David did as he was told, and it sprang from his hands as though it had a primitive life of its own, folding softly and warmly against every fold of structure of his forehead, eyes, and nose; yet it did not prevent him from breathing or from blinking his eyes.
"What has been accomplished?" he asked.
Before the words were out of his mouth there was a mirror before him, manufactured out of energy as silently and quickly as thought itself. In it he could see himself but dimly. His farmboy costume, from hip boots to wide lapels, appeared out of focus through a shadowy mist that changed continuously, as though it were a thin smoke that drifted yet never vanished. From his upper lip to the top of his head all was lost in a shimmer of light that blazed without blinding and through which nothing could be seen. As he stared, the mirror vanished, returning to the store of energy from which it had been momentarily withdrawn.
David asked wonderingly, "Is that how I would appear to others?"
"Yes, if those others had only the sensory equipment you yourself have."
"Yet I can see perfectly. That means that light rays enter the shield. Why may they not leave then and reveal my face?"
"They do leave, as you say, but they are changed In the passage and reveal only what you see in the mirror. To explain that properly, I must use concepts lacking in your mind's understanding."
"And the rest?" David's hands moved slowly over the smoke that encircled him. He felt nothing.
The deep voice again answered the voiceless thought. "You feel nothing. Yet what appears to you as smoke is a barrier which is resistant to short-wave radiation and impassable to material objects of larger than molecular size."
"You mean it is a personal force-shield?"
"That is a crude description, yes."
David said, "Great Galaxy, it's impossible! It has been definitely proven that no force-field small enough to protect a man from radiation and from material inertia can be generated by any machine capable of being carried by a man."
"And so it is to any science of which your fellows are capable of evolving. But the mask you wear is not a power source. It is instead a storage device of energy which, for instance, can be derived from a few moments' exposure to a sun radiating as strongly as ours is from the distance of this planet. It is, further, a mechanism for releasing that energy at mental demand. Since your own mind is incapable of controlling the power, it has been adjusted to the characteristics of your mind and will operate automatically as needed. Remove the mask now."
David lifted his hand to his eyes and, again responsive to his will, the mask fell away and was only a strip of gauze in his hand.
The deep voice spoke for a last time. "And now you must leave us, Space Ranger."
And as gently as can be imagined, consciousness left David Starr.
Nor was there any transition in his return to consciousness. It came back in its entirety. There wasn't even a moment's uncertainty as to his whereabouts; none of the "Where am I?" attitude.
He knew with surety that he was standing on his good two legs upon the surface of Mars; that he was wearing the nosepiece again and breathing through it; that behind him was the exact place at the lip of the fissure where he had thrust the rope ladder's anchor for the beginning of the descent; that to his left, half-hidden among the rocks, was the scooter which Bigman had left behind.
He even knew the exact manner in which he had been returned to the surface. It was not memory; it was information deliberately inserted in his mind, probably as a final device to impress him with the power of the Martians over matter-energy fntercon-versions. They had dissolved a runnel to the surface for him. They had lifted him against gravity at almost rocket speed, turning the solid rock to energy before him and congealing the energy to rock once more behind him, until he was standing on the planet's outer skin once more.
There were even words in his mind that he had never consciously heard. They were in the feminine voice of the caverns, and the words were simply these: "Have no fear, Space Ranger!"
He stepped forward and was aware that the warm, Earth-like surroundings that had been prepared for him in the cavern below no longer existed. He felt the cold the more for the contrast and the wind was stronger than any he had felt yet on Mars. The sun was low in the east as it had been when he first descended the fissure. Was that the previous dawn? He had no way of judging the passage of time during his unconscious intervals, but he felt certain Ms descent had not been more than two dawns before anyway.
There was a difference to the sky. It seemed bluer and the sun was redder. David frowned thoughtfully for a moment, then shrugged. He was becoming accustomed to the Martian landscape, that was all. It was beginning to seem more familiar and, through habit, he was interpreting it in the old Earthly patterns.
Meanwhile it would be better to begin the return to the farm dome immediately. The scooter was by no means so quick as a sand-car nor as comfortable. The less time spent on it the better.
He took approximate sightings among the rock formations and felt like an old hand because of it. The farmboys found their way across what seemed trackless desert by just this method. They would sight along a rock that "looked like a watermelon on a hat," proceed in that direction until level with one that "looked like a spaceship with two off-center jets" and head between it and a farther rock that "looked like a box with its top stove in." It was a crude method but it required no instruments other than a retentive memory and a picturesque imagination, and the farmboys had those in plenty.
David was following the route Bigman had recommended for speediest return with the least chance of going wrong among the less spectacular formations. The scooter jounced along, leaping crazily when it struck ridges and kicking up the dust when it turned, David rode with it, digging his heels firmly into the sockets provided for them and holding a metal steering leash tightly in each hand. He made no effort to cut his speed. Even if the vehicle turned over, there would be little chance for much harm to himself under Martian gravity.
It was another consideration that stopped him: the queer taste in his mouth and the itch along the side of his jawbone and down the line of his backbone. There was a faint grittiness in his mouth, and he looked back with distaste at the plume of dust that jetted out behind him like rocket exhaust. Strange that it should work its way forward and around him to fill his mouth as it did.
Forward and around! Great Galaxy! The thought that came to him at that moment clamped a cold, stifling hand upon his heart and throat.
He slowed the scooter and headed for a rocky ridge where it could stir up no dust. There he stopped it and waited for the air to grow clear. But it didn't. His tongue worked about, tasting the inside of his mouth and shrinking from the increasing roughness that came of fine grit. He looked at the redder sun and bluer sky with new understanding. It was the general dust in the air that was scattering more light, taking the blue from the sun and adding it to the sky in general. His lips were growing dry and the itching was spreading.
There was no longer doubt about it, and with a grim intensity of purpose he flung himself upon his scooter and dashed at top speed across the rocks, gravel, and dust.
Dust!
Dust!
Even on Earth men knew Intimately of, the Martian dust storm, which resembled only in sound the sandstorm of the Earthly deserts. It was the deadliest storm known to the inhabited Solar System. No man, caught as David Starr was now, without a sand-car as protection, miles from the nearest shelter, had ever, in all the history of Mars, survived a dust storm. Men had rolled in death throes within fifty feet of a dome, unable to make the distance while observers within neither dared nor could sally to the rescue without a sand-car.