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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 enou...
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 ...
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 ...
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. Roll...
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, to...
"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...
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 ...
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 ...
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 shado...
"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 day...
"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...
"Why, father, he could make the mark right along quick."
"No matter how quick he might make it. It would take some time, wouldn't it?"
"Only a very little," said Rollo.
"And do you suppose the sun would stand still, even during that little time, so as to let the shadow remain stationary?
"However," continued his father, "I don't say this to disparage Jonas's noon mark. I dare say, it is accurate enough for his purposes. He only wants to know from it when it is time for him to come in to dinner, or something like that. I only want you to understand what exactness is, and to see, a little, how difficult ...
"Why, it only tells him what o'clock it is at one hour in the day," said Rollo. "But I think he might make it do for all the afternoon and forenoon."
"How?" inquired his father.
"Why, all he has got to do is to watch some day when it is nine o'clock, and ten o'clock, and so on, every hour; and then make a line where the shadow comes every hour, just as he did for twelve o'clock. Then he will have marks for every hour in the day, and when the shadow comes along to these marks, one after another...