There was a rush like a pack of black water spaniels going after a thrown stick, but the boys had been tricked too often by passengers stopping at Aden in the regular steamers, and they did not go far, but turned round, treading water and shouting. "Come back then," cried the doctor. "Here, close to the yacht." In all probability the boys did not comprehend a word, but the gestures made with the hand containing the shilling brought them all back, and they ranged themselves in a line close in, and shouted and splashed away till the doctor, whose left hand had been in his pocket, threw the shilling shining and twinkling through the sunny air as far as he could. Away went the boys with a tremendous rush, making the water foam, and naturally the biggest and strongest took the lead, leaving three little fellows well behind. The doctor had anticipated this, and drew their attention with a shout, at the same time holding up another shilling, and as they turned to swim back, he suddenly dropped the coin about six feet away from the yacht's side, where the water was still. _Plop_! down went one little fellow, who rose up, turned over, sent his heels gleaming in the sunshine, and disappeared, as _plop! plop_! down went the two others. "Just like a lot of dabchicks," cried the doctor; "now we shall see them race for it. See the shilling, Jack?" "Yes; here it goes." "Yes, and here they come. Look at them. Why, they go down faster than the coin. It's wonderful." Wonderful it was, for the dark little figures glided through the crystal water like seals, and every motion could be followed till the coin was reached and ceased to twinkle as it sank. Then once more the dark figures grew plainer and rose and rose, but somehow more and more astern, and Jack looked startled. "Why, there must be a tremendous current here," he cried. "They're being swept away. A boat! a boat!" The doctor looked as much startled as his companion, but a very gentle vibration enlightened them the next moment, for the engine was once more in motion, the screw revolving slowly, and the _Silver Star's_ prow was gradually coming round in answer to the helm, till she pointed straight for the open sea, where the throbbing and quivering of the vessel increased as she went easily ahead, and then faster still over the perfectly calm water, for there was not a breath of air.