Some of the old man's elation dropped away. He shook his head.
"Not yet. We know only the effect we want. But how to achieve it—" He shrugged.
Experiments. More experiments. Hours of experiments, with Mark and the professor hovering over an electric crucible bubbling with molten glass.
Hours of failure.
At last the old scientist straightened, his face haggard with weariness.
"It is no use," he said sadly. "I have exhausted my knowledge, and to no avail."
He turned away, shoulders sagging. Stumbled toward the door.
The next instant Mark's voice rose in a scream.
"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.