Rollo's Experiments

Rollo sat down on one side of the sand-garden, and Nathan on the other, and both busied themselves in digging and building little houses. They both became very much interested, and sat some time very still, until, at length, Rollo looked around to see what Nathan might be doing.

“What are you doing, Thanny?” said he.

“O, I’m making the sand run down through.”

Rollo observed that Nathan had an old tin dipper, which he was holding up in one hand, and putting some dry sand into it with the other. There was a very small hole in the bottom of the dipper, for it was an old one which had been worn out and thrown away; and the sand ran out of this little hole in a fine stream, and it was this which interested Nathan so much.

“O, Nathan,” said Rollo, “let me have the dipper.”

“No,” said Nathan, “I want it myself.”

Rollo would not take it away from Nathan, though he wanted it very much indeed.

“Yes, Nathan,” said he, “let me have the dipper, and I will make you an hour-glass out of it.”

But Nathan said, “No, no,” and moved away a little farther.

Rollo then remembered that such a little boy was generally not interested in any one thing very long, and that, if he should let Nathan alone, he would soon put the dipper down, and then he could have it without any difficulty. So he went on making houses in the sand, and in a few minutes Nathan put the dipper down. Then, soon after, Rollo took it up and put some dry sand into it, and he found that the sand would run very smoothly, in a fine stream, through a small hole there was in the bottom of it.

He determined to make an hour-glass of it. He had seen an hour-glass at his uncle George’s. It was made of glass, big at the bottom and at the top, and narrow in the middle between the two. Through the narrow part in the middle, there was a very small hole, to let the sand run down through; and there was just sand enough put in to run through in an hour. So that, if a person should set the sand to running, he would know when an hour had expired, by observing when the sand had all run through.

Rollo thought that he could make an hour-glass; and he thought it would be a great convenience to him to have an hour-glass in the yard; because it often happened, when he came out to play, that his mother would tell him that he might stay out an hour; and then he had to go in very often to look at the clock, in order to know exactly when the hour had expired.

There were, however, so many little sticks and old leaves in the sand, that it kept getting continually clogged up, and at last Rollo began to get discouraged. He tried to pick out the little sticks; but he found he could not do that, and at last it occurred to him that probably Dorothy had some sand in the house that was cleaner.

He accordingly went in and asked her. She told him that he must wash his own sand, and that would make it clean.

“But haven’t you got some that is clean already?” said he.

“Yes,” said Dorothy; “but you will like your hour-glass better if you make it all yourself.”

So Dorothy told him how to wash sand, for Rollo said that he did not know. She said he must put a little in a basin, and then pump water into it. “When the basin is nearly full of water, you must stir it round, and then pour off the water, and pump in more;—do this until the water comes off clear.”

So Rollo took the basin which Dorothy gave him, and went out to his sand-garden, and put in a little sand. Then he went to the pump, and pumped water into it. Then he stirred it about with his hand. The water immediately became very turbid, and a great many little sticks and leaves came floating up to the surface. Rollo was surprised to find how rapidly the water separated the light things which would float upon the top, from the heavy sand which would sink to the bottom. He kept pouring off the water, and pumping in more, until at length no more sticks and leaves came off, and the water appeared pretty clear. Then he carried the sand away, and spread it out upon a clean board in the sun to dry.

While he was thus at work preparing the sand for his hour-glass, Jonas happened to come by, and asked Rollo what he was doing. Rollo told him that he was making an hour-glass. Jonas looked on for a few minutes, and then he told Rollo that he thought that was a pretty good plan. “And I am going to have a time-keeper, too,” said he.

“Are you?” said Rollo. “What?”

“I am going to make a dial,” said he.

“A dial!” said Rollo; “what, a real dial?”

Rollo had an idea that a dial was exceedingly complicated and difficult to make, or to understand; and, in fact, it is difficult to make one that shall be exact in its indications. He did not think it possible that Jonas could make one.

“Yes,” said Jonas, “a real dial; and I have got a noon mark already.”

“A noon mark!” said Rollo; “what is a noon mark?”

“It is a mark to show when it is exactly twelve o’clock.”

“Let me go and see it,” said Rollo, “while my sand is drying.”

Rollo followed Jonas off into the barn, and when there, Jonas pointed to a small line which he had cut with his penknife upon the barn floor. It began at the foot of one of the posts, by the side of the door, and extended back into the barn exactly straight.

“Is that the noon mark?” said Rollo. He was surprised to see that a noon mark was nothing but a cut with a penknife upon a barn floor.

