"

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--"

He stopped short. His face fell.

"We can what?" he finished. "Another time mirror will not help us bring
Elaine back--"

His companion interrupted fiercely:

"How do we know? There's always a chance we'll think of something, isn't
there? And it's a cinch we won't accomplish anything just sitting here."

"But--"

"The least we can do is try!"

They worked like madmen in the hours that followed, heedless of the
wedding guests who came and went from the house in bewildered knots.
Unmindful of gashed fingers, Mark fitted the slivers of mirror together,
while Professor Duchard tested and analyzed and figured at his side.

And then--

"I have it!" shouted the savant triumphantly. "I have the formula!"

"Then we can construct another mirror?"

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.