ide walls of
the locks, made to receive them.

"Here we go!" cried the captain, the tug began to move slowly
under the pull of the electric locomotives on the concrete wall
above them. "Start your cameras, boys!"

Blake and Joe needed no urging. Already the handles were clicking,
and thousands of pictures, showing a boat actually going through
the locks of the Panama Canal, were being taken on the long strip
of sensitive film.

"Oh, it is wonderful!" exclaimed Mr. Alcando. "Do you think--I
mean, would it be possible for me to--"

"To take some pictures? Of course!" exclaimed Blake, generously.
"Here, grind this crank a while, I'm tired."

The Spaniard had been given some practice in using a moving
picture camera, and he knew about at what speed to turn the
handle. For the moving pictures must be taken at just a certain
speed, and reproduced on the screen at the same rate, or the
vision produced is grotesque. Persons and animals seem to run
instead of walk. But the new pupil, with a little coaching from
Blake, did very well.

"Now the gates will be closed," said the tug captain, "and the
water will come in to raise us to the level of the next higher
lock. We have to go through this process three times at this end
of the Canal, and three times at the other. Watch them let in the
water."

The big gates were not yet fully closed when something happened
that nearly put an end to the trip of the moving picture boys to
Panama.

For suddenly their tug, instead of moving forward toward the front
end of the lock, began going backward, toward the slowly-closing
lock gates.

"What's up?" cried Blake.

"We're going backward!" shouted Joe.

"Yes, the stern locomotives are pulling us back, and the front
ones seem to have let go!" Captain Watson said. "We'll be between
the lock gates in another minute. Hello, up there!" he yelled,
looking toward the top of the lock wall. "What's the matter?"

Slowly the tug approached the closing lock gates. If she once got
between them, moving as they were, she would be crushed like an
eggshell. And it seemed that no power on earth could stop the
movement of those great, steel leaves.

"This is terrible!" cried Mr. Alcando. "I did not count on this in
learning to make moving pictures."

"You'll be in tighter places than this," said Blake, as he thought
in a flash of the dangers he and Joe had run.

"What'll we do?" asked Joe, with a glance at his chum.

"Looks as though we'd h