"Blake, did you hear that?" asked Joe, after a pause, during which he and his chum could hear the low buzz of conversation from the other balcony.

"Yes, I heard it. What of it?"

"Well, nothing that I know of, and yet—"

"Yet you're more suspicious than I was," broke in Blake. "I don't see why."

"I hardly know myself," admitted Joe. "Yet, somehow, that ticking box, and what you saw in that letter—"

"Oh, nonsense!" interrupted Blake. "Don't imagine too much. You think that curious box is some attachment for a moving picture camera; do you?"

"Well, it might be, and—"

"And you're afraid he will get ahead of you in your invention of a focus tube; aren't you?" continued Blake, not giving his companion a chance to finish what he started to say. For Joe had recently happened to hit on a new idea of a focusing tube for a moving picture camera, and had applied for a patent on it. But there was some complication and his papers had not yet been granted. He was in fear lest someone would be granted a similar patent before he received his.

"Oh, I don't know as I'm afraid of that," Joe answered slowly.

"Well, it must be that—or something," insisted Blake. "You hear Alcando and someone else talking about a machine, and you at once jump to the conclusion that it's a camera."

"No, I don't!" exclaimed Joe. He did not continue the conversation along that line, but he was doing some hard thinking.

Later that evening, when Mr. Alcando called at the room of the two chums to bid them goodnight, he made no mention of his visitor on the balcony. Nor did Blake or Joe question him.

"And we start up the Canal in the morning?" asked the Spaniard.

"Yes, and we'll make the first pictures going through the Gatun locks," decided Blake.

"Good! I am anxious to try my hand!" said their "pupil."

With their baggage, valises, trunks, cameras, boxes of undeveloped film, other boxes to hold the exposed reels of sensitive celluloid, and many other things, the moving picture boys and Mr. Alcando went aboard the government tug Nama the next morning. With the exception of some Army engineers making a trip of inspection, they were the only passengers.

"Well, are you all ready, boys?" asked the captain, for he had been instructed by his superiors to show every courtesy and attention to our heroes. In a sense they were working for Uncle Sam.

"All ready," answered Blake.

"Then we'll start," was the reply. "I guess—"

"Oh, one moment, I beg of you!" cried Mr. Alcando. "I see a friend coming with a message to me," and he pointed along the pier, where the tug was tied. Coming on the run was a man who bore every appearance of being a Spaniard.

"You are late," complained Mr. Alcando, as the runner handed him a letter. "You almost delayed my good friend, the captain of this tug."

"I could not help it," was the answer. "I did not receive it myself until a few minutes ago. It came by cable. So you are off?"

"We are off!" answered Mr. Alcando.

Then the other spoke in Spanish, and later on Blake, who undertook the study of that language so as to make himself understood in a few simple phrases knew what it was that the two men said. For the runner asked:

"You will not fail us?"

"I will not fail—if I have to sacrifice myself," was the answer of Mr. Alcando, and then with a wave of his hand the other went back up the pier.

"All right?" again asked Captain Watson.

"All right, my dear sir, I am sorry to have delayed you," answered Mr. Alcando with more than his usual politeness.

"A little delay doesn't matter. I am at your service," the commander said. "Well, now we'll start."

If either Blake or Joe felt any surprise over the hurried visit, at the last minute, of Mr. Alcando's friend, they said nothing to each other about it. Besides, they had other matters to think of just then, since now their real moving picture work was about to begin.

In a short time they were moving away from the pier, up the harbor and toward the wonderful locks and dam that form the amazing features (aside from the Culebra Cut) of the great Canal.

"Better get our cameras ready; hadn't we, Blake?" suggested Joe.

"I think so," agreed his chum. "Now, Mr. Alcando, if you want to pick up any points, you can watch us. A little later we'll let you grind the crank yourself."

I might explain, briefly, that moving pictures are taken not by pressing a switch, or a rubber bulb, such as that which works a camera shutter, but by the continuous action of a crank, or handle, attached to the camera. Pressing a bulb does well enough for taking a single picture, but when a series, on a long celluloid strip, are needed, as in the case for the "movies," an entirely different arrangement becomes absolutely necessary.

