"_Look out!_"

Instinctively, without so much as a backward glance, the old man lunged
forward. Even as he did so, he felt something jerk at his ankle. His leg
came out from under him. He pitched to the floor.

_Crash!_

The crucible was falling, jerked from its place atop the lab bench! The
electric cable which supplied its current was twisted about the
professor's ankle, somehow unconsciously caught by his foot as he
worked.

Molten glass burst out of the pot in a white-hot wave. Slopped over the
composition floor in a steaming river. Engulfed table legs and radiator
pipes alike.

And then, like a writhing snake, the high tension line from which the
crucible cable stemmed was whipping down, torn loose by the jar of the
professor's leap!

Down it came! Struck the floor once. Lashed against the glass-engulfed
radiator pipes, bare wires flashing.

A ball of purple fire exploded at the contact point, while the cable
jerked and twisted like a living thing. The laboratory was suddenly
permeated with ozone's peculiar odor.

"Look out!" cried Mark again.

* * * * *

But already Professor Duchard had jerked his foot free of the crucible
line. He shrank back under the long bench, away from the writhing cable.

An instant later the current went dead. The crackling ball of purple
fire evaporated into thin air.

Mark sprang across the room to where the scientist lay. He pulled him to
his feet.

"Are you all right, professor? Are you hurt?"

"Yes, yes, my boy. It was a narrow escape, but your warning saved me. I
am all right."

The savant leaned against the bench, trying to still the reflexive
trembling of his body. His face was pale. He ran his tongue over lips
suddenly gone dry as he stared down at the broken high tension line, and
thought of what would have happened had it touched him in its spasm.

And then, suddenly, his blue eyes went wide with stark amazement.

"Mark!" he gasped.

"What's wrong, professor? What is it?"

"That glass on the floor! Look at it!"

The other stared uncomprehendingly.

"The waves, Mark! See the waves!"

A startled exclamation burst from the younger man's lips. He dropped to
his knees. Scrutinized the puddle of glass.

But the scientist pulled him erect again.

"My instruments!" he ordered in a voice that trembled. "Quick! I must
make tests--"

For half an hour he worked. And when at last he straightened, complete
confidence gleamed de