These seemingly invincible creatures could not have come from this world. Biological development comes through struggle and survival. An invincible creature does not have to worry about its existence--in fact, struggle was necessary to develop an invincible being. These spheres must be from another world.

Refugees, perhaps, from another, even more powerful race; or maybe they were seeking a new world to conquer.

One was circling overhead again. The leaves rustled. Taylor thought he heard a choked-off scream. Orkins. He gritted his teeth grimly.

There was only one link of hope in Taylor's chain of thought.

There must always be a check to every form of life. Terrestrial plagues of insects were followed suddenly by flocks of birds. In western states an increase in the number of jackrabbits always is a forerunner of an increase in the number of coyotes. But the jackrabbits carried parasites fatal to the coyotes. If man was a rabbit, then perhaps he harbored the check to these creatures of flame.

What check would limit the whispering spheres? No germ, surely.

What possible check was there except man's nature? What part of man's nature? That was the answer Taylor wanted to know.

His chain of thought was suddenly interrupted.

Pember was coming on the run. The private saluted the captain.

"Something's wrong, sir! Orkins is throwing a fit."

"Can't you quiet him? The spheres are near."

"Norden held his hand over Orkins' mouth, but it made Orkins worse. I--I think it's serious, sir."

Taylor followed Pember to the place where Orkins had been digging. Norden was there, bending over Orkins, who lay on the ground. Masters, standing behind Norden, shook his head.

"He's dead," Norden said, straightening.

"He was scared to death by the spheres," Masters said. "No one harmed him, except to hold a hand over his mouth. He wasn't choked. He could have breathed through his nostrils--"

"Wait--"

Taylor held up his hand. Something clicked in his brain.

Masters had said something about the spheres that fitted. He said, _Maybe you don't have to touch 'em to kill 'em._ Figuratively speaking, Orkins hadn't been seriously touched either.

The answer!

CHAPTER V

AN ESCAPE

Taylor ordered Pember and Norden to bury Orkins where he had been digging, then the officer took Masters aside.

"We've got a weapon," Taylor announced.

Masters grunted:

"Yeah? Indians had bows and arrows, too. Look at what happened to them."

"This is different. A new weapon. We can beat the spheres through their emotions."

"You mean fear, love, hate--all that stuff? How do you know these spheres have emotions?"

"What is life but a series of sensations and emotions? If the spheres are alive, they must have something which correspond to emotions. The emotions may be different from ours, but they'll be emotions just the same. Orkins died of fear. Of course, you can call it heart attack, but fear brought it on. That sphere that had me cornered in the plant died, too. Do you see?"

"Was the sphere afraid of you or the tunnel?"

"Don't be flippant. The emotion wasn't fear. It might not have been any emotion we have, but an emotion that we'd expect a creature made of energy to have. An emotion of frustration! It had me cornered. I escaped. The energy sphere met resistance.

When energy meets resistance it changes!"

"I don't get it."

"Look, Masters. If the spheres are mixtures of energies, like we are mixtures of chemicals, death means extinction, just as biological death means the extinction of the chemical action in our lives. Theologians say we don't die--that there's a change and we go on existing in a spiritual life. Now let's take a peep at what science tells us about energy: Newton says energy is never extinguished. When it ceases in one form, it changes to another. What happens when you run electricity through a resistance coil?"

"It turns to heat, of course!"

"And when you enclose light where it can't escape?"

"It turns to heat!" Masters' face brightened. "And if you pen up heat, it turns to light. I learned that in school. Resistance causes a change. But what do the spheres turn to?"

"Radio energy, Masters! Something absolutely harmless to man.

These living, energy spheres will change to radio energy when they meet resistance. Frustration is resistance. Frustration is an emotion. An overwhelming emotion for the spheres! The sphere is frustrated--meets resistance--it disappears. In other words, it dies!"

From the city came screams and cries. The spheres had attacked at last.

The men in the wooded field could see the darting b.a.l.l.s sending their searing bolts down on the heads of hapless victims. The cras.h.i.+ng roar of the slaughter sounded like distant thunderstorms.

Streets were jammed with panic-stricken human beings, fleeing from the unknown menace which slashed with bolts of heat energy.

From the hole in the factory roof poured more spheres to join the destruction.

"They breed fast, the devils!" said Masters.

A figure in khaki approached Taylor. It was Pember with blood running from a cut on the side of his head. He saluted briskly.

"Norden escaped, sir!" he blurted. "The dirty so-and-so cracked me over the head with the trench tool and got away!"

"I never thought he'd turn yellow," Masters said. "Well, maybe it's a good thing he's gone. I never trusted him anyhow."

"Which way did he go?" Taylor asked.

"He went toward the factory, sir!" Pember replied. "He didn't knock me out. Just a glancing blow. I was too dazed to stop him, but I saw him running toward the factory."

"He'd rather take it that way than the firing squad, I guess,"

Masters decided.