While the others speculated upon various means of escape, and in turn found every one of their suggestions useless, Lieutenant Mackinson had remained silent and in deep thought. Finally, his countenance showing that he had arrived at a conclusion, he turned to the others.

"Come with me," he said simply, "it is the only way."

"Where are you going?" Joe asked quickly.

"Back to the tractor," the lieutenant replied. "Hurry! We still have time, but none to waste."

"But we can't repair the tractor," Frank argued.

"No, we can't," Lieutenant Mackinson admitted, "but we may do something even better than that."

"What?" queried all the lads at once.

"Come with me and we'll see what can be done."

And without granting them any further information then, Lieutenant Mackinson swung his share of the burdens to his shoulder and started down the rough mountain road, the others following, and likewise bearing the various necessities which, only a short time before, they had labored so industriously to carry up the mountain.

As they neared the point where they had left the wrecked machine the young officer turned to Joe, who was nearest to him.

"Do you remember," he asked, "seeing that wire of the old telegraph line just about a hundred yards below where we ran the truck into the wall?"

"I saw it," Joe admitted, "but I didn't pay any further attention to it."

The others had come up within hearing distance.

"Well," the lieutenant responded, "if you had traced its course you would have seen that it is swung from this mountain to the one directly to the south, just at the point where the valley between narrows down to little more than a deep ravine."

"But it doesn't run into our lines," Frank objected again.

"That's true," Lieutenant Mackinson admitted again, "but it may serve our purposes just the same."

"How?" Slim asked entreatingly. "Tell us what your plan is, Lieutenant."

"No," replied the young officer in teasing tones, "I don't want to raise your hopes until I determine whether it can be accomplished."

And he plodded on toward the tractor, refusing to answer another question. Indeed, it is doubtful if he heard them, for he was busy with some important mental calculations—problems that required his engineering knowledge and ability, and that had directly to do with the personal safety of every man in the party.

"What tools have we here?" he asked of Frank Hoskins, as they arrived at the wrecked wireless tractor.

Frank opened up a tool chest that showed a great variety of implements in almost every size and shape.

"Good," said the lieutenant, as he looked up from where he was rummaging in another part of the car. "Here, Jerry," he commanded, "let me have that mallet and cold chisel and then help me rip a couple of these boards off the floor."

He had laid aside a large pulley wheel, several nuts and bolts and some heavy copper wire. With the aid of the mystified Jerry he tore two stout boards up from the floor of the tractor.

"Now we've got to work rapidly, fellows," he said, "for it will soon be dark, and we don't want to attract attention to ourselves by making a light.

"Here is what I am going to try to do: That wire is strung really from mountain to mountain, running down a slight grade from where it is fastened here to where it is tied up over there. I don't know how strong it is, or how securely it is fastened at the other end, but I'm going to find out.

"You've all seen those trolley-like boxes that run on wires in department stores, with which the clerk sends your money to the cashier's desk, and the cashier returns the change? Well, I'm going to construct something on the same principle, only I want to make it strong enough to carry my weight.

"If I can do that, and the wire holds, the incline is sufficient to carry a passenger to the other mountain without any propelling power. I'll try it first, and carry with me one end of this reel of copper wire. If I get over all right I'll attach the wire to the little oar and you fellows can haul it back for the next passenger, and so on until all of us are over."

Slim looked dubious. "How thick is that wire?" he demanded anxiously.

"You know Slim's a trifle heavy," Jerry reminded the lieutenant.

"Well," said Slim in a serious tone, "I'd rather fall into the hands of the Germans, and have some chance for my life, than spatter myself all over the bottom of that ravine."

While this conversation was going on, Lieutenant Mackinson was boring a hole about two inches in from each of the four comers of one of the planks taken from the floor of the truck.

"This ought to do for a seat," he said, as he began running pieces of the heavy copper wire, of equal length, through each of the holes.

He then laid this part of the work aside for a moment and began filing off one end of the riveted axle that held the pulley wheel in its frame. When he had knocked this axle out he tried one of the bolts and found that it fitted almost exactly, and that the wheel ran freely upon it.

"Have to have that wheel off to put the thing on the telegraph wire," he explained, as he began securely fastening the copper wires into the bottom of the pulley frame.

Completed, the thing looked for all the world like a miniature trapeze seat.

"Now," he said, slipping a wrench into his pocket, and buckling on his legs a pair of spurs such as all linemen use to climb a smooth pole, "I'm going to take this up that telegraph pole with me and fasten this thing on the wire. Then it's 'All aboard for the opposite mountain.'

"If I get over all right I'll give one flash of my light. If I don't—well, don't try the wire route."

Without wasting another second he dug one spur into the pole and started climbing upward, dragging his improvised car with him, together with the loose end of the reel of copper wire.

By this time it was pitch dark, and they could feel, rather than see, that he was tightening the bolt which hung the apparatus on the wire. The lads had placed a heavy stick through the reel, and two of them held either end of it.

"Let it run free," the lieutenant told them. "And don't forget the signal. I'm ready. Good-by!"

There was a sudden jerk on the reel and the wire began to unwind quickly. It literally spun round on the stout stick which they were holding. They just got a glimpse of the courageous lieutenant sailing off through space, a thousand feet above the bottom of the ravine.

The unwinding wire gave an added spurt, and then, pressure being released from it, it began to slow down.

"He's either on the other side, or lost the wire," said Slim, his nervousness showing in his voice.

Every eye was glued to the opposite mountain.

"Look!" almost shouted Jerry. "He's safe!"

Sure enough, the light had flashed out once in the blackness of the night, and then as suddenly disappeared.

The boys began hauling in on the copper wire, winding it again on the reel.

"Who's next?" asked Frank, as the last of the cable was being re-wound.

"Eenie, meenie, minie, mo," Jerry began to count out, when Joe suddenly interrupted.

By ten feet of heavy twine Lieutenant Mackinson had tied the spurs to the car so that they would dangle within reach of the lads on the ground. Attached to them was a note, which read:

And so Slim, not entirely assured, and breathing somewhat heavily as he contemplated the distance he had to fall if the telegraph wire should break, was the next to climb a-straddle the crude "air-line" trolley, on its second trip to the opposite mountain.

In a few moments the light flashed out again and then disappeared, while Joe, Jerry and Frank hauled in on the cable to which the car was attached.

By mutual agreement it was arranged that Frank should be the next to go over, after which they would send the portable wireless, followed by Jerry, and finally Joe.

Lads of less courage never would have attempted such a perilous escape, but they made it without a single mishap. It was not until Joe, the last of the party, was just coming to a stop in the outstretched arms of his friends, that the Germans below, and on what was now the opposite mountain, seemed to sense something going on—or perhaps had seen the mysterious blinking of the flashlight—and let go a distant and futile volley of shots.

"No use, Boche," called the lieutenant mockingly, "we're out of your range. And now, having escaped you, we'll see what we can do to harass you."

Saying which he began opening up the pack-set wireless, while two of the others set up the umbrella antenna.

Lieutenant Mackinson began tapping off the headquarters call. It might have been the slightly nearer position they were in, or, so far as they knew, headquarters might have moved meanwhile, but in a very short time the operator there was responding.

The young officer gave an accurate account of the operations of the Germans, and particularly of their artillery. Headquarters thanked them, told them to stay until morning where they were, and then ask for further orders.

In less than half an hour the boom of heavy guns from the westward told them that they had given their information in time.

American artillery was dropping a rain of shells into the cuts in the mountain through which the Germans had to emerge with their guns to do any damage! Their whole plan, so carefully carried out, had been defeated!