across the ground in a crawling distortion—was quite visible. Its amplitude died as it spread until it was invisible.

Minutes later, a contracting circle of shock-wave appeared. It converged and closed down on the spot that was still covered by the tiny cloud. There was considerable amplitude at that spot where all the energy returned, then the concentric shock wave raced away from the point again.

"I'd like to see the antipodes," muttered Ackerman.

"We'll see others," Blaine promised.

"That was the same shock wave, wasn't it?" Laurie wanted to know.

"Yes," said her father, watching through his telescope. "It started from that city and spread out across the earth. On the other side, of course, the thing converged to zero, passed through itself and spread out again. It returned to its origin—and will continue to encircle the earth until it dies. Each time it is less perfect because of wave-diffraction and refraction due to a non-homogenous medium. That tends to spread it out, makes its focal point imperfect. Its energy will be dissipated in heat due to resistance. It will eventually die and—"

"Here comes one!" exploded Laurie. "From the other side."

They watched. The shock wave converged, growing in amplitude as it circled down to the pinpoint. There was a clouding at the focal point where earth itself ground itself to bits in the grip of a transmitted wave of energy. The receding wave spread out again.

Fascinated, horror-stricken, Ackerman, Laurie Blaine, and her father watched the Earth being consumed by atomic fire.

Then, as though the enemy had been searching out their target—bracketing it—other pinpricks burst in widely separated places. The criss-crossing of concentric shock waves cast up high peaks that raced along, tearing up the very ground.

"On earth," said Blaine, "Nine hours have passed since the initial blast."

More time passed, and then with the target accurately bracketed, the pinpricks of energy burst again and again and again in lightning speed. The face of Terra sparkled; scintillated. The ground writhed and boiled; mighty gouts of earth and tortured stone burst upward where the bursts of power drove below the surface. The scintillating face of the earth increased to a constant glow as the ferocity of the attack 

 Prev. P 22/61 next