Suddenly the whole fabric trembled violently. The engines ceased firing, the propellers turning on a free axis under wind pressure only. Then, in less than five seconds, the motors "picked up" again and resumed their normal revolutions. Glancing downwards, Peter could see the mechanic had been aroused from his usual state of lethargy; for, in ordinary circumstances, he had little or nothing to do while the machine was in actual flight. Whether the engineer in charge of the after motors had been similarly startled Peter had no immediate means of finding out. But what puzzled the pilot was the brief duration of the "short". Uncle Brian had arranged for a sixty-seconds liberation of the polarizing rays. Without the shadow of a doubt, the momentary cutting out of the "juice" was owing to Uncle Brian's "gadget". Had one motor only faltered, Peter might have attributed that to known engine trouble; since all four were affected simultaneously, the phenomenon could only be put down to the mysterious rays. Peter Corbold was a fellow who always liked to get down to rock bottom, when dealing with a knotty proposition. He was still puzzling over the affair and trying to find a possible solution, when once again the motors ceased functioning. This time, the "cutting out" was definitely prolonged. Peter prepared for a vol-plane, elevating the wings to their maximum resistance in order to check the downward glide, the while circling to keep the flying-boat immediately over the expanse of lake. For all practicable purposes the machine was now a motorless glider without the power, owing to her weight and the limited area of the planes, to rise to a favourable air current. The best she could do was to fly horizontally for a few seconds and then glide earthwards. Sooner or later, unless the engines regained their power, the machine must come to rest on the surface of the water. The Rioguayan crew were now in a state bordering on panic. It was fortunate that Peter had taken the precaution to bolt the door between him and them, or his office would have been invaded, with disastrous results. Foiled in that direction, the Rioguayans could only stare helplessly, until the sight of the hare-brained Englishman coolly manipulating the planes and rudders helped to restore them to a state of passivity. All this occurred in the space of forty-five seconds. Peter was beginning to doubt whether he could keep up for the remainder of the stipulated minute when at a height of one hundred metres the motors fired again. "Well, that's proved the device, any old way," decided Peter, as he began to ascend again. "My insulation stunt is a dud, but I'm jolly glad it is." Another twenty minutes elapsed before the flying-boat landed at El Toro, for Peter was in no hurry, as he wished to restore confidence in his somewhat tremulous fellow-airmen. Uncle Brian was there to greet him.