But after a time he wondered idly what had happened to the ghost. Perhaps it had taken pity on him and wasn't going to haunt him in his present predicament, anyway. Whatever the reason, the absence of that high-pitched screaming was one small blessing to be thankful for.
Or was it? Even as he thought about it he shifted his one free leg and the sound piped faintly in his ears. The irritating, knifelike vibration channeled through every nerve path and shook his body. He kicked out violently in an effort to shift position and ease the aching spots of contact between his body and the suit.
The sound surged to a higher, more racking pitch, then passed beyond audibility.
Ghosts.
In a spacesuit. In an icebox. He laughed sharply without humor. Our suits may spread eagle, but they don't scream. Johnson would be pleased to have his confirmation that they did scream. As if Johnson would ever know what he found out -
He clenched his teeth. If he was going to die here, he could at least die sane. And if his brain were still functioning he should be able to figure out that scream.
What makes sound? Vibration. Of what? He thought of all the elements of the suit that might vibrate. There weren't any. Unless —
Air columns vibrate. But there weren't any air columns. No — but there was air going through an orifice. That made a whistle. Suddenly he laughed out loud. He kicked his leg sharply and listened to the resulting shrill scream.
"Hello, ghost," he said.
It was the pressure regulator valve in the back of the suit. Every time a joint of the suit moved the volume decreased or increased with a change of air pressure inside that might be as much as a hundred percent. The regulator valve took care of that. As the volume decreased the valve drew off some of the air to a low pressure tank. As the volume increased, it passed back some of the air from a high pressure tank, thus maintaining constant air pressure within the suit regardless of the contortions of the occupant. When the low pressure tank was filled, an automatic pump evacuated it to the high pressure tank.