The men stopped work immediately and hid in the brush. Our car pa.s.sed over the bridge and we saw nothing wrong. But no sooner had we gone than the men crept out and resumed work which had progressed to the point where they were ready to carry the wires of an electric connection through the gra.s.s, concealing them as they went.

In the study of his bungalow, all this time, Del Mar was striding angrily up and down, while his men waited in silence.

Finally he paused and turned to one of them. "See that the coast is clear and kept clear," he ordered. "I want to go down."

The man saluted and went out through the panel. A moment later Del Mar gave some orders to the other man who also saluted and left the house by the front door, just as our car pulled up.

Del Mar, the moment the man was gone, put on his hat and moved toward the panel in the wall. He was about to enter when he heard some one coming down the hall to the study and stepped back, closing the panel.

It was the butler announcing us.

We had entered Del Mar's bungalow and now were conducted to his library. There Elaine told him the whole story, much to his apparent surprise, for Del Mar was a wonderful actor.

"You see," he said as she finished telling of the finding and the losing of the torpedo, "just what I had feared would happen has happened. Doubtless the foreign agents have the deadly weapon, now.

However, I'll not quit. Perhaps we may run them down yet."

He rea.s.sured us and we thanked him as we said good-bye. Outside, Elaine and I got into the car again and a moment later spun off, making a little detour first through the country before hitting the sh.o.r.e road back again to Dodge Hall.

On the rocky sh.o.r.e of the promontory, several men were engaged in sinking a peculiar heavy disk which they submerged about ten or twelve feet. It seemed to be held by a cable and to it wires were attached, apparently so that when a key was pressed a circuit was closed.

It was an "oscillator", a new system for the employment of sound for submarine signalling, using water instead of air as a medium to transmit sound waves. It was composed of a ring magnet, a copper tube lying in an air-gap in a magnetic field and a stationary central armature. The tube was attached to a steel diaphragm. Really it was a submarine bell which could be used for telegraphing or telephoning both ways through water.

The men finished executing the directions of Del Mar and left, carefully concealing the land connections and key of the bell, while we were still at Del Mar's.

We had no sooner left, however, than one of the men who had been engaged in installing the submarine bell entered the library.

"Well?" demanded Del Mar.

"The bell is installed, sir," he said. "It will be working soon."

"Good," nodded Del Mar.

He went to a drawer and from it took a peculiar looking helmet to which was attached a sort of harness fitting over the shoulders and carrying a tank of oxygen. The head-piece was a most weird contrivance, with what looked like a huge gla.s.s eye in front. It was in reality a submarine life-saving apparatus.

Del Mar put it on, all except the helmet which he carried with him, and then, with his a.s.sistant, went out through the panel in the wall.

Through the underground pa.s.sage the two groped their way, lighted by an electric torch, until at last they came to the entrance hidden in the underbrush, near the sh.o.r.e.

Del Mar went over to the concealed station from which the submarine bell was sounded and pressed the key as a signal. Then he adjusted the submarine helmet to his head and deliberately waded out into the water, further and further, up to his head, then deeper still.

As he disappeared into the water, his emissary turned and went back toward the sh.o.r.e road.

The ride around through the country and back to the sh.o.r.e, road from Del Mar's was pleasant. In fact it was always pleasant to be with Elaine, especially in a car.

We were spinning along at a fast clip when we came to a rocky part of the coast. As we made a turn a sharp breeze took off my hat and whirled it far off the road and among the rocks of the sh.o.r.e. Elaine shut down the engine, with a laugh at me, and we left the car by the road while we climbed down the rocks after the hat.

It had been carried into the water, close to sh.o.r.e and, still laughing, we clambered over the rocks. Elaine insisted on getting it herself and in fact did get it. She was just about to hand it to me, when something bobbed up in the water just in front of us. She reached for it and fished it out. It was a cylinder with air-tight caps on both ends, in one of which was a hook.

"What do you suppose it is?" she asked, looking it over as we made our way up the rocks again to the car. "Where did it come from?"

We did not see a man standing by our car, but he saw us. It was Del Mar's man who had paused on his way to watch us. As we approached he hid on the other side of the road.

By this time we had reached the car and opened the cylinder. Inside was a note which read:

"Chief arrived safely. Keep watch."

"What does it mean?" repeated Elaine, mystified.

Neither of us could guess and I doubt whether we would have understood any better if we had seen a sinister face peering at us from behind a rock near-by, although doubtless the man knew what was in the tube and what it meant.

We climbed into the car and started again. As we disappeared, the man came from behind the rocks and ran quickly up to the top of the hill.

There, from the bushes, he pulled out a peculiar instrument composed of a strange series of lenses and mirrors set up on a tripod.

Eagerly he placed the tripod, adjusting the lenses and mirrors in the sunlight. Then he began working them, and it was apparent that he was flashing light beams, using a Morse code. It was a heliograph.

Down the sh.o.r.e on the top of the next hill sat the man who had already given the signal with the handkerchief to those in the valley who were working on the mining of the bridge. As he sat there, his eye caught the flash of the heliograph signal. He sprang up and watched intently.

Rapidly he jotted down the message that was being flashed in the sunlight:

Dodge girl has message from below.

Coming in car. Blow first bridge she crosses.

Down the valley the lookout made his way as fast as he could. As he approached the two men who had been mining the bridge, he whistled sharply. They answered and hurried to meet him.

"Just got a heliograph," he panted. "The Dodge girl must have picked up one of the messages that came from below. She's coming over the hill now in a car. We've got to blow up the bridge as she crosses."

The men were hurrying now toward the bridge which they had mined. Not a moment was to be lost, for already they could see us coming over the crest of the hill.

In a few seconds they reached the hidden plunger firing-box which had been arranged to explode the charge under the bridge. There they crouched in the brush ready to press the plunger the moment our car touched the planking.

One of the men crept out a little nearer the road. "They're coming!" he called back, dropping down again. "Get ready!"

Del Mar's emissaries had not reckoned, however, that any one else might be about to whom the heliograph was an open book.

But, further over on the hill, hiding among the trees, the old farmer and his dog were sitting quietly. The old man was sweeping the Sound with his gla.s.ses, as if he expected to see something any moment.

To his surprise, however, he caught a flash of the heliograph from the land. Quickly he turned and jotted down the signals. As he did so, he seemed greatly excited, for the message read:

Dodge girl has message from below.

Coming in car. Blow first bridge she crosses.

Quickly he turned his gla.s.ses down the road. There he could see our car rapidly approaching. He put up his gla.s.ses and hurried down the hill toward the bridge. Then he broke into a run, the dog scouting ahead.

We were going along the road nicely now, coasting down the hill. As we approached the bridge, Elaine slowed up a bit, to cross, for the planking was loose.

Just then the farmer who had been running down the hill saw us.

"Stop!" he shouted.