"Death traps!" muttered Val. "What is the reason for all this murdering?"
It was Townshend who answered. "Doesn't it begin to become evident that all this is a brilliant posthumous scientific trap built by a dying race for a definite reason? Maybe there's not so much mystery about it at all. All the other planets, as we well know now, are barren. If any living beings came here they'd have to be Earth people—and the chance of beings coming from systems way out among the stars is totally unlikely. Yes, it had to be Earth people—and when they had become clever enough to get here it meant they had an advanced civilization."
"What are you driving at?" demanded Cliff.
"Just this. No race as advanced as the Martians must have been to build this complex machinery would be petty enough or impractical enough to plan a mere death trap to operate after their demise. They had a specific and vastly important reason. Maybe this is all a test. A trap like this would eliminate an intruder not sufficiently advanced to measure up to the mysterious Martian purpose. Somehow that purpose is connected with that giant ticking ball down below."
"Sense in that," Cliff admitted, and added wryly. "If you're right, it looks as if we don't measure up to Martian standards. So far we've qualified only for the elimination class."
"Right," agreed Val. "We've got to solve the purpose behind that tick-tocking ball."
"In the meantime, Sparks, radio to Earth. Tell them to send blast furnaces and to try and unlock the surface valves. We'll bury Gilby and get to work below with the x-ray machines and flame gun batteries. We've little manpower now, and we've got to act fast. Let's get started—"
He halted abruptly as he saw Sparks was trying to interrupt him.
"What's the matter?"
"That's the news I was trying to tell you I have," Sparks said. "We can't radio. The batteries are dead. Some sort of radiation has burned them all out!"
CHAPTER IV
The Pendulum
ONCE Gilby was buried and a short service recited over his grave, the five returned to the depths, lowering their equipment down the shaft so that it missed the photoelectric eye. They reached below in safety. Sparks leaving his useless radio to help.
"You get to work on the smaller balls with the batteries and furnaces; I'll x-ray the big one," Townshend said, and immediately set about the erection of his equipment.
The next two hours were filled with intense activity for all of them, but as far as the flame gun batteries went they had no effect. The balls refused to melt. Even the limited furnaces at their disposal only warmed them.
On the other hand Townshend met with success and pointed to the cine x-ray screen triumphantly. The rays, passing through the globe, gave a hazy shadowgraph moving picture of what was going on inside. In amazement the others stared on the multitude of black-outlined machinery, intersected cog upon cog, linking up with whole masses of complex mechanism and dominated by a mighty pendulum swinging deliberately to and fro.
"What the devil is it?" demanded Cliff blankly.
Townshend regarded it thoughtfully.
"So far as I can tell it is a cosmic clock—about one of the cleverest ideas
