AS the monoplane rose higher, Bob and Joe and the others waved to the little group below until it faded from view. Then they turned to take in the country they were passing over.

Streets, buildings, vehicles, and people were mere specks below, as Karl sent the machine to a new high altitude. Past the city of Washington, and then on—on above the many small cities and towns of southern Maryland.

“Wonderful view!” breathed Joe Lewis, gazing out at the wonderful panorama that was spread out before them.

“Bet we can see fifty miles,” added Bob. “There’s the Potomac River over there, and away off in the distance seems to be the ocean. I wonder if it is?”

Bob and Joe were strangely unaware of forward movement, though they were going nearly twice as fast as the fastest automobile. The comfortable enclosed cabin kept out the fierce roar of the wind, and heavy insulation silenced the noise of the engine to a remarkable degree. Thus they found it easy to carry on conversation.

They made the hundred-and-forty-mile trip to Norfolk in little more than an hour. Then, after leaving this city behind, they passed over North Carolina until finally the ocean loomed up before them.

When the last stretch of land had been left behind, Bob and Joe were thoughtfully silent. What if anything should happen while they were out here above the boundless water, with no place near on which to land? It was not pleasant to think of plunging hundreds of feet into the ocean, even though the water might be calm.

As they flew farther, Joe was surprised that they had not seen ships below them.

“This isn’t a route of travel,” explained Mr. Holton. “We probably won’t see any large liners till we get farther south.”

Later they were able to make out several tramp steamers, which, when viewed at that altitude, appeared to be at a standstill. Just where the vessels were heading the air travelers could only guess.

Suddenly, unexpectedly, the youths and the naturalists found themselves in a heavy cloud, which hid the ocean from view. It was so dark that Mr. Wallace almost mechanically switched on a light.

“Wonder if this means danger?” mused Joe, gazing intently out of the window at the haze.

“I was wondering the same thing,” came from Mr. Holton. “If it does, we ought to hear from Karl before long.”

But before long they passed out of the cloud and once more could see the ocean. But now the sun was nowhere in sight.

“We may have some rain,” said Karl through the telephone. “Be sure all the windows are closed tightly.”

Bob wondered if rain would be a hindrance to flying, although he hesitated to put the question before Karl. If the truth were known, he was not a little worried.

As they flew farther the sky became more overshadowed. Dark, threatening clouds hovered near, as if to warn the air travelers to seek a place of refuge. It was not a pleasant sight to the four passengers.

All at once they had a sudden sensation of falling, which almost took their breath away. It lasted but a brief moment, however, much to the relief of all.

“What caused that?” asked Joe, who had turned pale.

His question was answered a little later by Karl.

“Feel that drop?” the aviator asked. “I did that to see if we can’t get below the storm area.”

“How far did we fall?” inquired Mr. Wallace interestedly.

“Only a few hundred feet. And I steered over to the east, too. We seem to be out of the storm area.”

Now, as they flew on, the travelers could easily glimpse the dark mass of clouds that they would have been forced to pass through had they remained strictly on their course.

An hour or so before noon, the explorers caught sight of a little group of islands, and in the distance they could make out one that was much larger.

“We’re nearing the West Indies,” observed Mr. Wallace jubilantly. “That large island away over there is probably Abaco.”

As they neared the land, Karl dropped to perhaps a thousand feet. From this altitude they could command a good view of the country below them. It was for the most part wild and uninhabited. There was a great deal of fog hovering about, or they could have seen many more islands.

They were nearing the tropics, as evidenced by the mercury rising in the thermometer. As they were traveling evenly, it was safe to open the windows. The resulting gush of wind was at once greatly appreciated.

“We’ll have about three hundred and seventy-five miles of traveling before we reach Cuba,” announced Karl, as they passed over a large cluster of islands. “Maybe we’d better land there, at least for a few minutes. It’ll give the ’plane a chance to cool off, and then, too, we can look it over.”

It was three hours later that Bob caught sight of what appeared to be a long black line stretching out of sight to their left. That line gradually took shape and color, and the explorers found themselves nearing Cuba.

On the side nearest them was a large mountain, with a cone-like top that gave it the appearance of a volcano.

Within sight of this peak, Karl picked out a level stretch of ground and sent the monoplane downward. He found it necessary to make a spiral landing, as there was danger of otherwise striking a line of low, sharp peaks.

Bob and Joe watched closely as the ground came up to meet them. Then they felt the wheels bump, and they knew they were safe.

“All out!” called Karl, appearing at the cabin door. “That is, if you want to rest your legs.”

The others needed no urging. They climbed stiffly out of the ’plane and stretched freely. While they had not been cramped, they had nevertheless not been allowed the freedom of violent exercise.

“So this is Cuba,” observed Joe, yawning and looking at the green jungle, which seemed everywhere about them.

“Not much to be seen in this part of the island,” Mr. Wallace told them. “We’re at the extreme eastern end.”

They looked around a bit, though, to satisfy their curiosity.

When they finally returned to the ’plane, after taking a tramp toward the high peak, the explorers were ready to devour anything in the way of food.

Sandwiches and iced tea, the latter having been kept cold in a thermos jug, served as a meal, and proved to be very satisfying to the hungry explorers.

Then, after taking a short rest in the shade of the monoplane, they prepared to resume the journey.

“Now comes the worst part,” said Karl, with a frown. “We’ll have to fly for over five hundred miles without seeing a trace of an island. The Caribbean Sea may prove treacherous for tropical storms, too.”

Luck was with them the first half of their trip. The sky remained clear and light, not giving the slightest indication of a change of weather.

Then suddenly, when the travelers’ hopes were high, they noticed that the sky was becoming dark and threatening. A fierce wind was blowing with a dangerous velocity, which threatened to send the monoplane off its course.

Karl guided the machine off to the west, in the hope of passing beyond the storm area. He speeded up to over a hundred and fifty miles an hour, for he knew that whatever he did must be done quickly.

But try as he did, he could not escape the heavy clouds and terrible wind.

His hope almost gone, he sent the ship to a much higher altitude, thinking it might be possible to get above the clouds.

But it was too late. With a rush and a roar, the tropical hurricane was upon them.