As they pa.s.sed up the ladder, I could no longer restrain myself.

"Craig," I cried, "this is devilish!"

I thought I saw it all now. In the cases of goods on the _Furious_ were some terrible infernal machines which had been hidden, to be detonated by these deadly rays of wireless.

Kennedy was busy, working quickly putting together the parts he had taken from the two packages we had carried.

As I watched him, I realized that the burning of the Rovigno house was not the action of an incendiary, after all. It had been done by these deadly rays, probably by mere accident.

As nearly as I could make it out, there was a counterplot against the _Furious_. Somewhere was an infernal workshop, possibly hedged about by doors of steel which ordinary force would find hard to penetrate, but from which, any moment, this super-criminal might send out his deadly power.

The more I considered it, while Kennedy worked, the more uncanny it seemed. This man had rendered the mere possession of explosives more dangerous to the possessor than to the enemy.

Archimedes had been outdone!

The problem before us now was not only the preservation of American neutrality, but the actual safety of life.

Through the open hatch I could now hear voices on the deck. One was that of a woman, which I recognized quickly. It was Julia Rovigno.

"I'll be just as quiet as a mouse," she was saying. "I'll stay in the cabin--I won't be in the way."

I could not hear the man's voice in reply, but it did not sound like Rovigno's. It was rather like Gaskell's.

Still, we had heard enough to know that Julia Rovigno was on the yacht, had insisted on going on the expedition for the excitement of the thing, just as we had heard over the detectaphone.

"Hadn't we better warn her?" I asked Craig, who had paused in his work at the sound of voices.

Before he could answer we were plunged in sudden darkness. Someone had switched out the light that had been shining down through the hatchway.

Before we knew it the opening to the hatchway had been closed.

CHAPTER XII

THE SUBMARINE BELL

Kennedy groped about for a light, stumbling over boxes and bags.

"For heaven's sake, Craig," I entreated. "Be careful. Those packages are full of the devilish things!"

He said nothing.

At least we had a little more freedom to move and I managed to find my way over to a little round porthole and open it.

As I looked out, I almost fainted at the realization. The _Furious_ was under way! We were locked in the hold--virtual prisoners--our only company those dastardly infernal machines, whose very nature we did not know!

Helplessly I gazed around me. There seemed to be only this one porthole, open, looking out over the dark and turbulent water, which slipped ominously past as we gained speed.

Why had Kennedy not foreseen this risk? I glanced at him. He had found an electric light, connected with the yacht's dynamo, and, before turning it on, closed and covered the port so that it threw no reflection out.

Far from being disconcerted, on the contrary, he seemed rather pleased than otherwise at the unexpected turn of events.

As I looked at our scant and cramped quarters I could see absolutely no way of getting word to anyone off the _Furious_ who might help us.

What he was working on I did not know, but if it was some sort of wireless, even if we were able to send a message, what hope was there that it would get past the delicate wireless detector which this criminal must have somewhere near for tapping messages that were being flashed through the air? Had we not heard him say that the signal was to be an S O S sent, as it were, from the fleet far out on the ocean?

I could well have believed that Kennedy could rig up some means of communication. But, if the possessor of this terrible infra-red ray, or wireless wave, secret should learn that we, too, knew it, the only result that he would accomplish would be to insure our destruction immediately.

It was a foggy night and a drizzle had set in. The _Furious_ could not under such circ.u.mstances make such good speed as she was accustomed to make. Fortunately, also, the waves were not running high.

Craig had taken a desperate chance. How would he meet it? I watched him at work, fascinated by our peril.

Finishing as quickly as he could, he put out our sole electric light, unscrewed the bulb and attached to the socket a wire which he had connected with the instrument over which he had spent so many precious moments.

Through the little porthole he cast a peculiar disk, heavy, such as I had seen him place so carefully aboard the _Uncas_.

It sank in the water with a splash and trailed along beside the yacht, held by a wire, submerged, perhaps, ten or twelve feet.

He made a final inspection of the thing as well as he could by the light of a match, then pressed a key which seemed to close a circuit.

I could feel a dull, metallic vibration, as it were.

"What are you doing?" I asked, looking curiously also at an arrangement, like a microphone, which he had placed over his ears.

"It works!" he cried excitedly.

"What works?" I reiterated.

"This Fessenden oscillator," he explained. "It's a system for the employment of sound for submarine signals. I don't know whether you realize it, but great advance has been made recently since it was suggested to use water instead of air as the medium for transmitting signals. I can't stop to explain this apparatus just now, but it is composed of a ring magnet, a copper tube which lies in an air gap of a magnetic field, and a stationary central armature. The magnetic field is much stronger than that in the ordinary dynamo.

"The copper tube, which has an alternating current induced in it, is attached to solid disks of steel which in turn are attached to a steel diaphragm an inch thick. In the _Uncas_ I had a chance to make that diaphragm practically a part of the side of the ship. Here I have had to hang it overboard, with a large water-tight diaphragm attached to the oscillator."

I listened eagerly, even if I were not an electrical engineer.

"The same oscillator," he went on, "is used for sending and receiving, for, like the ordinary electric motor it is also capable of acting as a generator, and a very efficient one, too. All I have to do is to throw a switch in one direction when I want to telegraph or telephone under water, and in the other direction when I want to listen in."

I could scarcely credit what I heard. Craig had circ.u.mvented even the spectacular wireless. He was actually talking through water. Craig had virtually endowed himself with a sixth sense!

I watched him spellbound. Would he succeed in whatever it was that he was planning? I waited anxiously.

"There's the answer!" he exclaimed in sudden exultation. "Burke is on the _Uncas_. He tells me that he went to see Mrs. Petzka and she is with him--insisted on going, when she heard that her husband had been engaged by the _Furious_."

He waited a moment.

"You see, Walter," he resumed, "what I am doing is to send out signals by which the _Uncas_ can locate and follow us. She is fast, but, thank heaven, this yacht has to go slow tonight. Sound travels in water at a velocity of about four thousand feet a second. For instance, I find that I get an echo in about one-twentieth of a second. That is the reflected sound wave from the bottom, and indicates that we are in water of about one hundred feet depth. Then I get another echo in something over two seconds. That is the waves reflected from the _Uncas_, which has been hovering about, waiting for something to happen. They can't be much more than a mile and a half away, now. I had expected to signal them from the sh.o.r.e, a dock or something of the sort, using this oscillator to get around that fellow's wireless. But we're much better off on the boat."

I looked at him in amazement. "Surrounded by all this junk that may blow us to kingdom come any second?" I demanded.