ng.

Phil bent his head in the dumbness of profound despair.

PART V

_The Reversible Equation_

Despair, however, is a luxury. Necessity is a stimulus. With the
parchings of thirst and the gnawings of hunger, the two young people
ceased swearing and weeping. Phil got up and paced about and sat down
again. Ione's tears stopped and dried, and she sat and thought.

In the back of her mind there had been forming a vague sort of an
idea, which had signalled ahead of itself that there was hope. She sat
there and desperately drove her reason to its utmost efforts, to find
that idea and bring it to the surface of consciousness. Hand to hand
fights with wild animals, battles between ships of the line, vicious
duels between ace-aviators in the clouds are tense fights; but they
cannot compare in anxious difficulty with the struggle to bring up an
unformed idea out of the subconscious mind--especially when one knows
that the idea is there, and that it must be found to save one's life.

"Ione!" exclaimed Phil. It was the first time he had used the name.
"What is the matter? You are as tense as a--"

"Ah!" cried Ione, springing up. "Tense! Tensors! I have it!"

Phil gazed at her in alarm. She laughed; at first it was a strained
laugh, but gradually it melted into her sunny one.

"No, I'm not crazy. I knew there was a way out, and I've been trying
to reason it out. How simple. You remember the little jolts when you
pulled at the vines and when you kicked the funny animal? Tensors.
Matter and space are so closely interrelated that you can't move
matter in or out of space without causing disturbance, recoils, and
tremors in space. Those bits of matter were small, and produced only a
slight disturbance. It takes about a hundred pounds of lead to swing
this segment--"

"Oho! Got you!" exclaimed Phil. "Not so dumb! The safe!"

"Yes. The safe!" Ione cried.

"Throw it off and watch us swing, eh? What would happen?"

"I might calculate it if I knew the weight of the safe."

"No calculating when I'm around," Phil said. "It couldn't make things
any worse. Try it first and calculate afterwards."

* * * * *

They got behind the safe and pushed, and their combined strength
against it was about as effective as it would have been in moving the
Peoples' Gas Building. They sat down again in despair.

"Suppose we _could_ budge it," Ione said. "All we could do would be to
push it around, this piece