"From what I was able to observe during the equinoctial tides, I should think that we are in the axis of the tunnel."

"All right," he replied.

Yes, it was all right, and I felt that Providence was speaking by the mouth of the officer. Certainly Providence could not have chosen a better agent to work its will.

In the light of the lamp I examined him. He was about thirty years of age, cool, phlegmatic, with resolute physiognomy--the English officer in all his native impassibility--no more disturbed than if he had been on board the _Standard_, operating with extraordinary _sang-froid,_ I might even say, with the precision of a machine.

"On coming through the tunnel I estimated its length at about fifty yards," he remarked.

"Yes, Lieutenant, about fifty yards from one extremity to the other."

This calculation must have been pretty exact, since the new tunnel cut on a level with the coast is thirty-five feet in length.

The order was given to go ahead, and the _Sword_ moved forward very slowly for fear of colliding against the rocky side.

Sometimes we came near enough to it to distinguish a black mass ahead of it, but a turn of the wheel put us in the right direction again. Navigating a submarine boat in the open sea is difficult enough. How much more so in the confines of a lagoon!

After five minutes' manoeuvring, the _Sword_, which was kept at about a fathom below the surface, had not succeeded in sighting the orifice.

"Perhaps it would be better to return to the surface, Lieutenant," I said. "We should then be able to see where we are."

"I think you are right, Mr. Hart, if you can point out just about where the tunnel is located."

"I think I can."

"Very well, then."

As a precaution the light was turned off. The engineer set the pumps in motion, and, lightened of its water ballast, the boat slowly rose in the darkness to the surface.

I remained at my post so that I could peer through the lookouts.

At last the ascensional movement of the _Sword_ stopped, and the periscope emerged about a foot.

On one side of me, lighted by the lamp by the shore, I could see the Beehive.

"What is your opinion?" demanded the lieutenant.

"We are too far north. The orifice is in the west side of the cavern."

"Is anybody about?"

"Not a soul."

"Capital, Mr. Hart. Then we will keep on a level with the surface, and when we are in front of the tunnel, and you give the signal, we will sink."

It was the best thing to be done. We moved off again and the pilot kept her head towards the tunnel.

When we were about twelve yards off I gave the signal to stop. As soon as the current was turned off the _Sword_ stopped, opened her water tanks and slowly sank again.

Then the light in the lookout was turned on again, and there in front of us was a black circle that did not reflect the lamp's rays.

"There it is, there is the tunnel!" I cried.

Was it not the door by which I was going to escape from my prison? Was not liberty awaiting me on the other side?

Gently the _Sword_ moved towards the orifice.

Oh! the horrible mischance! How have I survived it? How is it that my heart is not broken?

A dim light appeared in the depth of the tunnel, about twenty-five yards in front of us. The advancing light could be none other than that, projected through the lookout of Ker Karraje's submarine boat.

"The tug! The tug!" I exclaimed. "Lieutenant, here is the tug returning to Back Cup!"

"Full speed astern," ordered the officer, and the _Sword_ drew back just as she was about to enter the tunnel.

One chance remained. The lieutenant had swiftly turned off the light, and it was just possible that we had not been seen by the people in the tug. Perhaps, in the dark waters of the lagoon, we should escape notice, and when the oncoming boat had risen and moored to the jetty, we should be able to slip out unperceived.

We had backed close in to the south side and the _Sword_ was about to stop, but alas, for our hopes! Captain Spade had seen that another submarine boat was about to issue through the tunnel, and he was making preparations to chase us.