"Do you know what water weighs?"

"No, but I know that it is heavy."

"Well, a square yard of air weighs two pounds and a half, but a square yard of water weighs two thousand pounds. Now, can you calculate the weight of the water that is on your back and pressing on your sides when you swim?"

"No, I cannot."

"You are not sufficiently up in arithmetic to do that, Willis?"

"No."

"Nor am I either, Willis; but let me ask you how it is that the waves do not carry you along with them?"

"Because one wave neutralises the effect of another."

"Very good; but how is it that these ponderous waves, coming down upon you, do not crush you to atoms by their mere weight?"

"Well, I suppose that liquids do not operate in the same way as solids: perhaps there is something in our bodies that counterbalances the effect of the water."

"Very likely; and if such be the case as regards water, may it not be so also as regards air?"

"But I do not feel air; whereas, if I go into water, I not only feel it, but taste it sometimes, and I cannot force my way through it without considerable exertion."

"That is because you are organized to live in air and not in water.

You ask the smallest sprat or sticklebake if it does not, in the same way feel the air obstruct its progress."

"But would the stickleback answer me, Master Fritz?"

"Why not, if it is polite and well bred?"

"By the way, Willis," inquired Jack, "do you ever recollect having lived without breathing?"

"Can't say I do."

"Very well, then; had you felt the weight of the air at any given moment, it must have produced an impression you never felt before, but you have not, because circumstances have never varied. A sensation supposes a contrast, whilst, ever since you existed, you have always been subject to atmospheric pressure."

"Ah, now I begin to get at the gist of your argument. You mean, for example, that I would never have appreciated the delicate flavor of Maryland or Havanna, had I not been accustomed to smoke the cabbage-leaf manufactured in Whitechapel."

"Precisely so; and take for another example the farm of Antisana, which is situated about midway up the Cordilleras, mountains of South America. When travellers, arriving there from the summits which are covered with perpetual snow, meet others arriving from the plain where the heat is intense, those that descend are invariably bathed in perspiration, whilst those that have come up are shivering with cold and covered with furs. The reason of this is, that we cannot feel warm till we have been cold, and _vice versa_."

"Our bodies," resumed Fritz, "however much the thermometer descends, never mark less than thirty-five degrees above zero. In winter the skin shrinks, and becomes a bad conductor of heat from without; but, at the same time, does not allow so much gas and vapor to escape from within. In summer, on the contrary, the skin dilates and allows perspiration to form, a process that consumes a considerable amount of latent heat. Starting from this principle, it has been calculated that a man, breathing twenty times in a minute, generates as much heat in twenty-four hours as would boil a bucket of water taken at zero."

"If means could be found," remarked Jack, "to furnish him with a boiler, by fixing a piston here and a pipe there man might be converted into one of the machines we were talking about the other day."

"Were I disposed to philosophize," added Fritz, "I might prove to you that for a long time men have been little else than mere machines."

Before night they had run about thirty miles further to the north-east, without seeing any thing beyond a formidable bluff, guarded by a fringe of breakers, that would soon have swallowed up the _Mary_ had she ventured to reach the land. It was necessary however to obtain fresh water at any price before they resumed their voyage.

It was to be feared that all the islanders of the Pacific were not in expectation of a great Rono, consequently Willis suggested that it would be as well to search for an uninhabited spot. The only question was, how long they might have to search before they succeeded; for they knew that there were plenty of small islands in these latitudes unencumbered by savages, and furnished with pools and springs of water.

Night at length closed in upon them, and with it came a dense mist, that enveloped the _Mary_ as if in a triple veil of muslin.

"Willis," inquired Jack, "what difference is there between a mist and a cloud?"

"None that I know of," replied the Pilot, "except that a cloud which we are in is mist, and mist that we are not in is a cloud. And now, my lads," he added, "you may turn in, for I intend to take the first watch."

Before turning in, however, all three joined in a short prayer. The young men had not yet forgotten the pious precepts of their father.

Prayer is beautiful everywhere, but nowhere is it so beautiful as on the open sea, with infinity above and an abyss beneath. Then, when all is silent save the roar of the waves and the howling of the winds, it is sublime to hear the humble voice of the sailor murmuring, "Star of the night, pray for us!"

That night the star of the night did pray for the three voyagers, for the rays of the moon burst through the darkness and the mist, and fell upon a long line of reefs under the lee of the pinnace. Had they held on their course a few minutes longer, our story would have been ended.

CHAPTER XXI.

LYING TO--HEART AND INSTINCT--SPARROWS VIEWED AS CONSUMERS--MIGRATIONS--POSTING A LETTER IN THE PACIFIC--CANNIBALS--ADVENTURES OF A LOCKET.

The glimpse of moonshine only lasted a second, but it was sufficient to light up the valley of the shadow of death. All around was again enveloped in obscurity. The moon, like a modest benefactor who hides himself from those to whose wants he has ministered, concealed itself behind its screen of blackness.

The pinnace was thrown into stays, and they resolved to lie-to till daybreak. There might be rocks to windward as well as to leeward; at all events, they felt that their safest course lay in maintaining, as far as possible, their actual position; and, after having returned thanks for their almost miraculous escape, they made the usual arrangements for passing the night.

Next morning they found themselves in the midst of a labyrinth of rocks, from which, with the help of Providence, they succeeded in extricating themselves. The rocks, or rather reefs, amongst which they were entangled, are very common in these seas. As they are scarcely visible at high water, they are extremely dangerous, and often baffle the skill of the most expert navigator.

Whilst Willis steered the pinnace amongst the islands and rocks of the Hawaian Archipelago, Fritz kept a look-out for savages, fresh water, and eligible landing-places. And Jack, after having posted up his log, set about inditing a letter for home.

"The voyage," said he, "has lately been so prolific in adventure, that I scarcely know where to begin."

"Begin by saluting them all round," suggested Fritz.

"But, brother of mine, that is usually done at the end of the letter," objected Jack.

"What then? you can repeat the salutations at the end, and you might also, for that matter, put them in the middle as well."

"I have written lots of letters on board ship for my comrades,"

remarked Willis, "and I invariably commenced by saying--_I take a pen in my hand to let you know I am well, hoping you are the same_."

"What else could you take in your hand for such a purpose, O Rono?"

inquired Jack.

"Sometimes, after this preamble, I added, '_but I am afraid_.'"

"I thought you old salts were never afraid of anything, short of the Flying Dutchman."

"Yes; but the letters I put that in were for young lubbers, who, instead of sending home half their pay, were writing for extra supplies, and were naturally in great fear that their requests would be refused."

"I scarcely think I shall adopt that style, Willis, even though it were recognized by the navy regulations."