The boat darkened the entrance for a few moments, and then glided by; while the cavern kept closing like some monstrous eye whose lid was pressed up from below, opening again fairly widely, enough almost to suggest the possibility of their pa.s.sing under; but closing again as the tide rose and sank in slow, regular pulsations.

But as they watched they could make out that the soft wave rose higher and higher and sank perceptibly less, while the prisoners' eyesight became so preternaturally sharp that they could detect the gradual opening of the sea anemones, as they spread out their starry crowns of tentacles after the first kiss of the water had moistened them. The many limpets, too, which had been tight up against the smooth rock, like bosses or excrescences, were visibly raising their sh.e.l.ls and standing up, partly detached.

Then a new horror attracted the boys, and made them almost frantic for the moment; for, as they crouched there in the bottom of the boat, watching the slowly diminishing amount of light which came in through the archway, the water softly and quickly, welled up, nearly shut the entry, and a wave ran up the pa.s.sage and pa.s.sed under the boat, which was heaved up so high that the gunwale grated against the roof, and they had to bend themselves down to avoid being pressed against the rock.

Then, as they lay there, they heard the wave run on and on, whispering and waking up the echoes far inside, till the whole of the interior seemed to be alive with lapping, hissing sounds, which slowly died away as the boat sank to nearly its old level, and the light flashed in once more.

"That's a hint to do something," said Vince, as he rose up, finding that his head nearly touched the sh.e.l.l-encrusted roof.

"Yes; to force our way out," said Mike excitedly. "We must before it's too late."

"It is too late, as I told you before," said Vince sharply. "Look for yourself. Can't you see that the arch is too small for the sides of the boat to get through? and at any moment another of those waves may come in. It's all right, Ladle, if you'll only be firm."

"I'll be as firm as you are," said the boy angrily.

"Then help me push her along."

Mike pressed his hands against the roof, Vince did the same; and they both thrust hard, but in spite of all the boat did not stir.

"Why, you're pushing to send it in," said Mike.

"And you to drive it out! What nonsense! This place is sure to get bigger inside, where the water has washed it out. We must get right in, beyond where the water rises."

Mike shuddered; for the silence and darkness of the place would, he felt, be horrible, and all the time he knew that the water would be gradually chasing them, like some terribly fierce creature, bent on suffocating them in its awful embrace.

Vince's was the stronger will; and his companion yielded, changing his tactics, and forcing the boat along for some distance before there was any change in the roof, which crushed down upon them as low as ever, and Mike began once more to protest.

"It's of no use," he said: "we may as well be smothered where we can see as here, where it is so dark. Let's go back as far as we can."

"No; I'm sure this place will open out more if we go farther in."

At that moment there was a loud, plashing noise far inward, and this raised such loud reverberations that Mike was fain to confess that the roof must be far higher.

Vince took advantage of this to urge his companion on; and a minute later they could not touch the rock above them with their hands, while a little farther on it could not be reached with an oar.

"Yes, it's bigger," granted Mike; "but we shall be suffocated all the same. There can't be enough air to last us till the tide goes down."

"We shall see," said Vince; and then, quite cheerily: "I say, this is better than wading, the same as we did in the seal hole."

"Yes, but there are seals here. I heard them."

"Yes, so did I, but what of that? We mustn't interfere with them, and they won't with us. Besides, we're in a boat now, recollect."

Mike recollected it well enough, but it did not comfort him much; however, he kept his thoughts to himself, and proposed that they should keep as near the light as they could.

"Better keep where the roof's highest," suggested Vince. "We shall be able to breathe more freely then."

After that they were both very silent, for they suffered horribly from the dread that as soon as the entrance was entirely closed up by the tide, they would be rapidly exhausting all the pure breathable air shut-in; and so deeply did this impress them, that before long a peculiar sensation of compression at the chest a.s.sailed them both, with the result that they began to breathe more hurriedly, and to feel as if they had been running uphill, till, as it is called, they were out of breath.

Neither spoke, but suffered in silence, their brains busy with calculations of how long it would be before it was high water, and then how long it would take before the tide sank low enough for the mouth of the cave to be open once more.

Vince probably suffered the more keenly after the light was shut out entirely; but his sufferings were the briefer, for just when his breath was shortest, and he was feeling that he must breathe more rapidly if he wished to keep alive, he heard a loud plashing and wallowing some distance farther in.

That it was a party of seals playing about he was certain, and in imagination he saw them crawling up on to some piece of rock by means of their flappers and plunging down again. Once he heard a pair of them swimming in chase one of the other, blowing and uttering loud, sighing noises as they came near, and then appeared to turn and swim back, to climb up on the rock again, with the effect of dislodging others, which sprang heavily into the water, sending little waves along big enough to make the boat rock perceptibly.

This was just when Vince felt at his worst, and Mike was lying back in the boat breathing hard and in the most hurried way.

It was singular that just then the recollection of a story he had once read in a work belonging to his father came to Vince's mind. True or false, it had been recorded that some French surgeons had been discussing the effect of the imagination upon the human mind, and to test for themselves whether its effects could be so strong as some writers and experimentalists had declared, they obtained permission to apply a test to a condemned convict.

Their test was as follows: It had been announced to the man that he was to die, and that his execution was to be the merciful one of being bled to death. So at the appointed time the culprit was bound and blindfolded in the presence of the surgeons, who then proceeded to lance his arm and allowed a tiny jet of warm water to trickle over the place and down to the wrist.

It is said that, though the man had not lost a drop of blood, he began, as soon as he had felt the lancet p.r.i.c.k and the trickling of the warm water, to grow faint, and after a time sank and sank, till he actually died from imagination.

"And that's what we're doing," thought Vince, as he drew slowly a long, deep breath, and then another and another.

The first was very catchy and strange, the second caused him acute suffering, and the third was deep, strong, and life-inspiring.

"That's it," said Vince to himself--"it is imagination; for if the seals, which are things that have to come up to the surface to breathe, can live in here, why can't I?"

Vince again took a deep breath, and another, and another, and so great a feeling of vigour ran through him that he laughed aloud, and Mike started up.

"What is it?" he said.

"Listen," cried Vince; and he loudly drew breath, and expressed it as loudly, then, "Do that," he cried.

"I--I can hardly get mine. This place is stifling."

"Try," said Vince. "That's right. Again! Better. Now take a long pull. How are you now?"

"Oh, better--better," said Mike eagerly.

"Breathe again."

"Yes, yes; I am breathing better and better. Then the air is coming now?"

"Yes," said Vince drily; "the air is coming fast, and the light can't be very long. There--it's all right, Ladle; we shan't hurt now. But I don't know how we're going to manage when the tide falls, for we shan't dare to go out."

"No," said Mike, whose spirits sank again at these words, "we shan't dare to go out. Do you know, I wish, as you did, that we had stopped on board."

"And not taken all this trouble for nothing. How long should you say it would be before the light comes again?"

"Hours," said Mike; "but I don't mind it so much now that we can breathe better."

"No; it is better," said Vince drily. "I say, I wonder what they are doing at home?"

Vince wished the next moment that he had not said those words, for they had the effect of sinking his companion into a terrible state of depression, while, in spite of his efforts, he was himself nearly as bad.

But then it was before breakfast, and they had hardly touched a mouthful since the morning before.