Rollo in Naples Part 13

Mr. George saw by a glance that the descent into the crater must be safe, for the young men were led by one of the regular mountain guides; and besides, there was a track in the sand, showing that other parties had gone down before. So he said that Rollo and Josie might go.

"You may go down with this party," said Mr. George, "and then you can come up and take care of Rosie while I go down with _our_ guide."

So Rollo and Josie followed the two young men down. Mr. George watched them from above. They went down very easily, for the sand was soft, and the track turned this way and that, so as to avoid the steepest places.

The black lava covered the whole floor of the crater, and Mr. George and Rosie supposed that those who had gone down would be able only to go to the edge of it; but, to their great surprise, they found that the guide, as soon as he reached it, stepped upon it, and walked boldly out, followed by the young men and by Rollo and Josie, like a party of boys walking out upon the ice on a pond.

"Why, uncle George!" exclaimed Rosie, "they are walking over the lava.

Why don't they sink in?"

"I cannot imagine," said Mr. George. "I supposed it was soft."

In fact, it _was_ soft; that is, it was soft enough to flow if it had been on a slope, but yet it was hard enough to walk upon. A current of lava, when it is coming down the mountain side, can often be walked upon while it is still in motion. Its fluidity at the best is very imperfect, and its motion is very slow. The lava which Rollo was upon in the floor of the crater, though pretty nearly cool and hard on the surface, was hot below. Rollo could see the redness of the heat in the holes and crevices. Probably, if a heavy stone were laid upon the bed of lava, it would gradually have sunk into it. And yet persons could walk over it without any difficulty.

Rollo and Josie followed the young men over the lava until they came so near the cone in the centre that if they were to advance farther they would be in danger of having the lava which was thrown up from it fall upon their heads. Here they found some boys, who belonged to the mountain, engaged in getting out small pieces of the lava, where it was hot and soft, and pressing coins into it, to sell to the people above.

Rollo and Josie bought some of these specimens of the boys, and put them hot in their pockets.

While the boys were thus near the cone in the centre of the crater, they were sometimes lost to view from Mr. George and Rosie, on account of the puffs of vapor which the wind blew over them. Rosie was very much afraid whenever this happened. She thought that Josie and Rollo were lost; but Mr. George a.s.sured her that there was no danger.

"I should think there would be a great deal of danger," said she.

"So should I," said Mr. George, "of my own judgment. But I do not go by my own judgment in such cases."

"Whose judgment do you go by?" asked Rosie.

"By the guides'," replied Mr. George. "The guides know all about the mountain. They are up here every day. They have been watching it for years, and they can tell where it is safe to go, and where it is dangerous, better than any stranger. So I give up my judgment entirely, and go altogether by theirs. You will see Rollo and Josie coming back out of the smoke pretty soon, as safe as they went in."

This prediction proved to be true. In a few minutes, on account of some change in the gusts of wind, the ma.s.ses of vapor in the crater broke into openings, and rolled off towards the other side, and in the openings Rosie could see the boys coming back over the black surface of the lava, their footsteps making a curious sound upon it, as if they were walking over clinkers. Very soon they reached the side, and then came toiling up the path which ascended the slope of sand.

Rollo and Josie were both full of enthusiasm in describing what they had seen at the bottom of the crater, and near the cone, and they strongly recommended to Rosie to go down too.

"I'll go with you, Rosie," said Josie, "and show you the way."

But Rosie declined the adventure, and Mr. George told her that she did right to do so.

"Why, what is there to be afraid of?" asked Josie. "There is no danger--not the least in the world."

"True," said Mr. George; "but going into such places does not give so much pleasure to young ladies as it does to such courageous young gentlemen as you. But I wish to go down myself, and I will leave Rosie under your care here while I am gone."

Pretty near where the party stood while engaged in this conversation, several persons were gathered about what seemed to be a fire. A sort of smoke came up from the ground in the centre of the group, and by the side of it were one or two baskets containing eggs, bread, bottles of wine, and other refreshments. Mr. George led the way to this place, and then he found that what seemed to be a fire was really a jet of hot steam and sulphurous gases that was issuing from a cleft among the rocks. The place was very near the crest of the crater, and the people that stood around it were watching to see men cook in the jets of steam.

There was a little level place inside the crevice, just beneath the ground, where they could put eggs and other such things, and after leaving them there a short time, they were found to be nicely cooked. As fast as they were done, the men took them out and sold them to the bystanders.

Mr. George left Rosie and the two boys here while he went down into the crater. The guide went with him to show him the way. In about ten minutes Mr. George returned, and found the three children standing round the _cuisine_, as the men called the place where they cooked. Rollo had been buying some of the eggs, and he and Josie and Rosie were eating them.

"Mr. George," said Josie, "are these boiled eggs, or baked eggs, or roasted eggs, or what?"

"They seem to be steamed eggs," said Mr. George.

"I suppose," said Rollo, "that by digging about here in the sand, we might find a place where it would be just warm enough to _hatch_ eggs."

"No doubt," said Mr. George.

Just then Rollo observed that the two young men whom he and Josie had followed down into the crater were standing at a little distance, and attentively regarding some sort of instrument which they had in their hands.

