I did not agree with those who have said there is no difference running submerged or on the surface. Under way on the surface was one thing.

But when we dived it was most unpleasant. I had been rea.s.sured at the start when I heard that there were ten compressed-air tanks under a pressure of two thousand pounds to the square inch. But only once before had I breathed compressed air and that was when one of our cases once took us down into the tunnels below the rivers of New York. It was not a new sensation, but at fifty feet depth I felt a little tingling all over my body, a pounding of the ear-drums, and just a trace of nausea.

Kennedy smiled as I moved about. "Never mind, Walter," he said. "I know how you feel on a first trip. One minute you are choking from lack of oxygen, then in another part of the boat you are exhilarated by too much of it. Still," he winked, "don't forget that it is regulated."

"Well," I returned, "all I can say is that if war is h.e.l.l, a submarine is war."

I had, however, been much interested in the things about me. Forward, the torpedo-discharge tubes and other apparatus about the little doors in the vessel's nose made it look somewhat like the shield used in boring a tunnel under compressed air.

"Ordinary torpedo-boats use the regular automobile torpedo," remarked Captain Shirley, coming ubiquitously up behind me. "I improve on that.

I can discharge the telautomobile torpedo, and guide it either from the boat, as we are now, or from the land station where we were last night, at will."

There was something more than pride in his manner. He was deadly in earnest about his invention.

We had come over to the periscope, the "eye" of the submarine when she is running just under the surface, but of no use that we were below.

"Yes," he remarked, in answer to my half-spoken question, "that is the periscope. Usually there is one fixed to look ahead and another that is movable, in order to take in what is on the sides and in the rear. I have both of those. But, in addition, I have the universal periscope, the eye that sees all around, three hundred and sixty degrees--a very clever application of an annular prism with objectives, condenser, and two eyepieces of low and high power."

A call from one of the crew took him into the stern to watch the operation of something, leaving me to myself, for Kennedy was roaming about on a still hunt for anything that might suggest itself. The safety devices, probably more than any other single thing, interested me, for I had read with peculiar fascination of the great disasters to the Lutin, the Pluviose, the Farfardet, the A8, the Foca, the Kambala, the j.a.panese No 6, the German U3, and others.

Below us I knew there was a keel that could be dropped, lightening the boat considerably. Also, there was the submarine bell, immersed in a tank of water, with telephone receivers attached by which one could "listen in," for example, before rising, say, from sixty feet to twenty feet, and thus "hear" the hulls of other ships. The bell was struck by means of air pressure, and was the same as that used for submarine signalling on ships. Water, being dense, is an excellent conductor of sound. Even in the submarine itself, I could hear the m.u.f.fled clang of the gong.

Then there were buoys which could be released and would fly to the surface, carrying within them a telephone, a light, and a whistle. I knew also something of the explosion dangers on a submarine, both from the fuel oil used when running on the surface, and from the storage batteries used when running submerged. Once in a while a sailor would take from a jar a piece of litmus paper and expose it, showing only a slight discolouration due to carbon dioxide. That was the least of my troubles. For a few moments, also, the white mice in a cage interested me. White mice were carried because they dislike the odour of gasoline and give warning of any leakage by loud squeals.

The fact was that there was so much of interest that, the first discomfort over, I was, like Kennedy, beginning really to enjoy the trip.

I was startled suddenly to hear the motors stop. There was no more of that interminable buzzing. The Z99 responded promptly to the air pressure that was forcing the water out of the tanks. The gauge showed that we were gradually rising on an even keel. A man sprang up the narrow hatchway and opened the cover through which we could see a little patch of blue sky again. The gasoline motor was started, and we ran leisurely back to the dock. The trip was over--safely. As we landed I felt a sense of gladness to get away from that feeling of being cut off from the world. It was not fear of death or of the water, as nearly as I could a.n.a.lyse it, but merely that terrible sense of isolation from man and nature as we know it.

A message from Burke was waiting for Kennedy at the wharf. He read it quickly, then handed it to Captain Shirley and myself.

Have just received a telegram from Washington. Great excitement at the emba.s.sy. Cipher telegram has been despatched to the t.i.tan Iron Works. One of my men in Washington reports a queer experience. He had been following one of the members of the emba.s.sy staff, who saw he was being shadowed, turned suddenly on the man, and exclaimed, "Why are you hounding us still?" What do you make of it? No trace yet of Nordheim

BURKE.

The lines in Craig's face deepened in thought as he folded the message and remarked abstractedly, "She works all right when you are aboard."

Then he recalled himself. "Let us try her again without a crew."

Five minutes later we had ascended to the aerial conning-tower, and all was in readiness to repeat the trial of the night before. Vicious and sly the Z99 looked in the daytime as she slipped off, under the unseen guidance of the wireless, with death hidden under her nose. Just as during the first trial we had witnessed, she began by fulfilling the highest expectations. Straight as an arrow she shot out of the harbour's mouth, half submerged, with her periscope sticking up and bearing the flag proudly flapping, leaving behind a wake of white foam.

She turned and re-entered the harbour, obeying Captain Shirley's every whim, twisting in and out of the shipping much to the amazement of the old salts, who had never become used to the weird sight. She cut a figure eight, stopped, started again.

