I _knew_ them. What--I glanced
at Mercer, and he laughed aloud with pleasure and excitement.

"It worked!" he cried. "I received your thought regarding Carson, and
then turned the switch so that you received my thought. And you did!"

Rather gingerly I removed the thing from my head and laid it on the
table.

"It's wizardry, Mercer! If it will work as well on _her_...."

"It will, I know it will!--if we can get her to wear one of these,"
replied Mercer confidently. "I have only three of them; I had planned
some three-cornered experiments with you, Carson, and myself. We'll
leave Carson out of to-night's experiment, however, for we'll need him
to operate this switch. You see, as it is now wired only one person
transmits thoughts at a time. The other two receive. When the switch is
on the first contact, Number One sends, and Numbers Two and Three
receive. When the switch is on Number Two, then he sends thoughts, and
Numbers One and Three receive them. And so on. I'll lengthen these leads
so that we can run them out into the pool, and then we'll be ready.
Somehow we must induce her to wear one of these things, even if we have
to use force. I'm sure the three of us can handle her."

"We should be able to," I smiled. She was such a slim, graceful, almost
delicate little thing; the thought that three strong men might not be
able to control her seemed almost amusing.

"You haven't seen her in action yet," said Mercer grimly, glancing up
from his work of lengthening the cords that led from the antennae to the
control panel. "And what's more, I hope you don't."

* * * * *

I watched him in silence as he spliced and securely taped the last
connection.

"All set," he nodded. "Carson, will you operate the switch for us? I
believe everything is functioning properly." He surveyed the panel of
instruments hastily, assuring himself that every reading was correct.
Then, with all three of the devices he called antennae in his hand,
their leads plugged into the control panel, he led the way to the side
of the pool.

The girl was strolling around the edge of the pool, feeling the smooth
tile sides with her hands as we came into view, but as soon as she saw
us she shot through the water to where we were standing.

It was the first time I had seen her move in this fashion. She seemed to
propel herself with a sudden mighty thrust of her feet against the
bottom; she darted through the water with the