"I mean to go and see what they are doing," said Rollo.

So saying, he looked into Mr. George's face, and waited to see if Mr.

George had any objection to his going.

"Very well," said Mr. George.

So Rollo went off to the place where the young men were standing, and soon afterwards Mr. George and the others of the party could see that the strangers were showing him the instrument, and apparently explaining it to him. Pretty soon Rollo returned and reported that the two young men were students, and that the instrument which they had was a metallic barometer, and that they were measuring the height of the mountain with it.

This metallic barometer is quite a curious instrument. You will often read, in books, of measuring the height of a mountain, or other lofty place, _by the barometer_; and to most people this is quite a mystery.

The explanation of it is, however, very simple. It is this: The earth is surrounded on all sides by the atmosphere, which, though very light, has a certain weight, and it presses with considerable force upon the ground, and upon every thing that is exposed to it. If, however, you go up from the ground, as, for instance, when you ascend a mountain, the higher you go, the less the pressure is. This is naturally to be expected, for the higher you go in such a case, the less air there is above you to press. Now, a barometer is an instrument to measure the pressure of the air, just as a thermometer measures the heat or coldness of it. A metallic barometer is a new kind, in which the air presses on a curiously contrived ring or band of bra.s.s, and according as it presses more or less, it moves an index like the hand of a watch, which is placed on the face of it. It was such an instrument as this that the two students had, on Vesuvius.

The way in which you use such an instrument to measure the height of a mountain is this: You look at the instrument when you are at the bottom of the mountain, before you begin your ascent, and see how it stands.

There is a little index like the hour hand of a watch, which is movable.

This you set at the point where the other index stands when you are at the foot of the mountain. Then you begin your ascent. You shut up your barometer if you please, and put it in your knapsack, or in the chaise box, or any where else you please. Wherever you put it, the pressure of the air will find it out, and penetrate to it, and as you gradually rise from the surface of the earth, the index, which is connected with the curious bra.s.s ring, moves slowly backward as the pressure diminishes.

This motion continues as long as you continue ascending. If you come to a level place, it remains stationary as long as the level continues. If you descend, it goes forward a little, and then begins to go back again as soon as you once more begin to ascend. Then, when you get to the top of the mountain, you look at it, and you see at once how much the pressure of the air has diminished. From this, by an easy calculation, you tell at once how high you have come.

Mr. George knew all about the barometer, and the means of measuring heights with it, though he had never seen an instrument of this particular kind. He was accordingly very much interested in Rollo's account of it, and he said he had a great mind to go and see it himself.

"I wish you would," said Rollo. "I told them that I thought you would like to see it, and they said that they should be very happy to show it to you."

Mr. George accordingly went to see the instrument, and the students gave him so cordial a reception, that he formed at once quite an intimate acquaintance with them. Indeed they were quite pleased to find a person on the mountain who sympathized with them in their scientific inquiries and pursuits, and was capable of understanding and appreciating them.

They told Mr. George that they were going to remain on the mountain until after dark, in order to see it in its night aspects, and they invited him to remain with them.

"Then to-morrow," said they, "we are going across the mountain down through the back ravines, to study the geological structure of the old lava beds, and so come out at Pompeii."

Mr. George said there could be nothing that he should enjoy more, were it not that he had ladies under his charge, and that he felt bound to accompany them back to Naples.

Rollo, when he heard this invitation, immediately felt a strong desire that Mr. George should go, and that he might go too. He instantly perceived, however, that this was out of the question; but he thought that by cordially falling in with the plan of allowing Mr. George to go, he might, perhaps, be the means of accomplishing it. Many boys, in such a case, when they find that a plan of enjoyment that is proposed is one which they cannot themselves share, do all they can to hinder and oppose it altogether. But Rollo had now travelled about the world so much, and had acquired so much experience, that he was above such folly as this.

"Uncle George," said he, "you can go just as well as not. I can take care of Rosie down the mountain to the Hermitage, and then we shall have nothing to do but to get into the carriage and ride home."

Mr. George saw at once how generous it was in Rollo to make this offer, and he said he would so far accept it as to let Rollo take charge of the party going home from the Hermitage in the carriage; but he felt bound, he said, not to leave Rosie until he had returned her safe to her mother's hands. So he said to the students,--

"I will go down the cone with Rosie and the two boys, and accompany them as far as the Hermitage. There I shall find Mrs. Gray and the carriage.

If Mrs. Gray seems cordially willing to go home with the children alone, I will come back here and join you; but if I find she does not seem entirely willing,--if she looks sober about it,--then I will go back to Naples; though in that case I shall come to Pompeii to-morrow, and shall hope to meet you there."

"I hope the lady will be willing to release you," said one of the students.

[Ill.u.s.tration: COMING DOWN.]

"I have but little doubt that she will," said Mr. George.

Accordingly, after rambling about on the margin of the crater a little time longer, and gathering all the specimens which they required, Mr.

George and the children commenced their descent. One of the students went down with them, in order to accompany Mr. George back. The descent was very easy, for the path led down a slope, where, instead of being rocky as it was where they came up, there was little else but loose sand, so that at every step they took they slid down a great way, and thus went, very fast and very easily, from the top to the bottom.