Madden thrust head and shoulders into his float, a round canvas-covered hoop of cork, and set off at an easy stroke. Now that he was flat on the water, he could no longer see the lanes of seaweed, and he would be forced to depend entirely upon signals from the dock.

Alongside Madden came Greer, and after them Caradoc. Like all Americans, Leonard gradually increased his energy, and forged ahead at a rate considerably faster than that required for long distance swimming. Once or twice Caradoc warned the swimmers to go more slowly, and at each monition Madden slowed up a trifle, but within a few minutes he would again speed up unconsciously.

The three swimmers could form little idea of the rate they were making in the lifeless sea. At the end of half an hour, when Leonard looked back at Hogan on the wall for signals, the dock still loomed above him, a vast glare of red in the dazzling sunshine. It seemed impossible to get away from it; the featureless red flare followed him as a mountain peak seems to follow a traveler.

The sun beat oppressively on his head and blistered his shoulders through his net undershirt. The warm water soaked the energy out of limbs and arms. He changed from breast to over-arm stroke, then he shifted to the crawl and trudgen stroke.

"Perhaps we'd better rest awhile, sir," suggested Greer, who came puffing close behind.

"Beastly hot, this sun," Leonard ducked head and shoulders under water for relief. His hat floated off and he grudged the slight effort to retrieve it.

"How far are we?"

"Dock looks as close as ever—where's Smith?"

Greer nodded toward a small head and shoulders bobbing behind a little white buoy.

At that moment, they heard the Englishman's voice calling, "To the right!"

The boys turned and struck out ahead once more. They regretted having to leave the straight line. As far as they could see there was no algae in sight, the water was one glassy blue. And the mysterious schooner, with its lights and shadows exaggerated in the tropical glare, seemed to the tired swimmers to be as remote as ever.

As Madden pressed on and on, changing strokes after the fashion of tiring swimmers, the constant beat of the sun made his eyeballs ache; the ocean felt like a Turkish bath; the muscles in his shoulders, back and legs grew numb, with an occasional cramping twinge. And what irritated him as much as anything else was the fact that he was swimming toward the right quarter of the schooner, throwing away his energy.

Just then Caradoc gave a distant call, "To the left."

With deep relief, Madden rounded back toward his goal. He had swung about some unseen cape of algae. He looked back toward the dock. Hogan, a very tiny figure, held his flag straight up; that meant "dead ahead."

In relief Madden turned over on his back, laid his hat across his face, then with hands resting on chest, he began sculling along with knees and feet.

He did not know how long he swam in this fashion. Queer ideas drifted through the lad's mind. He recalled standing on the bridge of the dock as it went out of the Thames and wondering what would happen. He had never anticipated anything like this. It seemed that he had been swimming for days and weeks. He reminded himself of those little kicking toys that never get anywhere. He felt as if he were a June bug buzzing helplessly at the end of a string. He kicked, kicked, kicked under the broiling sun, in the hot water. The sweaty smell of his hat band disgusted his nostrils. The crown of his hat seemed to coop the heat over his face, sweat seeped into his closed eyelids and stung his eyes. He gave his head a little shake. The buoy slipped out and he bobbed under the tepid water head and ears.

This jerked him out of his dreamy state. He whirled over, struck to the surface, spat out brine, blinked his eyes. Somebody was shouting something in an urgent voice. The noise buzzed in his waterlogged ears.

"Hey, hello! What is it?" he cried, giving his head a shake and putting on his hat.

"School of sharks!" shouted Greer, coming toward his leader at a foamy speed.

"School of sharks!" echoed Madden with a sharp thrill. "Where? Which way?"

"Must be toward the dock, sir!" panted Greer driving up.

"Where's Caradoc?"

"Yonder." He pointed toward a distant twinkle in the water.

"We must get together—yell to him, warn him!"

The two lads began a strenuous chorus that further used up their exhausted strength. Caradoc responded by a wave of his hand. Then when he understood "sharks" he gathered speed in their direction.

By this time the dock seemed as far away as the schooner, and was in reality probably farther. On the wall of the dock, they could see Hogan's microscopic figure apparently having a fit, against the coppery sky. No doubt from his height he could make out the monsters. Perhaps Hogan could see the great fish shooting along with sinister, exertionless ease toward these clumsy adventurers—a school of trout striking at three awkward beetles.

"Hey, Caradoc! Caradoc!" screamed Madden. "Straight for the schooner!" The American stared around with tense nerves for the little swishes on the surface that betray the attack of a shark.

From something near middle distance, the Englishman raised a hand toward his comrades and motioned them forward.