The sensitive celluloid film must move continuously, in a somewhat jerky fashion, inside the dark light-tight camera, and behind the lens. As each picture, showing some particular motion, is taken, the film halts for the briefest space of time, and then goes on, to be wound up in the box, and a new portion brought before the lens for exposure.

All this the crank does automatically, opening and closing the shutter, moving the film and all that is necessary.

I wish I had space, not only to tell you more of how moving pictures are made, but much about the Panama Canal. As to the former—the pictures—in other books of this series I have done my best to give you a brief account of that wonderful industry.

Now as to the Canal—it is such a vast undertaking and subject that only in a great volume could I hope to do it justice. And in a story (such as this is intended to be), I am afraid you would think I was trying to give you pretty dry reading if I gave you too many facts and figures.

Of course many of you have read of the Canal in the newspapers—the controversy over the choice of the route, the discussion as to whether a sea level or a lock canal was best, and many other points, especially whether the Gatun Dam would be able to hold back the waters of the Chagres River.

With all that I have nothing to do in this book, but I hope you will pardon just a little reference to the Canal, especially the lock features, since Joe and Blake had a part in at least filming those wonderful structures.

You know there are two kinds of canals, those on the level, which are merely big over-grown ditches, and those which have to go over hills and through low valleys.

There are two ways of getting a canal over a hill. One is to build it and let the water in to the foot of the hill, and then to raise vessels over, the crest of the hill, and down the other side to where the canal again starts, by means of inclined planes, or marine railways.

The other method is by "locks," as they are called. That is, there are built a series of basins with powerful, water-tight gates dividing them. Boys who live along canals well know how locks work.

A boat comes along until it reaches the place where the lock is. It is floated into a basin, or section, of the waterway, and a gate is closed behind it. Then, from that part of the canal which is higher than that part where the boat then is, water is admitted into the basin, until the boat rises to the level of the higher part of the canal. Then the higher gate is opened, and the vessel floats out on the higher level. It goes "up hill," so to speak.

By reversing the process it can also go "down hill." Of course there must be heavy gates to prevent the higher level waters from rushing into those of the lower level.

Some parts of the Panama Canal are eighty-five feet higher than other parts. In other words, a vessel entering the Canal at Colon, on the Atlantic side of the Isthmus, must rise eighty-five feet to get to the level of Gatun Lake, which forms a large part of the Canal. Then, when the Pacific end is approached, the vessel must go down eighty-five feet again, first in one step of thirty and a third feet, and then in two steps, or locks, aggregating fifty-four and two-thirds feet. So you see the series of locks at either end of the great Canal exactly balance one another, the distance at each end being eighty-five feet.

It is just like going up stairs at one end of a long board walk and down again at the other end, only the steps are of water, and not wood.

The tug bearing Blake, Joe and Mr. Alcando was now steaming over toward Toro Point break-water, which I have before alluded to. This was built to make a good harbor at Colon, where violent storms often occur.

"I want to get some pictures of the breakwater," Blake had said, since he and his chum were to present, in reels, a story of a complete trip through the Canal, and the breakwater was really the starting point. It extends out into the Caribbean Sea eleven thousand feet.

"And you are taking pictures now?" asked Mr. Alcando, as Blake and Joe set up a camera in the bow of the boat.

"That's what we're doing. Come here and we'll give you lesson number one," invited Blake, clicking away at the handle. "I will gladly come!" exclaimed the Spaniard, and soon he was deep in the mysteries of the business.

There was not much delay at the breakwater, as the boys were anxious to get to the Canal proper, and into the big locks. A little later their tug was steaming along the great ditch, five hundred feet wide, and over forty feet deep, which leads directly to the locks. This ditch, or start of the Canal proper, is about seven miles long, and at various points of interest along the way a series of moving pictures was taken.

"And so at last we are really on the Panama Canal!" cried Joe as he helped Blake put in a fresh reel of unexposed film, Mr. Alcando looking on and learning "points."

"That's what you are," the captain informed them, "and, just ahead of you are the locks. Now you'll see something worth 'filming,' as you call it."