eady been cut away, the action of the water on the
other side would undermine the sand there and gradually straighten up
the cylinder. At least, that was the idea."

"And did it work?"

"Perfectly. Two days passed before the cylinder was absolutely level,
and in the meantime the tug had taken one of the barges for more stone.
Another hundred tons was dumped down as soon as the cylinder was
straight again, and it was thereby kept from further scouring. The
weather had become good again, and the concrete work was continued. On
April 21st the entire gang began work. Barge hands, cooks, everybody
that could handle a shovel at all, was sent aboard the cylinder."

"Did you go?"

"You bet I did, and I worked as hard as any of the men--for a while. Two
or three hours of it did me up, though. I was only twelve years old,
remember, but most of the men kept on the job for forty-eight hours
straight with only fifteen minutes allowed for meals. By that time the
foundation was secure with thirty feet of solid concrete twenty-two feet
thick."

"That ought to hold it," said Eric.

"That was only the beginning," said his friend. "What would hold it,
resting on the top of the sand?"

"I'd thought of that," admitted the boy, "but I supposed the weight
would be enough to drive it in."

"Never," the other said. "The next step was to drive it down into the
hard sand at the bottom of the bay. Father had made borings and found a
true sea-bottom sand fifteen feet and a half below the level of the
shoal. It was to that depth that the whole caisson had to be sunk.

"You remember that I told you there was an air-shaft in the middle of
the caisson?"

"Yes."

"Well, on the top of this air-shaft an air-lock was built. The water in
the air-shaft was forced out by compressed air and the men entered the
caisson."

"Into the compressed air?"

"Yes. It takes a special kind of worker for the job. In the air-lock,
you know, the men have to stay for a while before they enter the
chamber, so as to get used to the compressed air gradually. Lots of
people can't stand it."

"Did you try it?"

"Yes. I asked Father and he wouldn't let me. But I slipped into the
air-lock once and tried it, anyhow."

"Well?"

"Not for me!" said his friend. "I got out in less than five minutes. My
head seemed bursting, and I was bleeding from the ears as well as the
nose. But some of them, especially an old chap called Griffin, the
foreman, didn't seem to min