"Go on! Go on!" he gasped in a tired voice. "I'll catch you!"

Indeed, there was little to be gained from waiting. Caradoc moved toward his friends with a long overhand stroke that gave him the queer appearance of some huge water bug striding along. Madden and Greer propelled themselves slowly toward the schooner, waiting for their friend to close up. They could not keep their eyes off the Englishman. Every moment they expected to see him jerked under, or they expected to see a huge shadowy form strike at themselves through the clear green water.

Once Madden looked at the dock. Hogan on the rim of the red flaring wall was flinging out all kinds of despairing gestures.

By this time Caradoc was in hailing distance.

"Did you say sharks?" he called out in a dull voice.

"Yes, sharks!"

"Where a way?"

"Don't know!"

At that moment a trickling thrill went through the American. A long dark motionless shadow lay in the water straight in front of him. He stopped swimming suddenly.

"Stop, Greer! Straight ahead!" he warned in a low tone, easing himself carefully up on his buoy for a better look.

By this time the swimmers were nearly together and all three stared ahead with painful intentness.

"That dark thing?" inquired Greer in an undertone,

"Yes, we ought to have a knife apiece."

"I never saw a shark lying still," panted Caradoc straining his eyes.

"Say, that's a little streak of seaweed," decided Farnol, beginning to move toward it.

Then all three perceived it was merely seaweed. The shark-like illusion disappeared completely the moment someone doubted it.

"Who cried out sharks anyway?" demanded Smith of Madden.

"Greer there warned me—he yelled 'school of sharks.'"

"Where did you see them?" inquired Caradoc of Farnol.

"You shouted school of sharks to me yourself," defended Greer.

"I! I!" puffed Caradoc, whose spurt had blown him badly. "I said nothing about sharks!"

"Well, what did you say?" demanded Greer.

Caradoc thought back fretfully. "I said we were running into a cul de sac."

"A cool de sock!" repeated Greer with irritation. "What did you want to say 'cool de sock' for?"

"I was calling to a gentleman," panted Smith with an edge of temper in his tone, "and here you've swung us clear off our bearings because you didn't know a common French phrase——"

"French! I'm no Frenchman! Why don't you talk English!"

The two tired, worried, overheated men were rapidly brewing a quarrel, when Madden interrupted.

"Look how close we are to that schooner! If somebody would raise another shark alarm, we'd land plump on her decks."

"Yes, but this Zulu here has run us straight into a loop of seaweed it'll take two hours' swimming to get out of—cul de sac, school of sharks! Why the two phrases scarcely resemble each other!"

Madden turned longing eyes toward the motionless schooner that was not more than three-quarters of a mile distant. "Say, it's too bad to turn around and swim away from that vessel!" he lamented wearily, "and this sun is fierce!"

"I say let's try going through!" encouraged Greer.

"It'll be—difficult," warned Caradoc.

"Won't swimming clear around the earth be difficult?" demanded Greer hotly.

"Proceed," agreed Caradoc tersely. "It's all one to me."

The boys adjusted their floats and once more began their weary labor, all three disgruntled at the false alarm. As they worked their way forward, clumps of seaweed, similar to the first they had seen, thickened in their path. After a long swim in and out, they reached a point where these floating masses coalesced into an island, or a continent, that swung far back toward the barge in the segment of a great semicircle. Fortunately there were still open channels in this main field, and one of them led toward the schooner. They struck out up this estuary, which presently became so narrow that they were forced to travel single file. Occasionally their kicking feet would strike slimy filaments in the water, but for a while the channel cheered the swimmers, for they could now see they were making progress toward the ship.

Ten minutes later, however, they reached the end, and an inexorable continent of slime lay between them and their goal. Madden paused in the last yard of clear water, hung to his buoy, his big biceps flattened on the canvas cover and slowly blistering in the sun.

"All right, boys, close up," he panted; "let's stay in helping distance of each other."

"Shall we try to take our buoys through, sir?" inquired Greer.

"We'll start with them."

"Don't try to use your legs in the weed," warned Caradoc. "Don't kick; you'll get tangled."

"We'll experiment and work through the best way we can. If it turns out too bad, we can turn back, that's one consolation."

Just then, under Madden's astonished eyes, a queer thing happened. The long open tongue of the sea which they had just entered, silently closed up. It seemed to close very slowly, and yet it was accomplished in an amazingly brief time. Some dull movement in the Sargasso current had blocked the adventurers with sinister precision. Madden felt the hot slimy mass close softly around him.

It was now as easy to go forward as to return.