The captain no longer interfered in any way with the actions of his young guests. They were entirely free to do as they pleased on the ship, and apparently were under no surveillance. As they came on deck on the fourth morning at sea, the day was beautifully bright and clear. The sky was taking on that peculiar blue that is seen only in the lower latitudes. The atmosphere seemed to have thinned, and the horizon to have moved away a mile or two. The sea was as smooth as glass and the steamer was ploughing her way along at the rate of fifteen knots (miles) an hour. As usual, the decks were deserted, with the exception of the man at the wheel and the two lookouts who were always on post, day and night, no matter how clear the day, or how unnecessary the double watch might seem.

It was the custom of the boys in the morning to distribute themselves around the deck so that they could take in all the points of the compass, and for a time each would study the horizon with careful scrutiny, in the hope of sighting some vessel to which they might signal. Everything had been carefully arranged so that as soon as a ship of any sort was seen, word was to be passed quietly from one to another without attracting the attention of anyone on deck, and then each knew his duty.

Hamilton was the custodian of the flags. On him rested the responsibility of displaying the signal so that the passing ship might read the message.

The boys had studied the compass and the maps that were each day displayed in the captain's cabin, and they knew that they were headed south. Although that gave them little or no clew to their ultimate destination, they felt some comfort in the knowledge that the shore of America lay to the starboard, and away off somewhere beyond the dreary horizon was the country they all loved, and where their anxious friends and families were awaiting some word from them.

Bert's post was a little forward of the beam on the starboard side. As he took his place this morning, his heart was heavy. He was thoroughly tired of the monotony of the voyage, and the mystery that enveloped the ship was beginning to wear upon him. For days now they had sailed without seeing anything but a dreary expanse of water on every side, unbroken by anything that was human. Porpoises played around the bows of the steamer, and gulls shrieked as they swooped above her. Now and then a fish leaped out of the water as the steamer ploughed through the waves.

Bert leaned on the rail with his chin resting in his hands and his eyes fixed upon the blank before him. Suddenly he raised his head, and an expression of surprise crept into his face. He turned and looked stealthily around him. Harry was slowly walking up and down the main deck just aft of the fo'c'sle where the lookouts were stolidly pacing.

Bert again turned his eyes toward the horizon. What appeared like a thread in comparison with the vastness of space around them wavered above a small black speck. Bert watched it with eager eyes. At this moment Harry stopped in his walk as he approached the starboard side, and placing his arms on the rail looked out over the sea in the direction of the black thread. Then the boys turned to one another and a questioning glance passed between them. Little by little they moved in toward one another until they met.

Harry looked carefully around him before he whispered:

"Bert, I think it is a steamer."

"I'm sure of it, Hal. Have you got the signals ready?"

"I can get them in a minute, but she is too far away yet."

"You know passing vessels always study one another with a glass."

"But I do not believe she could make out our signals even with a glass, yet."

At this moment one of the men on lookout turned and looked up at the second mate, who silently paced the bridge.

"Steamer off the starboard bow, sir," he said, quietly.

"Keep closer watch. I've seen her," replied the mate, gruffly.

"Aye, aye, sir," came the usual response, without a change in tone.

Involuntarily the boys turned their eyes aft to the captain's cabin. As they did so the door opened gently and the natty, flannel-garbed figure of the commander moved out onto the deck and to the bridge. He carried a glass in his hand, which he raised to his eyes after he had spoken a few words to the mate.

"I thought so," said Bert, dolefully. "You can't lose him."

"Never mind," said Harry, "if she comes near enough I will get the signals up before he can stop me, and we will have to take chances on their being read before he can get them down."

"But aren't you afraid of what he may do?" asked Bert, in some fear.

"What can he do?"

"He seems to be capable of doing a whole lot that might be unpleasant. For instance, he might put you in irons and chuck you down in the hold."

"I do not think he would dare do that. But anyway, I am going to take the chance. We owe it to the folks at home."

"You are right there, Hal. I'm with you whatever comes of it."

"Oh, he's not a cannibal, or a pirate. He might be pretty mad and perhaps use us a bit rough at first, but I think he would laugh at it afterward, when he recovered his temper."

"Gee, but think of all the unpleasant things that might happen before he decided that it was time to laugh."

Harry smiled at the mournful face of his chum, and turned again to look at the speck in the distance. Seemingly, it had grown larger. The captain, who had finished his scrutiny, looked down at them and smiled and waved his hand.

"Sleep well, lads?" he called to them pleasantly.

They nodded sheepishly in reply.

"I can't help liking him," replied Bert.

"There is something big and honest about him like a Newfoundland dog," answered Harry. "I feel sort of mean about trying to trick him. He would be a good friend and a mighty bad enemy."

The captain took another look at the approaching vessel, spoke in a confidential tone to the mate, and again disappeared into his cabin.

"She's coming on," said Harry, with satisfaction. "Unless she changes her course, I will send up the signals in five minutes." He looked at his watch as he spoke. "Pshaw, I'm always forgetting that the salt water has somewhat interfered with the internal arrangements of this affair," he continued, laughing.

By this time the strange steamer was pretty well hull up and the boys could distinguish her masts and funnel as well as see what appeared to be flags fluttering in the breeze.

"In order that we shall not cause any suspicion, Bert," said Harry, presently, "you go and get the Midget and stroll forward. I do not need your help any more than to distract attention from me as much as possible."

Bert turned, and walking around the deck, joined Mason who, while he had heard the call of the lookout man and knew that there was a steamer in sight, had not deserted his post, although he was keen with anxiety when Bert reached him.

