One of them walks with a slight favour to his left leg. They were headed down the valley." He touched one of the footprints in a sandy patch. An antlion had built its tiny cone-shaped trap in the toe of the spoor, giving the tracker an accurate timing.
"Six to eight hours," said the tracker, "during the night.
They went on the path, but we cannot follow them, their spoor has been covered by others."
"If we cannot find where they are going, then we will see where they came from," said the sergeant. "Backtrack them! Three hours later, th8 4sergeant walked up to the wreck of the Cessna.
raig slept for a few hours and then by the light of the paraffin lantern began modifying the oxygen equipment for use underwater. The central part of his primitive oxygen rebreathing set was the bag. For this he used one of the inflatable life-jackets. Oxygen from the steel bottle was introduced into the bag through the oneway valve of the mouthpiece, the connection made with a length of flexible tubing.
As he worked, Craig explained, "At a depth of forty feet underwater, the pressure will be greater than two atmospheres you remember your high school physics: thirty-three feet of water equals one atmosphere, plus the pressure of the air above it two atmospheres, right?" His interested audience of three made affirmative sounds.
"Right! So for me to be able to breathe freely, the oxygen has to be fed into my lungs at the same pressure as the surrounding water the oxygen in the bag is under the same ambient pressure as I am, et voild!"
"My old daddy always used to say, it's brains what counts!" Sally-Anne applauded him.
"The chemicals in these two canisters remove the water vapour and carbon dioxide from the air that I exhale, and the purified oxygen goes back into the bag via this tube, and I breathe it again." He was sealing the new connections to the bag with epoxy cement from the repair kit.
"As I use up the oxygen in the bag, I keep topping it up with fresh oxygen from the steel bottle strapped on my back. Like this-" he cracked the tap of the black-and white-coded bottle and there was an adder hiss of escaping gas.
"There are a few problems, of course-" Craig began work on altering the shape of the face-mask to give him a watertight fit.
"Such as? "Sally-Anne asked.
"Buoyancy," Craig answered. "As I use up the oxygen in the bag I will become less buoyant, and the steel bottle will pull me down likea stone. When I top up the bag I'll tend to shoot up likea balloon." "How will you beat that?" J will weight myself with rocks to get down to the tomb entrance, and once I'm there, I'll rope myself down to stay there." Craig was making up a backpack on which were suspended the two canisters and the oxygen bottle. Carefully he positioned the steel bottles so that he could reach the tap over his shoulder.
"However, buoyancy isn't the big problem," he said.
"You've got more?" Sally-Anne demanded.
"As many as you ask for," Craig grinned. "But did you know that pure oxygen breathed for an extended period at more than two atmospheres absolute, that is at any depth below thirty-three feet, becomes a deadly gas, as lethal as the carbon monoxide in the exhaust fumes of an automobile?"
"What can you do about that?"
"Not much," Craig admitted. "Except limit the duration of each dive, and monitor my own reactions very carefully while I am working at the wall of the tomb."
"Can't you work out how much safe time you will have before it starts to poison-" Craig interrupted. "No, the formula would be too complicated and there are too many variables to calculate, from my body mass to the exact water depth. Then there is a cumulative effect %f the poisoning. Each successive dive will become mar risky."
"Oh my God, darling." Sally-Anne stared at him.
"We will keep the dives short, and we will work out a series of signals," Craig reassured her. "You will give me a rope signal from the surface every minute, and if I don't reply or if my reply is not immediate and decisive, you will haul me out. The poisoning is insidious but gradual, it will affect my reactions to the signal before I go out completely.
It gives us a little leeway." He set the bulky equipment carefully aside, close to the fire, so that the warmth would hasten the setting of the epoxy cement.
"As soon as the joints are sealed, we can test it, and then go for the bank."
"How long?"
"It's twenty-four-hour epoxy."
"So long?"
"Rest will increase my resistance to the effects of oxygen poisoning." he forest was too dense to allow the helicopter to alight. It hovered above the tree-tops, and the flight engineer on the winch lowered Genenil Peter Fungabera into a hole in the mat of dark green vegetation below them.
Peter turned slowly on the thin steel cable, and th down-draught from the rotors fluttered his camouflage battle, smock about his torso. Six feet above the earth, he slipped out of the padded sling and dropped clear, landing neatly as a cat. He returned the salute of the Shana sergeant who was waiting for him, cleared the drop area quickly and looked up as the next man was lowered from the hovering helicopter.
Colonel Bukharin was also dressed in camouflage and jump helmet. His scarred face seemed impervious to the tropical sun, it was bloodless and almost as pale as those cold arctic eyes. He shrugged off the helping hands of the Shana sergeant and strode on up the valley. Peter Fungabera fell in beside him and neither man spoke until they reached the crumpled and shattered fuselage of the Cessna.
"There is no doubt?" Bukharin asked.
"The registration, ZS-KYA. You must remember I have flown in this aircraft," Peter Fungabera replied, as he went down on one knee to examine the belly of the fuselage. "If further proof is needed," he touched the neat puncture in the metal skin, "machine-gun fire from directly below."