With parts from the wrecked electric airship the youth rigged up a plant, and sent wireless messages from the island. The castaways nearly lost their lives in the earthquake shocks, but a steamer, summoned by Tom's wireless call, arrived in time to save them, just as the island disappeared beneath the sea.

In the seventh book of the series, ent.i.tled "Tom Swift Among the Diamond Makers" there was related the adventures of himself and his friends when they tried to solve the mystery of Phantom Mountain.

Among the castaways of Earthquake Island was a Mr. Barcoe Jenks and a Professor Ralph Parker. Mr. Jenks was a strange man, and claimed to have some valuable diamonds, which he said were made by a gang of men hidden in a cave in the Rocky Mountains. Tom did not believe that the diamonds were real, but Mr. Jenks soon proved that they were.

He asked Tom to aid him in searching for the cave of the diamond makers. Mr. Jenks had been there once--in fact, he had been offered a partnership in the diamond-making business, but, after he had paid his money, he had been drugged, and carried secretly from the cave before he had a chance to note its location.

But he, together with Tom, Mr. Damon and the scientist Mr. Parker, who correctly predicted the destruction of Earthquake Island, set out in the RED CLOUD to find the diamond makers. They did find them, after many hardships, and were captured by the gang. How Tom and his friends escaped from the cave, after they had seen diamonds made by a powerful lightning flash, and how they nearly lost their lives from the destruction of Phantom Mountain, is fully set down in the book.

Sufficient to say now, that, though they had a general idea of how the precious stones were made, by the power of the lightning, the young inventor and his friends were never quite able to accomplish it, and the secret remained a secret. But they had secured some diamonds as they rushed from the cave (Mr. Damon grabbing them up) and these were divided among Tom and the others.

Just as they were ready to come home in the airship, our friends were met by an old miner, Abe Abercrombie, who spoke of a valley of gold in Alaska, which was the story Tom related to Ned Newton, as the two chums sat in the den of the airship shed.

"Then you don't know all the details about the gold valley, Tom?"

remarked Ned, as the young inventor showed his chum the letter that had just arrived.

"No, not all of them. At the time this miner met us I was anxious to get back East, for we had been away so long I knew dad would be worried. But I listened to part of Abe's story, and half promised to go in partnership in this quest for gold. He was to furnish information about the hidden valley, and I was to supply the airship. I expect Abe to come along at any time, now, and then I'll hear more particulars."

"Will you go all the way in the airship?"

"Well, I hadn't thought of that. I could ship it to the nearest place by rail, I suppose, and go on from there. That's a detail to be considered later. I'll talk it over with Abe."

"Who are going?"

"I don't know that even. I suppose Mr. Damon would feel slighted if I left him out. And perhaps Mr. Parker, that gloomy scientist, who is always predicting terrible accidents, will be glad to go along.

Then Abe may have some friend he wants to take."

"By Jinks! But you certainly do have swell times, Tom Swift!"

exclaimed Ned Newton, enviously. "I wish I could go and have a try at that valley of gold!"

"Why don't you come along, Ned?"

"Do you really mean it?"

"Of course."

"But I don't believe I could get away from the bank."

"Oh, dad and Mr. Damon could fix that. They're directors, you know.

Come along, I'd be delighted to have you. Will you?"

"I'll think about it. Jinks! But I sure would like to go. Do you think you can find the valley?"

"Well, there's no telling. We generally do succeed in finding what we go after, even if we didn't get the diamond secret. I'm anxious to have Abe come, now, though until I got his letter I had almost forgotten about my promise to him. But, say, what's this you told me about Andy Foger making an airship?"

"It's true, though I haven't seen it. Jake Porter was telling me about it. Andy's built a big shed in his yard, and he and some cronies of his, including Pete Bailey and Sam Snedecker, are working in there night and day. They've hired a couple of machinists, too.

Mr. Foger is putting up the cash, I guess. Say, that was quite a scare you gave Andy on your monoplane, one day."

"Yes, the big bully! and I'd like to scare him worse. But say, do you know I'd like to get a look at his airship. I wonder what sort of a craft it is?"

"We can see it easily enough."

"How?"

"Why, the back part of the shed where he and the others are working is close to our fence. There are some holes in our fence and if you come there, maybe you can look in."

"I can't see through the side of the shed, though."

"Yes, you can."

"How?"

"Why, there's a big window, for light, in the back part of it. I happened to notice it the other day. I didn't look in, because I wasn't much interested, but I saw that one could peer over the top of our fence right into the shop where Andy is working. Want to try it?"

Tom hesitated a moment.

"Well, it seems rather an odd thing to do," he said. "But I would like to see what sort of a flying machine Andy is making, just for my own satisfaction. He may be infringing on some of my patents, and if he is, I'll stop him. Once or twice he's been sneaking around my shed here. I don't believe in sneaking, but I know he wouldn't let me in if I asked him, so I guess it's the only way. I'll go with you, Ned."

"All right. We'll see if we can get a glimpse of Andy's queer shebang through the window."

The two chums left Tom's shop, and were soon in the yard of Ned Newton's house. As he had said, the big shed in Andy's premises came close up to the fence, and there was a window through which one might gaze. The cas.e.m.e.nt did not appear to be curtained.

"I'll get a ladder so we can climb up to the top of the fence, and look over," spoke Ned, as he and Tom went out into the yard back of his house. The fence was high up on an embankment.

A little later Tom and his chum were gazing into the shop window from the ladder.

"Why, it's a triplane--a big triplane!" he exclaimed.

"What's a triplane?" asked Ned, who didn't have much time to study the different types of airships.

"It's one that has three sets of planes, one above the other. A biplane has two sets of planes, and a monoplane only one. Triplanes are larger, and, as far as I've been able to learn, not as satisfactory as either the biplanes or monoplanes. But that's not saying Andy's won't be a success. They certainly are busy in there, though! Andy is flying around like a hen scratching for her little chickens!"

"See anything of his cronies?"

"Yes, Pete and Sam are hammering away. There are a couple of men, too."

"Yes, the machinists. Oh, I guess Andy expects great things from his airship."

"Have you heard what he's going to do with it, Ned? Make flights for pleasure, or exhibit it?"

"No, I haven't heard. Look out, Tom, the ladder is slipping!"

As Ned spoke this warning, the window of the airship shed, through which they were looking, was suddenly raised. The ugly face of Andy Foger peered out. He caught sight of Tom and Ned.

"Get away from there, you spies!" he yelled. "Get away from there, Tom Swift! You're trying to steal some of my ideas! Get away or I'll make you. Sam, bring me my gun! Pete, go tell my father to come here! I'll show Ned Newton and Tom Swift they can't bother me!"

Andy was dancing about in a rage. His two cronies crowded behind him to the window just as the ladder on which Tom and Ned were standing slipped along the fence.