"Where is she?" he asked, eagerly.

"She's off the starboard bow, but don't ask fool questions. Move up forward so that Hal can get a chance to have the flags up."

Although burning with a desire to watch the proceedings, the boys kept their faces steadfastly turned to the bow as Harry began in an unconcerned manner to work his way aft. He slowly climbed the companionway that led to the upper deck, and carelessly approached the mast to which the signal halliards were attached.

He stood there for a moment as if watching the oncoming steamer, but his eyes were scanning the decks and the bridge on which the second mate slowly paced to and fro. Then he turned his back to the mast and as he stood with his hands clasped behind him, he cast off the halliards from the cleat to which they were fastened. He was almost concealed from view by the big mast.

When he had loosened the ropes, he turned quickly, and taking the end of another rope from under his coat tied the two together. After one final peep around the mast he threw his coat open boldly, made several quick turns and unwound from his body the rope to which the signal flags were attached. Then with a strong pull he began to send them aloft rapidly.

As the colors sped upward and broke into the wind, his heart almost stopped beating from excitement.

Now they were half way up to the masthead and no one had seen them. The second mate still paced the bridge with his back to him. He glanced at the captain's cabin. No one appeared from there.

"I shall get them up," he whispered to himself through his tightly shut teeth, "but will they be read?"

Now they were chock with the pulley block and he made the ends of the halliards fast to the cleat and stood back to view his work. It seemed scarcely possible that they should not be seen and read by the passing steamer which was now so close that he could almost make out her colors with the naked eye.

With a feeling of triumph he looked aloft at the flags that, aided by a friendly breeze and the motion of the steamer, were fluttering out straight from the masthead. As he dropped his eyes from aloft he started back with a slight cry of fear and surprise.

The head of Suarez, the mate, appeared above an after companionway, his eyes flashing with anger. He rushed at the boy like an enraged animal, but Harry, determined to protect his signal as long as possible, stepped to the mast and took a capstan bar from its place at the base and stood defiantly awaiting the onslaught of the mate, who rushed upon him regardless of his threatening attitude. Before Harry knew what had happened the bar flew out of his hands, and he lay sprawling on the deck from a blow from the open hand of the mate.

Suarez paid no further attention to him, but seizing the halliards hauled down the signal. The scuffling of feet and the fall of the heavy capstan bar caused the second mate to turn quickly, and at the same moment the captain's door opened and he stepped out on the deck. His face flushed with anger as he saw the signal-flags, and then he turned quickly to the other vessel.

As he did so, Harry, whose eyes followed his, saw what he believed to be an answering signal, creep up the mast of the passing steamer. Suarez saw it, too, for he turned to Harry with an ugly look in his eyes.

"The mischief is done, you young devil," he said.

"I hope so," answered Harry, quietly rubbing the arm on which he had fallen. "Your hand is heavy, Suarez."

"I am sorry if I hurt you, Master Hamilton," said the man, somewhat more calmly, "but you are guilty of insubordination and you have broken your word to the captain."

"You are mistaken, Suarez," said a deep voice behind them, and they both looked quickly around to find Captain Dynamite beside them, his glass raised to his eyes as he scanned the passing steamer. "Master Hamilton made me no promise; in fact, he warned me that he would take the first opportunity that presented itself to get ashore, or to communicate with a passing ship. He has been too sharp for us, that is all."

"Message received all right, captain?" asked Harry, eagerly.

Dynamite smiled at the boy's assurance.

"Yes, received and acknowledged," he answered; and then turning to Suarez he continued, in a low tone:

"I do not think it has done any harm. She does not apparently wish to learn anything further of us."

"Captain Dynamite," said Harry, warmly, "there is a big load off my mind, and now we will stick to you through thick and thin. We owe our lives to you, and we are not ungrateful. Whether you wish to take us into your confidence or not, I do not believe, whatever may be the mystery of your voyage, that there is anything dishonorable about it, and you can count on us as part and parcel of your crew. We have succeeded in getting word to our friends at home as I told you I would try to do; now we are yours to command."

The captain looked down into Harry's earnest face, his own quite serious and solemn.

"You are a fine lot of lads," he said, "and if I was on a pleasure cruise I would not ask for better companions, but look you, this voyage of mystery, as you call it, is a very serious piece of business and I wish you were all safe ashore and well out of it."

"But we don't want to be out of it, captain," asserted Harry, stubbornly. Bert and Mason had now joined the group on the after deck.

"No, captain," piped the Midget, "we are in it so far and we want to stick. You can't chuck us overboard very well, and as long as we have got to be a part of your expedition, I think you better muster us in as a part of the crew."

"Well, youngsters, as much as I regret it, you may have to cast your fortunes in with ours after all, but until that necessity arises we will go along as we are, I your host and you my unwilling guests."

"No, not unwilling now, cap," replied Mason. "So long as the folks know we are safe and sound I think I had rather be aboard this queer craft with you than any place I can think of just now. What do you say, Bert?"

"Right, as usual."

"Well, boys, while I have perfect confidence in your integrity and all necessity for further secrecy is about past, still I think for your own good, in view of possible happenings, it is best that I and my mission remain a mystery to you."

The captain turned toward his cabin as he spoke, as if to terminate the conversation.

"Perhaps it is not such a mystery after all, captain," said Harry, quietly. "We must be pretty near the coast of Cuba."

The man turned quickly, a glint of that fierce light in his eyes, and then he burst into a hearty laugh.

"Pretty sharp youngsters, eh, Suarez?" he said. "We may be able to make some use of them yet. I think they better dine with us to-night."