Hastening back to the control compartment, Peter found that the for'ard motors were now firing spasmodically. In a few moments they would cease functioning for lack of fuel, and then there was nothing to keep the flying-boat from descending with fair rapidity. Her weight and relatively small plane-area were against her for prolonged gliding. He touched his uncle on the shoulder and motioned him away from the controls. "Luck's out this time," he said grimly. "It's a thundering big drop in the dark." CHAPTER XVI "Crashed" Peter had barely resumed charge, when the motors coughed and stopped. A deadly silence succeeded the purr of the engines, since the rush of air past the metal planes was inaudible within the sound-proof compartment. It was the pilot's chief concern to keep the flying-boat up as long as possible. It was entirely beyond reason to suppose that the gliding would be prolonged till dawn, but the longer the aircraft kept up the better, since there would be more time to make preparations for the forced landing. Planing as nearly in a horizontal direction as possible for two minutes, was followed by a short steep rise until the flying-boat seemed in danger of "stalling". This manoeuvre Peter repeated, knowing that for every hundred feet of vertical drop he could knock off twenty or more by the sudden leap against gravity. For quite twenty minutes he held on, his hand dexterously manipulating the controls, while his eyes never left the altimeter and speed-indicator. Meanwhile, Brian Strong was busy. Realizing that perhaps the flying-boat might be able to land on fairly even ground, he set about to prepare the electric head-lamp which could be trained in a vertical arc of fifteen degrees--enough to illuminate a sufficient length of ground before the machine came in contact with _terra firma_. The searchlight was of the accumulator type. According to instructions issued to the Rioguayan airmen the batteries were to be kept fully charged; but when Brian tested the circuits he found that the accumulators had completely run down. There remained the secondary head-lamp--a three-hundred candle-power acetylene-generated light. Hoping against hope that this apparatus was in working order, Brian unfastened the lid of the generator. The acetylene chamber was full of perfectly dry carbide, but the water compartment was empty. "How long can you give me?" asked Uncle Brian. "Five minutes--ten, with luck," was the reply. Hurrying to the water-tank, Brian turned the tap. There was no flow. "Has every tank in this confounded contraption run dry?" demanded Brian. Then the solution of the mystery dawned upon him. The water in the tank was frozen into a solid block. Had the motors been water-cooled a way out of the difficulty would have been simple; but being air-cooled no help was forthcoming from them.