"Chiefly as a matter of precaution. The slightest defect in a terminal, switch, or wire might throw the whole of the electrical apparatus out of gear. But there is another danger I have to guard against--the danger of annihilation from the sky. This device you see here has taken me fifteen years of unremitting toil and thought to perfect, and perfected it is as far as my original plans were concerned. But within recent years the advent of the airship and aeroplane has tended to revolutionise warfare. In order to negative the possible ill results of the ZZ-rays to the vessel that releases them the indicator board is arranged so that the minimum range is nine miles. Thus I can put a vessel out of action at any distance between nine and eighteen miles. The Z-rays, having a comparatively low electro-motive force, can be brought into play at a distance of two miles, without danger to the _Olive Branch's_ delicate mechanism. It consequently follows that to use the rays within the distance of 1,000ft.--the effective range of an airship--the consequences would be disastrous to us. I therefore have to rely on other means. Now I think I have explained the contents of the conning-tower pretty fully, so we will resume our tour." "But what are these for?" asked Tregarthen, pointing to a triple row of metal studs fixed to a mahogany board on the side of the conning-tower. "To control the gun fire. When the ordnance is installed I'll explain their use. But we will now ascend to the flying bridge." With the wind howling over this exposed position like a veritable tornado Gerald was glad to gain the shelter of a diminutive chart-house. Here was the electrical steering apparatus, but, to his unbounded astonishment, Tregarthen found that the place was untenanted, the only other occupants of the bridge being a lieutenant and a seaman, both of whom, glass in hand, were scanning the horizon. "Don't you keep a hand at the helm?" he asked. Captain Brookes shook his head. "Not on long ocean voyages," he replied. "The ship steers herself. Like plenty of other problems, it's simple when you know how. The _Olive Branch's_ steering apparatus is on the same principle as that of a Whitehead torpedo. The course is set by means of a pointer on the compass-card. The slightest deviation causes a small valve to be opened which actuates the rudder. Of course in confined waters or on going into action we use the steering-gear in the conning-tower." "I can scarcely grasp the meaning of these wonders," remarked Tregarthen. [Illustration: chapter VII] CHAPTER VII RUMOURS OF WAR "ONE moment, sir," said Gerald as he accompanied the captain across the fo'c'sle, where a party of men were undergoing musketry exercise. "What is the meaning of that cylinder close to the muzzles of the rifles?" "It's a silencer--the Lucas silencer, to be exact. I took a fancy to the device and acquired the patent. Mr. Ball, bring me one of those rifles, please."