"What?" The professor peered up at the other incredulously. "What do you mean, Mark?"
Brown eyes narrowed with excitement, Elaine's sweetheart held out the splinter of glass he had picked up. He shook it in front of the savant's face.
"Professor, every piece of glass that went to make up that mirror is laying over there on the floor."
"I am sorry, my boy." The elder man frowned. "I do not understand."
"Professor, if you break your glasses, all you have to do to get a new pair is to take the pieces to an optician. He'll figure the formula of the lens from the fragments and make you a new set."
"You mean—"
"I mean that we can put the pieces of that mirror together as if it was a jigsaw puzzle. From it, you can figure out some kind of a formula. Then, by experimenting, you can find what kind of energy bolt it takes to blast through the barrier!"
Something of the man's intensity, his enthusiasm, communicated itself to the professor. His blue eyes came alight.
"It is conceivable!" he declared. "Not likely. But conceivable." He gripped the fragment of glass which Mark held. "Yes! We shall try it! If it works, we can—"