Suddenly I could see by the look on Captain Shirley's face that something was wrong. Before either of us could speak, there was a spurt of water out in the harbour, a cloud of spray, and the Z99 sank in a ma.s.s of bubbles. She had heeled over and was resting on the mud and ooze of the harbour bottom. The water had closed over her, and she was gone.

Instantly all the terrible details of the sinking of the Lutin and other submarines flashed over me. I fancied I could see on the Z99 the overturned acc.u.mulators. I imagined the stifling fumes, the struggle for breath in the suddenly darkened hull. Almost as if it had happened half an hour ago, I saw it.

"Thank G.o.d for telautomatics," I murmured, as the thought swept over me of what we had escaped. "No one was aboard her, at least."

Chlorine was escaping rapidly from the overturned storage batteries, for a grave danger lurks in the presence of sea water, in a submarine, in combination with any of the sulphuric acid. Salt water and sulphuric acid produce chlorine gas, and a pint of it inside a good-sized submarine would be sufficient to render unconscious the crew of a boat.

I began to realise the risks we had run, which my confidence in Captain Shirley had minimised. I wondered whether hydrogen in dangerous quant.i.ties might not be given off, and with the short-circuiting of the batteries perhaps explode. Nothing more happened, however. All kinds of theories suggested themselves. Perhaps in some way the gasoline motor had been started while the boat was depressed, the "gas" had escaped, combined with air, and a spark had caused an explosion. There were so many possibilities that it staggered me. Captain Shirley sat stunned.

Yet here was the one great question, Whence had come the impulse that had sent the famous Z99 to her fate?

"Could it have been through something internal?" I asked. "Could a current from one of the batteries have influenced the receiving apparatus?"

"No," replied the captain mechanically. "I have a secret method of protecting my receiving instruments from such impulses within the hull."

Kennedy was sitting silently in the corner, oblivious to us up to this point.

"But not to impulses from outside the hull," he broke in.

Un.o.bserved, he had been bending over one of the little instruments which had kept us up all night and bad cost a tedious trip to New York and back.

"What's that?" I asked.

"This? This is a little instrument known as the audion, a wireless electric-wave detector."

"Outside the hull?" repeated Shirley, still dazed.

"Yes," cried Kennedy excitedly. "I got my first clue from that flickering Welsbach mantle last night. Of course it flickered from the wireless we were using, but it kept on. You know in the gas-mantle there is matter in a most mobile and tenuous state, very sensitive to heat and sound vibrations.

"Now, the audion, as you see, consists of two platinum wings, parallel to the plane of a bowed filament of an incandescent light in a vacuum.

It was invented by Dr. Lee DeForest to detect wireless. When the light is turned on and the little tantalum filament glows, it is ready for business.

"It can be used for all systems of wireless--singing spark, quenched spark, arc sets, telephone sets; in fact, it will detect a wireless wave from whatever source it is sent. It is so susceptible that a man with one attached to an ordinary steel-rod umbrella on a rainy night can pick up wireless messages that are being transmitted within some hundreds of miles radius."

The audion buzzed.

"There--see? Our wireless is not working. But with the audion you can see that some wireless is, and a fairly near and powerful source it is, too."

Kennedy was absorbed in watching the audion.

Suddenly he turned and faced us. He had evidently reached a conclusion.

"Captain," he cried, "can you send a wireless message? Yes? Well, this is to Burke. He is over there back of the hotel on the hill with some of his men. He has one there who understands wireless, and to whom I have given another audion. Quick, before this other wireless cuts in on us again. I want others to get the message as well as Burke. Send this: 'Have your men watch the railroad station and every road to it.

Surround the Stamford cottage. There is some wireless interference from that direction.'"

As Shirley, with a half-insane light in his eyes, flashed the message mechanically through s.p.a.ce, Craig rose and signalled to the house.

Under the portecochere I saw a waiting automobile, which an instant later tore up the broken-stone path and whirled around almost on two wheels near the edge of the cliff. Glowing with health and excitement, Gladys Shirley was at the wheel herself. In spite of the tenseness of the situation, I could not help stopping to admire the change in the graceful, girlish figure of the night before, which was now all lithe energy and alertness in her eager devotion to carrying out the minutest detail of Kennedy's plan to aid her father.

"Excellent, Miss Shirley," exclaimed Kennedy, "but when I asked Burke to have you keep a car in readiness, I had no idea you would drive it yourself."

"I like it," she remonstrated, as he offered to take the wheel.

"Please--please--let me drive. I shall go crazy if I'm not doing something. I saw the Z99 go down. What was it? Who--"

"Captain," called Craig. "Quick--into the car. We must hurry. To the Stamford house, Miss Shirley. No one can get away from it before we arrive. It is surrounded."

Everything was quiet, apparently, about the house as our wild ride around the edge of the harbour ended under the deft guidance of Gladys Shirley. Here and there, behind a hedge or tree, I could see a lurking secret-service man. Burke joined us from behind a barn next door.

"Not a soul has gone in or out," he whispered. "There does not seem to be a sign of life there."

Craig and Burke had by this time reached the broad veranda. They did not wait to ring the bell, but carried the door down literally off its hinges. We followed closely.