Tom Swift's electric runabout, which he built after returning home from the submarine trip, proved to be the speediest car on the road. The experience he acquired in making this machine stood him in good stead, when (as told in the sixth volume, "Tom Swift and His Wireless Message") the airship in which he, Mr. Damon and a friend of the latter's (who had built the craft) were wrecked on Earthquake Island. There Tom was marooned with some refugees from a wrecked steam yacht, among whom were Mr. and Mrs. Nestor, father of a girl of whom Tom thought a great deal.
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, entitled "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."