concern, therefore, was for the tramp steamer surging up Channel, and nearing the end of her long voyage from Valparaiso to London. At all costs to the aeroplane, she must be saved from the deadly mines towards which she was now heading directly. The tide was with her, and she was coming up rapidly. In another five minutes she would be in the cunningly laid trap.

For the moment, Dastral continued to circle over the mine bed, hoping thereby to warn off the tramp. Of this she appeared to take no notice, though undoubtedly a score of eyes were watching his gymnastic gyrations from the deck and bridge of the vessel.

"Try the gun, Jock. Quick!"

"Rip-r-r-r-r-r!" went the Lewis gun, as Jock pressed the button and fired off half a drum of ammunition.

Even yet, the tramp steamer did not seem to understand, for her captain did not charge her course.

"Is she fitted with wireless?" yelled Dastral.

"Yes," answered the observer, putting down his glasses into the socket for an instant.

"Then give her a message on the international code. It's her last chance. She'll be on the infernal things in another two minutes."

"Right-o! Here goes!" and, uncoiling the long aerial wire, he tapped out just one word on the sending key:--

"M I N E S!!!"

"Good. If that fails, the ship's done for!" ejaculated Fisker, as he watched eagerly for the ship to change her course.

On came the vessel, quite oblivious of the danger. She was less than a cable's length from the string of mines, and still steaming fast, when Dastral noted some movement about the deck, where a dozen or so of the crew stood just for'ard of the bridge, in the waist, gazing intently at the 'plane.

"Heavens! It's too late!" gasped the pilot, as he saw the steamer's bows running dead on towards the very centre of the floating mines.

"No, she may just do it," he ventured to his observer, as he saw the sudden commotion on board.

Suddenly, out of the wireless room, the operator, evidently carrying the message, dashed up the companion way to the bridge, flourishing a piece of paper in his hand, and shouted:--

"Mines in the vicinity, sir!"

Then it was that the captain realised the danger he was in, for the mine-sweeper coming up on the starboard bow was also flying the signal for her to heave to.

Dashing to the wheelhouse door, a few paces away from where he had been standing, the captain shouted to the man at the helm,

"Hard-a-starboard!"

And though the tide was with her, the good ship swung round smartly, only in the very nick of time, for, as she turned, one of the deadly mines was within two feet of her stern, and the wash from her screw and the rapid movement of her rudder as she came round, caused the nearest mine to come into contact with a piece of wreckage, at which there was a terrific roar, and a huge column of water was lifted up and hurled some two hundred feet into the air.

Then followed a more terrible spectacle, for one after another the whole string of mines went off, as though they had been countermined. It was just as if there had been a sub-aqueous earthquake, for a prolonged roar of thunder, earsplitting and nerve-racking, immediately followed, while the sea for hundreds of yards around rose up like a huge waterspout, and for some minutes the whole surface of the water, hitherto placid, broke into tumultuous waves.

The tramp steamer received fifty tons of water upon her decks, but save for a slight starting of the plates in her stern, she was untouched. Nevertheless, she had to keep the pumps constantly in use for the remainder of her voyage.

After circling round the spot for another few minutes to speak with the Commodore of the fleet of mine-sweepers, Dastral turned the hornet's head once again towards the enemy's coast, and the captain of the tramp steamer dipped his pennant and gave a long blast on the siren, as a token of gratitude for the service rendered.

The aviators were well pleased with themselves for the part they had taken in the little adventure, which had not been without its thrills, and a spice of danger.

They were now almost in mid-Channel, and could see both shores. There were the white cliffs of Old Albion behind them, while in front, a little on their left, Cape Grisnez rose out of the water. Below them several liners, transports and colliers, could be seen making either up or down Channel, or for one of the ports on the English or French coasts. Turning round to Fisker, the pilot shouted through the speaking tube:--

"Sorry it wasn't a German submarine, old fellow. There'll be no D.S.O. for us for picking up a string of floating mines."

"Ah, well. Better luck next time," called back the observer.

"The place is too well patrolled now for the Huns' submarines to show themselves about here. Gemini! but I'd give my brevet and six months' pay to spot one this journey. It would be some find."

The observer did not reply immediately. He was keenly searching the opposite shore to find the breakwater at the entrance to Boulogne harbour.

"Can you see it yet?" called the pilot, noting an anxious look on Jock's face. "Yes," replied the latter. "Better give her another two points south, and then we shall just about hit the canal below the town. Our instructions were to follow it to the main aerodrome."

"Aye, aye," answered the pilot, altering the controls slightly, and bringing her head round upon a more southerly course.

Shortly after this, the town and harbour of Boulogne came into full view to the naked eye. Their intention was to leave it a little on their left, and, then making a landfall of a certain railhead and canal, take a short cross-country flight to the big aerodrome behind the British lines. They now began to regard themselves as nearly at the end of their journey, and had no expectation of a still greater adventure before them--an adventure which would prevent them reaching their destination, at any rate, that day.

Only some five or six miles of sea now lay between them and the land, and they were right over the track of the transports, which made a continuous line of traffic between the two shores, when Fisker, who had taken up his glasses again in order to watch a batch of troopships, escorted by a couple of destroyers, suddenly turned them on to a large four tunnelled hospital ship, which, coming out of the harbour, crowded with wounded and war-worn men, was ploughing its solitary way towards Old Blighty, without any other escort or protector than the Red Cross flag.

Suddenly, as he watched the stately vessel moving along at twenty-five knots, with the huge combers falling away from her bow, and a long milk-white trail from her stern, he started suddenly, and lowered his glasses, almost shrieking at the top of his voice:--

"See there, Dastral! Quick!"

"Where away?" cried the pilot, turning round sharply, and catching a glimpse of Fisker's horrified face.

"There!" exclaimed the observer, laconically, pointing with his hand in the direction of the hospital ship.

Dastral looked in the direction indicated.

"The brutes!" he gasped. "Not if I can prevent it."

That which had called forth these horrified expressions was nothing more or less than a lurking German submarine, hidden beneath the water, but with a few inches of periscope above the surface, manoeuvring to bring the huge hospital ship within its range. It had evidently watched the procession of transports pass by, but, fearing that it might be rammed by one of the destroyers if it revealed its presence, it had waited for some other tasty morsel to come along. Unfortunately, there was nothing she could touch but this hospital ship.

With any other nation, a vessel flying the sacred emblem of humanity, which floated from the masthead of the ship, would have been immune from attack. But to the Hun no code of morals seems to hold good. Nor was any crime to be regarded as such if only some damage could be inflicted upon the enemy.

"Ach,