"Now for a practical test of the ZZ-rays, Mr. Tregarthen," exclaimed Captain Brookes, as he bade Gerald farewell. "It is now 10.30 a.m. At noon punctually I shall liberate the electric current from the _Olive Branch_, at a distance of nine sea miles from yonder crag. You will please remain here, and on no account release the prisoners till my return, which, I hope, will be at 1.30 p.m." "Very good, sir," replied Gerald, with a salute, as the captain ordered the remainder of the landing-party to fall in. Meanwhile the divers had been working incessantly, and the propeller was again fit for its task; the anchor was weighed, and the _Olive Branch_ once more glided down the waters of Desolation Inlet. Left in charge of the prisoners Gerald had ample time to reflect upon the action he had taken. In his anxiety to save the savages from extermination he had made a somewhat hasty proposal; and now, with the execution of his plan in progress, the force of Captain Brookes' objections came home to him. The hitherto untried ZZ-rays might prove themselves far more destructive than their inventor claimed; their radius of action might overlap the area governed by those sinister chequers on the indicator; the distance and direction of the pinnacle from the _Olive Branch_ might be misjudged--and then? Tregarthen glanced at his watch. It was a quarter to twelve. "Smith!" he called out, addressing one of the petty officers. "Sir?" "Pass the word for the men to take off their bandoliers, empty the magazines of their rifles, and stow the cartridges under yonder tree." Without betraying his surprise at the unusual order the man hurried off to communicate Gerald's instructions. Implicit obedience was Smith's sheet anchor. "There, I've taken every possible precaution," mused the young officer. "Now things must take their course." As the minutes slowly sped the tension amongst the seamen increased. Even the savages seemed to have an inkling that something extraordinary was afoot. Watch in hand Gerald waited till the long hand pointed at a minute to the hour. "Look!" he shouted, pointing to the distant crag. The natives, although they did not understand the word, followed the direction indicated, and a tense deathly silence seemed to fill the air. Precisely at noon a terrific detonation shook the ground, and a thick cloud of dust and smoke obscured the view of the pinnacle. When the cloud had dispersed the rock had completely vanished, only a heap of boulders marking its position.