"Simply that as soon as the vessel is outside the Breakwater I mean to take the 'Aphrodite' into the Hamoaze, and give you a chance to see that historic stretch of water under slightly different conditions from that which you have been accustomed to, Mr. Hythe. You were in the submarine service, I believe?"

"Yes," a.s.sented the sub. "But how do you know that?"

"Merely by a reference to the Navy List. But look ahead; see that object dead in line with our bows?"

"An electro-contact mine, by Jove!" exclaimed Hythe.

"Right again. Since the beginning of this German war-scare, which I venture to predict will pa.s.s away, unless my powers of reasoning play me false, the approaches to all British ports of any magnitude, especially the naval ones, have been strewn with these contrivances. Watch."

A slight touch on the switch controlling the helm and the "Aphrodite"

swung away to starboard, clearing the deadly mine by less than twenty feet. Another loomed up ahead, only to be avoided by another touch of the helmsman's finger.

"I do not want to boast," remarked Captain Restronguet, "but I have enough electrical energy stored within this vessel to explode simultaneously every mine, be it a mechanical, observation, or electro-contact one, in Plymouth Sound, and even seriously imperil every fort and ship in the vicinity. Some day I may have to put the powers at my command to a stern test, but until the necessity actually arises I prefer to exploit the 'Aphrodite' solely as an example of what I am capable of producing in the interests of science. Look out of that scuttle on your left; what do you see?"

"A regular pile of huge stones," replied the sub.

"The eastern extremity of that wonderful work known as Plymouth Breakwater. We are now in only forty-five feet of water allowing for the state of the tide. The top of our conning-towers are but fifteen feet above the surface, yet I can a.s.sert with confidence that anyone standing on Staddon Heights and looking down upon this channel from an alt.i.tude of not less than three hundred and fifty feet would not see the faintest sign of the 'Aphrodite.'"

"What causes her to be almost invisible?" asked Hythe. "Are her plates made of or faced with gla.s.s?"

"Oh, no. Gla.s.s would not serve the purpose. The light would be reflected too much. In fact the 'Aphrodite' would be a huge heliograph, sending out rays of reflected sunlight in all directions. The composition placed over the steel plating of this submarine is a secret.

All I can say at present is that it has the power to reflect the image of near objects only. It absorbs all brilliant rays of light, and is in consequence an almost perfect form of invisibility."

"What is that?" asked Hythe excitedly, pointing to a sudden turmoil in the water ahead.

"Only the action of the triple propellers of a torpedo-boat-destroyer.

We are overhauling her. Ease down to ten knots, Carnon. She's off through the Asia Pa.s.s. There's not enough water for us; so let her come round to starboard."

The quartermaster telegraphed for speed to be reduced; the submarine turned towards the deeper Smeaton Pa.s.s, leaving the destroyer, in blissful ignorance of the proximity of the much-searched-for Captain Restronguet, to take the short cut into the Hamoaze.

"Now we can take things more easily," observed the captain after awhile.

"The channel is now ninety feet deep, although we are but a few hundred yards from Plymouth Hoe. We are now approaching the Drake Channel, between the Victualling Yard and Drake's Island."

"However do you contrive to find your way about in a complicated waterway like this?" asked the sub, who was well acquainted with the above water navigation of that part of Plymouth Sound within the Breakwater. "You have no periscope?"

"A periscope would soon give the show away," observed his companion.

"For the present, we simply rely upon the chart and compa.s.s, and look out for the sudden shelving of the bottom. See, there! Hard a starboard, quartermaster: there's the Vanguard Bank dead ahead."

From almost due south the "lubber's line" in the compa.s.s-bowl pointed to almost due north. The "Aphrodite" had reached the "Narrows" between the Devil's Point and Cremyll.

At a word from Captain Restronguet the quartermaster set the engine room telegraph indicator to stop; another movement, a gentle hiss betokened the admittance of water into one of the sub-compartments of the vessel.

Then slowly and mysteriously the "Aphrodite" sank in twenty-two fathoms of water to the bed of the narrow channel.

