling his excitement—­“the point is, the rope was nearly jerked out of my hands!

“Understand what I mean?  The surface is revolving!”