He was speedily furnished with a peaked yachting cap belonging to Nat. It sat oddly, almost comically, on his large head, but none of the boys was inclined to laugh at the professor just then. They were far too interested in hearing what the eccentric man had to tell about the voyage of the Tropic Bird.

“We sailed from San Francisco, as you no doubt know from the papers,” said the professor, “without the object of our mission being divulged. There is no harm in telling it now.

“It had been ascertained that a certain phase of the sun spots would be reached on this present day. As you are perhaps aware, it has long been a theory of scientific men that there was some intimate relation between that phenomenon and the volcanic disturbances and earthquakes that occur in these seas from time to time.”

“I think that we learned something like that in physics,” said Nat, nodding.

“In physic?” chuckled Joe, but was frowned down.

The professor went on:

“It was my duty, assigned to me by the Smithsonian Institute and the British Royal Geographical Society, working in concert, to investigate such a disturbance and make elaborate reports thereon. At my suggestion, it was also decided to engage a moving-picture operator to take photos of the whole scene, which must prove of inestimable benefit to scientific knowledge. The Tropic Bird was chartered to convey the expedition, and Mr. Tubbs was placed under contract to take the pictorial record of the scene, if we were fortunate enough to encounter one.

“We cruised about for some time, awaiting the exact condition of the sun spots which would indicate that a phenomenon of the kind I was in search of was about to be demonstrated. Some days ago my observations showed me that the desired condition was at hand. As fortune would have it, on that very day we sighted these islands—or rather those islands, for they have completely vanished as I predicted they would.

“We landed, and found the islands to be of distinctly volcanic origin, and, seemingly, of recent formation. At any rate, they are not charted.”

Nat nodded.

“Of course there was no trace of habitation. But a few creepers and shrubs of rapid growth had taken root in the clefts of the lava-like rock, of which the islands were composed. I saw at once that it was here, if anywhere, that a seismic disturbance would result, in all probability, providing the conditions were favorable. That night, on our return to the ship, the captain of it waited on me.

“After much beating about the bush, he informed me that his crew was aware of my belief that the islands would be the center of a volcanic disturbance, and that they refused to remain in the vicinity. He denied being alarmed himself, however. I succeeded in calming the crew’s fears, and we remained at anchor off the islands for some days. At last, signs of the storm which broke to-day began to make themselves manifest on my instruments. I realized that the great moment was at hand.

“I warned Mr. Tubbs, here—a most valuable assistant—to be ready at any moment. I was confident that with the breaking of the storm the islands would vanish. But nothing was said to the crew. Quite early to-day Mr. Tubbs and I embarked in that small boat and lay off the islands. I was certain that the storm would be magnetic in character, and would break with great fury.”

“However did your boat live through it?” asked Nat.

“She is fitted with air chambers, and specially built to weather any storm,” was the reply. “But to resume: The cowardly captain, when he saw the storm coming up, sounded a signal for us to return on board. When we did not, he hoisted sail and made off, leaving us to our fate. The storm broke, and there was a spectacle of appalling magnificence. Mr. Tubbs behaved with the greatest heroism throughout.”

Here Mr. Tubbs blushed as red as his own hair, and waved a deprecatory hand.

“I guess it was watching you kept me from feeling scared,” he declared, addressing the professor; “but anyhow, I got my pictures.”

“We have some faint idea of what the storm was,” put in Nat; “but can you explain something to us?” and he described to the professor the manner in which the Nomad had been drawn toward the volcanic islands.

“Pure magnetism,” declared the scientist, “a common feature of such storms.”

“But our craft is of wood,” declared Nat.

“Yes, but your engines, being metallic, of course, overcame that resistance. You are fortunate, indeed, not to have been drawn down when the islands vanished. It was a terrific sight.”

Nat explained that during that period they were all unconscious and then went on to tell of the experiences through which they had passed.

“Oh, why wasn’t I on board your craft?” moaned Mr. Tubbs, as he concluded. “What a picture that chasm would have made! It’s the opportunity of a lifetime gone.”

The boys could hardly keep from smiling over his enthusiasm; but Nat struck in with:

“It’s an opportunity I don’t want to encounter again,” an opinion with which everybody but Mr. Tubbs—even the professor—concurred.

“And now,” said the man of science suddenly, “I don’t wish to alarm you, young men, but it is possible that there may be some reflex action exerted by this storm. In other words, there may be a mild recurrence of it. In my opinion we had better get as far away from this spot as possible.”

The others agreed with him. Ding-dong dived below to his engines. Nat took his station on the bridge.

“By the way, what about the boat?” asked Nat suddenly, referring to the craft from which they had rescued the scientist and his assistant.

“Unless you want it, we will let it drift,” said the professor. “It is too large for you to hoist conveniently, and it would impede your speed if you towed it.”

And so it was arranged to leave the boat behind, but Mr. Tubbs took a series of pictures of it as the Nomad sped away. The professor also waved the craft, in which they had weathered so much, a farewell. But, when doing so, in some manner the peak of his borrowed cap slipped from between his fingers. The headpiece went whirling overboard, and fell into the sea with a splash.

“God bless my soul, I’ve lost my hat!” he exclaimed for the second time that day, as the catastrophe happened.

“He’ll use up every hat on board. You see if he don’t,” confided Mr. Tubbs to Nat, while the professor gazed fondly at the spot where the cap had vanished.