up the steps by which Benny mounted to
the platform on the edge of the tank before he plunged in, Joe poised
there.

"Here I go," he called to Helen. "Got a watch?"

"Yes, Joe."

"Time me then. I'm going to see how long I can stay under water."

In he went head first, making a clean dive, for Joe was an adept in the
water. He swam about in the limpid depths, Helen watching him
admiringly through the glass sides of the tank. Then Joe settled down
on the bottom as Benny was in the habit of doing. Helen nervously
watched the seconds tick off on her wrist watch.

When two minutes had passed, and Joe was still below the water, the
girl became nervous.

"Come on out, Joe!" she called. Joe could not hear her, of course. He
waved his hand to her. He could not stay under much longer, he felt
sure, but he did not want to give up. It was not until three seconds
of the third minute had passed that he found it impossible to hold his
breath longer, and up he shot, filling his lungs with air as he reached
the surface.

At that moment Benny Turton came into the tent, and saw some one in his
tank.

"What happened?" he cried, running forward. "Did some one fall in?"

"It's all right," Helen informed the "human fish."

CHAPTER XI

HELEN'S DISCOVERY

Joe Strong climbed out of the tank. He grinned cheerfully at Benny.

"It was so hot I took a bath in your tub," he explained. "It sure was
fine! Hope you don't mind?"

"Not a bit," returned Benny, cheerfully. "Come in any time you like.
It isn't exactly a summer resort beach, but it's the best we have."

"And Joe stayed under water over three minutes," Helen said.

"Did I, really?" Joe cried.

"You certainly did."

"I was just giving myself a try-out," Joe explained to Benny.

"That's pretty good," declared the "human fish," as he tested the
temperature of the water. "I couldn't do that at first."

"Oh, you see I've lived near the water all my life," Joe explained,
"and it comes sort of natural to me. Don't be afraid that I'm going
after your act though," he added, with a laugh.

"I almost wish you would," and Benny spoke wearily.

"What's the matter?" asked Helen, with ready sympathy.

"Oh, I don't know. I don't feel just right, somehow or other. It's
mostly in my head--back here," and Benny pointed to the region just
behind his ears. "I've got a lot of pain there, and going under water
and staying so long seems to make it worse."

"Why