At that depth, and owing to the swift-running tide, charged with the mud brought down by the River Tamar, the water was so thick that, till the electric lamps were switched on, the submarine was in total darkness.

"Prepare to anchor," ordered Captain Restronguet through a telephone.

"Good!" he e.j.a.c.u.l.a.t.ed, after about a minute had elapsed. "Now, Mr.

Hythe, you must be feeling hungry; so will you do me the honour of having lunch in my cabin?"

CHAPTER VIII.

EXPLANATIONS.

"By the by," observed Captain Restronguet, as he entered the cabin, "I have already sent a rea.s.suring message concerning you to the British Admiralty."

"You have! How?" asked Hythe in astonishment. "You are not fitted with wireless?"

"And why not? As a matter of fact we are; with one of the latest type of Raldorf-Holperfeld instruments, which, as you know, do not require out-board aerials. The message is received by an automatic recorder."

"And, might I ask, with whom do you communicate?"

"That need not be kept a secret from you, Mr. Hythe."

"Why not, sir?"

"Because I wish to detain you on board the 'Aphrodite' until I have no further use for secret correspondents. My wish is law, Mr. Hythe, and please to remember that. At the same time I wish to make your period of enforced detention pa.s.s as pleasantly as possible, and you will have complete facilities, up to a certain point, of gaining valuable information that will in time to come amply recompense you for any slight inconvenience that might arise."

"But my career? Remember, sir, I'm a naval officer."

"Of course. That is one reason why I think fit to keep you. Had you been an ordinary or even an able seaman, I should have taken the first opportunity of putting you ash.o.r.e, with hardly any chance of your seeing anything on board the vessel that might be put to my disadvantage. As soon as I learned that you were a naval sub-lieutenant I made up my mind to retain you as my guest for awhile."

"Then you are going to release O'Shaunessey?"

"Not at present. He, too, will serve a good purpose. He will be able to corroborate my statement that you will be honourably treated."

"But that will be unnecessary. Surely my word----"

"I have every confidence in the word of an officer and a gentleman, Mr.

Hythe. But my proposals are rarely influenced by circ.u.mstances other than the workings of Providence. You asked me a question concerning my sh.o.r.e agents. The answer is this: so long as the Government bestows licences upon private individuals to dabble in wireless telegraphy experiments it is a simple matter to keep in touch with events ash.o.r.e.

My princ.i.p.al agent lives in Highgate. He is a skilled operator, but he has contrived to keep his capabilities masked under the role of a harmless amateur. By advancing or r.e.t.a.r.ding the spark of the powerful coil of his instrument he can 'tap' any messages, whether from British or foreign warships, within seven hundred miles, while on occasions he has accurately read messages from Cape Race. Of course, most of the naval messages are in code, and are unintelligible to the uninitiated.

Nevertheless I can learn all outside news from this particular agent even when in the Mediterranean. For short distances we make use of wireless telephony, and by this means I can communicate with trusty agents in Devonport, Portsmouth, Sheet-ness and Chatham, and under certain circ.u.mstances with Rosyth and Dundee."

"Why did you come to a standstill here?" asked the sub.

"To partially recharge our acc.u.mulators. Our motive power is electricity. My invention in that direction is a revolution in marine and submarine propulsion. We are now anch.o.r.ed."

"Anch.o.r.ed?" echoed Hythe. "How? I saw no anchors when I examined your vessel from the outside."

"Anchoring, as we understand the term, consists of allowing the 'Aphrodite' to settle on the bottom of the sea. By lowering four steel plates, inclined at an angle of forty-five degrees--the acute angle facing aft--an almost irresistible brake, something after the principle of the spade recoil brake of the French quick-firing field guns, is formed. At this moment the ebb tide is swirling past at four knots.

The force of the current is turning our propellers, which, acting for the time being on subsidiary shafting, drive the dynamos that in turn replenish our acc.u.mulators."

"Then that means that every day you must recharge? How do you manage when there is not sufficient tide to actuate the propellers?"