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."