And now the daring joy-riders, keenly watched by hundreds of eyes far down below, left the shore once again, and the naval harbour with its shipping, and headed for the French coast, watching the surface of the sea as though they would read its secret. "East-south-east, Dastral! That's the course till we sight the opposite shore," shouted Jock to his comrade, who, he thought, in his excitement and eagerness to spot a submarine lurking in the depths, might miss his way, as many a brave aviator before him had done. "Right-o!" came the answer to this reminder, for the French coast was hid as yet in the morning mist. Then the course was altered slightly once again, in order to make a proper landfall on the other side. They were flying low now, much lower than the usual regulations permitted, for it is necessary to keep a good altitude in crossing the Channel, not only because of the chance of running into a stray air-pocket, but to enable one to 'plane to safety should anything go wrong with the engines, for only a seaplane can ride the waves like a ship; and this was no seaplane they were riding to-day. Far down below them they could see the patrol boats hunting for their prey. They could also see the mine-sweepers at work, clearing the fairway from those foul nests of floating mines which the crafty foe had been busy laying with their submarines. Once or twice they thought they could make out some dark-grey object like a mine or sunken vessel beneath the surface of the water. A string of mine-sweepers were stretched out below them now. They could see them distinctly, could see even the long nets that trailed between them, for the sun was gaining power and the morning mists were rolling away. The grey expanse of water took on another hue, changing from a dull grey to a greenish tint, with patches here and there of deep blue, where the water deepened, or the surface of the mirror reflected a corresponding patch of the azure above. Keenly now they searched the face of the deep for any dark speck, for, from an aeroplane, it is possible to look far down, often even to the bed of the sea; but as yet they saw nothing, save an occasional piece of wreckage, which had probably detached itself and floated from the treacherous Goodwins, away to the eastward and the northward--those treacherous shoals which hold the remains of so many gallant barques and vessels, from the Roman galley to the modern liner. They had not long left the mine-sweepers on their port quarter when Jock, through his glasses, noted something like a string of porpoises, which, owing to the motion of the waves, appeared to be travelling along. They seemed so regular and orderly in their movement, however, that he was about to pass them over. Thinking, however, that he would like to call Dastral's attention to them, he shouted:--