them--the gleam of spirit that marks those who will not be
downed for long, no matter what the odds. The ray of struggle that only
death could take away.

For a long moment, then, the old man sat buried in thought. At last he
looked up again. Broke the silence.

"Have you ever seen the physical experiment in which a wave of sound is
used to break a glass?"

"No. But I've heard of it. I know what you're talking about."

"Very well, then. Imagine, if you can, that the barrier between space
and time is that glass. It is apparently impenetrable."

"I see." Elaine's fiance nodded eagerly.

"Then try to conceive of a terrific wave of energy being concentrated
against it, just as the sound wave is concentrated on the glass. But
this time, the wave must be so manipulated as to strike the barrier as a
pebble strikes and breaks a window. Otherwise it would be too weak to
break through. Or, if it was strong enough, it would break down the
entire space-time relationship."

* * * * *

Again Mark nodded, this time more slowly.

"You mean that the wave of energy really must be like a sword, stabbing
one small hole through the barrier?"

"Exactly." A pause. "The time mirror represented just such a hole
through the barrier. What appeared to us to be waves in the glass
actually were frozen ripples in the space-time continuum--just as if you
had dropped a stone in water, and the hole and ripples had frozen."

"Then when you looked into the mirror--"

"Your mind went out through that gap in the barrier. Ordinarily, of
course, you would not even know that this was happening. But if your
mind was concentrated on something in the past or future--as Elaine's
was upon the picture of her ancestor--, you were automatically hurtled
through time to that period."

The younger man frowned.

"Then why didn't my mind go, too, when Elaine's did? We both were
looking into the mirror."

"But from different angles," the professor reminded him. "Remember, the
actual break in the continuum was relatively small. Elaine, seated
before the mirror, must have been directly in front of the gap, so she
was sucked through. You, on the other hand--"

"Yes. I was standing up. Off center. So I didn't go." Mark nodded. "I
see."

"And now," said the scientist, "the mirror is broken. Our last chance of
saving Elaine is gone."

"No!"

"What?" The professor peered up at the other incredulously. "What do you
mean, Mark?