. See how
green it is?"

A few moments' observation corroborated his statement.

"I'd say," Arthur remarked reflectively, "that it takes about fifteen
seconds for the sun to make the round trip from farthest north to
farthest south." He felt his pulse. "Do you know the normal rate
of the heart-beat? We can judge time that way. A clock will go
all to pieces, of course."

"Why did your watch explode--and the clock?"

"Running forward in time unwinds a clock, doesn't it?" asked
Arthur. "It follows, of course, that when you move it backward in
time it winds up. When you move it too far back, you wind it so
tightly that the spring just breaks to pieces."

He paused a moment, his fingers on his pulse.

"Yes, it takes about fifteen seconds for all the four seasons to
pass. That means we're going backward in time about four years a
minute. If we go on at this rate another hour we'll be back in the
time of the Northmen, and will be able to tell if they did discover
America, after all."

"Funny we don't hear any noises," Estelle observed. She had caught
some of Arthur's calmness.

"It passes so quickly that though our ears hear it, we don't separate
the sounds. If you'll notice, you do hear a sort of humming.
It's very high-pitched, though."

Estelle listened, but could hear nothing.

"No matter," said Arthur. "It's probably a little higher than your
ears will catch. Lots of people can't hear a bat squeak."

"I never could," said Estelle. "Out in the country, where I come
from, other people could hear them, but I couldn't."

They stood a while in silence, watching.

"When are we going to stop?" asked Estelle uneasily. "It seems as
if we're going to keep on indefinitely."

"I guess we'll stop all right," Arthur reassured her. "It's obvious
that whatever it was, only affected our own building, or we'd see
some other one with us. It looks like a fault or a flaw in the rock
the building rests on. And that can only give so far."

Estelle was silent for a moment.

"Oh, I can't be sane!" she burst out semihysterically. "This can't
be happening!"

"You aren't crazy," said Arthur sharply. "You're sane as I am. Just
something queer is happening. Buck up. Say your multiplication
tables. Say anything you know. Say something sensible and you'll
know you're all right. But don't get frightened now. There'll be
plenty to get frightened about later."

The grimness in his tone alarmed Estelle.

"What are you afraid of?"