Nat sat upright with a strange singing sound in his ears. It was insufferably hot. He fairly panted as he opened his eyes. The sweat ran off him in rivulets. For an instant recollection paused, and then rushed back in an overwhelming flood.

“We were in that channel between those two queer islands,” mused Nat; “and we—gracious, where are the islands?”

He had staggered dizzily to his feet and was looking about him. He knew he could not have lain senseless very long, for his garments were still wet, despite the intense heat. But the islands were nowhere to be seen.

It was still partially dark, a murky twilight replacing the former deeper blackness. But an indefinable change had taken place, somehow, in the atmosphere. Nat drew in his breath with difficulty. It seemed to scorch his lungs.

He glanced over the side of the craft and then drew back with an alarmed cry. The water all about them was bubbling and eddying furiously. A shower of spray from one of the miniature waterspouts struck Nat in the face. It was this that caused his exclamation and made him step back hastily, just as if, in fact, he had been struck a blow in the face.

The water was boiling hot!

Where it had spattered on the lad’s skin it had instantly raised blisters.

“Well, we certainly have landed in a surprising sort of fix this time,” muttered Nat to himself.

He bent over Joe. The lad had not yet regained his senses. But he was breathing heavily, and this stilled a dreaded fear, which, for a moment had almost caused Nat’s heart to stop beating.

“This air is suffocating,” gasped Nat presently. “It smells like it does when they are fumigating a room.”

He ran his tongue around his dry mouth in an effort to moisten it, for it felt parched and cracked. The reek of sulphur in the air, too, caused his throat to contract and his nose and eyes to tingle unmercifully.

But this stench also told Nat something. It furnished him with a partial explanation of the extraordinary occurrences that, as it seemed, were not yet over.

“This whole disturbance is volcanic,” reasoned the boy. “That is the cause of this awful sulphur smell. But that doesn’t account altogether for the sudden disappearance of those islands. I wonder——” But here he broke off his meditations.

Joe was plainly in need of immediate attention, and Nat devoted his efforts to trying to raise the recumbent lad. He wanted to get him below to the cabin, where there was a well-stocked medicine chest and a supply of reasonably cool water.

But, weakened as he was, Nat couldn’t accomplish the task.

“What’s the matter with me, anyhow?” he asked himself half angrily. “This sulphur stuff must have knocked all my senses out of my head. Where’s Ding-dong, I wonder?”

He rang the engine-room call sharply. But there was no response. No Ding-dong appeared.

“Maybe the signal is out of whack,” muttered Nat, who had noticed some time before that the engine had stopped running. “Guess I’ll go below and see what’s the matter.”

It was the work of an instant to reach the hatchway leading below, and dive into the engine room. What met Nat’s eyes there made him jump almost as violently as he had when the boiling water struck him.

“Great Scott!” he exclaimed, as his gaze fell on the unconscious engineer, “if this isn’t worse and more of it. Poor Ding-dong is knocked out, too; cut on the head. It doesn’t seem to be a bad gash, but it has deprived him of his senses. Well, if this isn’t a fine kettle of fish! In the midst of a boiling sea with two unconscious chaps on my hands!”

Ding-dong stirred and moved uneasily as Nat examined his wound.

“Let me be!” he muttered peevishly; “lemme be.”

“That’s just what I’m not going to do,” rejoined Nat cheerfully.

On the wall of the engine room was a tap leading from the drinking water tanks of the craft. Nat saturated his handkerchief under this faucet and bathed Ding-dong’s wound. Then he applied the water plentifully to the lad’s face, and, opening his shirt, doused him with it.

Under this treatment, the unconscious lad sat up and opened his eyes.

“Hullo, Nat!” he exclaimed, like one awakening from a long sleep. “What’s up? What on earth has happened? Where are we? What makes it so hot?”

As usual, under strong excitement, Ding-dong forgot to stutter, as Joe termed it.

“I can only answer two of your questions,” replied Nat. “‘What’s up’ is that poor Joe is lying senseless on the bridge. He was washed overboard in that chasm. You’ve got to try to help me get him to the cabin. ‘What on earth has happened,’ is this: We have, apparently, passed through the chasm, and the islands have vanished in some mysterious fashion, although we can’t be far from where they were. The sea all about us is boiling hot, and I guess we are in the very core of some strange volcanic disturbance or other.”

“Cc-c-c-crickets!” sputtered Ding-dong, rising dizzily but pluckily to his feet, “we do seem to run into some mighty queer adventures, don’t we? Come on. I’ll give you a hand with poor old Joe. But, by the way, what have you been doing all this time?”

“Oh, I-I-guess I went to sleep for a while, too,” responded Nat, rather confusedly, and without mentioning his heroic rescue of Joe from the waters of the rift.

He was spared answering further questions, for it required their united strength to carry Joe to the cabin. Ordinarily, this would not have been so, but the heat was so terrific that it had sapped the strength of both boys till they had but half of their accustomed energy and vim.

Joe was laid on a locker and restoratives applied. Presently he was able to sit up, and then out came the story of Nat’s rescue. The lad colored brilliantly as Joe and Ding-dong both poured out their praise unstintedly.

“But, say,” exclaimed Joe, rubbing his head and looking suddenly bewildered, “I’ve got an awful bump here. I guess I must have hit my head before your brave——”

“I hit it for you to keep you quiet,” burst out Nat; “and if you don’t shut up now, I’ll bust it again.”

Going on deck, the three lads found that it had grown lighter. But the water still boiled about them furiously. Clouds of sulphurous steam arose from it, making them cough and choke.

In the brighter light they had quite an extensive view of their surroundings. But, of the islands, not a trace appeared. They had vanished as if they had been the fabric of a dream.

“By George! I have it!” cried Joe suddenly. “Those islands were of volcanic origin. Didn’t you notice how bare and bleak they were? I’ll bet that in this disturbance, whatever it is, they have subsided as suddenly as they arose.”

“Such cases are not uncommon,” rejoined Nat. “Only last year, Captain Rose, of the missionary schooner Galilee, of San Francisco, reported seeing an island of some extent arise and then vanish again before his very eyes.”

“W-w-w-well,” sputtered Ding-dong, with a grin and a return to his old manner, “w-w-w-we can r-r-r-report the same thing; but as t-t-this isn’t a go-go-gospel schooner maybe nobody w-w-w-will believe us.”

“My suggestion is, that we get the engines going and get out of this without delay,” said Nat.

“Here, too,” agreed Joe Hartley. “There’s nothing to hang about here for.”

An examination of the engines showed that, in falling, Ding-dong had shut off the gasolene supply valve, and had thus stopped the motors. This was soon remedied and the motors set going again. As the Nomad cut her way through the boiling sea where lately the twin islands had stood, they all felt like raising a fervent prayer of thanks to Providence for their wonderful deliverance.

“I’ve often heard of such things on the Pacific, but I never expected to live through one,” was Nat’s comment.

“Nor I,” was Joe’s rejoinder; “and I don’t know that I should care to repeat the experience. But hullo!” he broke off suddenly, “what’s that? No, not over there; off this way!”

He pointed excitedly to a small black object, which, in the now clear atmosphere, was visible at the distance of about a mile to the southeast of them.

“It’s a boat,” announced Nat, after a brief scrutiny of the strange object.