“Yes,” said Jonas; “that is a meridian.”

“A meridian!” said Rollo, looking upon it with an air of great curiosity and respect.

“Yes,” said Jonas; “a line drawn exactly north and south, is called a meridian line; and that is exactly north and south.”

“What do you call it a noon mark for?” said Rollo.

“Because,” said Jonas, “the shadow of the edge of the door post will always be exactly upon it at noon. So that I can always tell now when it is noon, by the shadow of the post upon my noon mark, if the sun shines.”

All this was very new and very curious to Rollo. He had never seen or heard of a noon mark before; and it seemed to him a very simple and beautiful way of knowing when it was noon. He asked Jonas how he found out about it, and Jonas told him that he had been reading about it in a book on astronomy.

“Your father let me have the book,” said he; “and see my chalk marks for the sun’s shadow.”

Rollo looked, and found that Jonas had put down quite a number of chalk marks along in a line, where they had first began to mark the place where the shadow of the door reached into. Rollo and Lucy had forgotten all about their plan of making such a series of observations; but Jonas had gone on regularly, making a mark every Monday, at noon, precisely. As the sun, at that season of the year, was going round farther and farther to the south every week, it shone in farther and farther upon the floor, so that each chalk mark was farther in than the one made the week before.

In order to make his marks at the right time, Jonas wanted to know, every Monday, when it was precisely twelve o’clock, and this led him to make his noon mark, having seen the account of it in the book which Rollo’s father had lent him. He learned there that the shadows of all upright objects are cast exactly north at twelve o’clock, or rather very nearly north; near enough for his purposes. Now, as the post of the barn door was upright, he knew that the shadow of it would be in the north and south line at noon. Of course, if he had a north and south line, or a meridian line, as it was called in the book, drawn upon the floor, he knew that he could tell when it was noon, by the shadow of the post coming then exactly upon that line. He explained this all to Rollo, and Rollo was very much pleased with it indeed. He determined to have a noon line somewhere in the house.

Rollo asked Jonas what was the way to draw a noon line. Jonas told him that there were several ways. One way, he said, was to observe some day, by the clock, when it was exactly noon, and then to mark, upon the barn floor, the line where the shadow of the edge of the post fell precisely at that moment. Another way was to get a compass needle, and put it down upon the floor, and then draw a north and south line precisely in the direction that the needle indicated. That would, of course, be a north and south line, because the compass needle always pointed north and south. He said that he adopted both these methods to make his noon line. First, he got a compass needle, which Rollo’s father had lent him, and put that down upon the barn floor just at the foot of the door post, and observed the direction; and he also noticed when it was twelve, by the clock in the house, and he found that, when it was twelve by the clock, the shadow of the post came exactly to the line indicated by the direction of the compass needle; and so he knew that that was a correct meridian line.

JONAS’S DIAL

That evening, Rollo told his father about his hour-glass, and also about Jonas’s noon line. His father said it was very difficult to draw a meridian line.

“O no, father,” said Rollo; “Jonas has drawn one, and he told me how, and it was a very easy way.”

“Yes,” said his father, “it is easy to draw something which you can call a noon mark; but it is a very difficult and delicate operation to do it with any considerable degree of exactness.”

“I think that Jonas’s is exact,” said Rollo.

“It probably may be as exact as he could make it with his means and instruments; but there are a great many sources of error which he could not possibly have avoided.”

“What?” asked Rollo.

“Why, in the first place, the clock is not exact. It is near enough to answer all the purposes of a family; but it may often be a minute or more out of the way. Then besides, while Jonas is going from the clock out to the barn, the shadow is slowly moving on, all the time; so that he cannot tell exactly where the shadow was, when it was precisely twelve by the clock.

“Then again, it is not always exactly noon when the shadow comes to the north and south line. It varies a little at different seasons of the year, though it is so near that we say, in general terms, that at noon all shadows of upright objects point to the north. Still, it is not precisely true, except on a very few days in the year. Then, again, the post of the barn door is not exactly upright.”

“I thought they always made door posts exactly upright,” said Rollo.

“They do make them as nearly upright as they can, with the common carpenters’ instruments; but they are not exact. To set a post of any kind, with great precision, perpendicular to the horizon, would require very expensive mathematical instruments, and very laborious and nice observations. Then, again, if the clock had been exact, and the post perfectly upright, Jonas could not have marked the place of the shadow exactly. The shadow has not an exact and well-defined edge; and then, even while he was marking at one end, the shadow would be moving along at the other end, and so his noon mark would not be exactly straight.”