Part 18

"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 it is to attain to any considerable degree of it, in such cases. So thus, it seems, that Jonas has got a sort of a dial?"

"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, he will know what time it is."

"O, but the difficulty is," said his father, "that the shadow will not come to the same places, at the same hours, on different days. It will come to the meridian line, at twelve, always,--that is, nearly to it; but it will not come to any other lines regularly,--that is, if the object, which casts the shadow, is upright."

"Will any other kind of object carry the shadow regularly?" asked Rollo.

"Yes," said his father, "an object that leans over to the north, so as to point to the North Star. If you and Jonas could put a post into the ground so as to have it point to the North Star, then you could mark, all around it, the places to which the shadow would come for every hour in the day, and afterwards it would come to the same places regularly, or nearly so. It would be near enough for your purposes; and I don't know but that it would be quite a respectable dial for you."

Rollo then asked his father why it was that a post, which pointed to the North Star, would bring a shadow any more regularly to the hour marks, than an upright one would; but he said that Rollo did not know enough, yet, to understand the explanation, even if he were to try to explain it. "Therefore," said he, "you must wait until you study astronomy before you can expect to understand it; but you can now, in the mean time, make such a dial, if you wish to do it."

Rollo did wish to do it very much. He accordingly told Jonas all that his father had said. It seemed very strange to Jonas, that a post, pointing to the North Star, should have its shadows move round any more regularly than a post in any other position. He could not imagine what the North Star could have to do with the shadows. Still, he determined to try the experiment.

A few days after this, Jonas did try the experiment. He got two narrow boards, which were once pickets belonging to a picket fence, one end of each was sharp, so that it could be driven down into the ground. Then he selected a certain part of the yard, in a corner, where the dial would be out of the way, and yet the path to the barn led along pretty near it. The reason why Jonas got two boards was this: he knew that, if he drove only one stake into the ground, and inclined it towards the North Star, it would be very likely to get started out of its proper position; but if he had two, he could drive the second one down perpendicularly from the end of the first, and then nail the two ends together; and that would keep all steady.

After having got every thing ready, the boys waited till the evening before fixing up the dial, because they could not see the North Star in the day time. But when the evening came, they went out, and began their preparations. It was a clear and pretty cold evening, and the stars were out in thousands.

"Which is the North Star?" asked Rollo.

Jonas looked about a minute or two, saying, "Let me see--where's the Dipper? O, I see a part of it; the rest is down behind the barn. It was up high the last time I saw it."

"Where is the Dipper?" said Rollo, looking eagerly in the direction to which Jonas was turned.

"Come this way," said Jonas, "so as to be out of the way of the barn, and you can see it better."

So Jonas pointed out the Dipper to Rollo, with its square body, and long, bent handle. It was at first quite difficult for Rollo to see any thing that looked at all like a dipper; as it consisted only of stars, which it required some imagination to make look like one.

"The handle reaches almost down to the ground," said Rollo.

"Down to the horizon, you mean," said Jonas.

"Is that the horizon?" said Rollo.

"Yes," said Jonas, "where the earth and sky meet. Not long ago the Dipper handle was away up there," he continued, pointing up very high.

"Does the Dipper move?" said Rollo.

"Yes, it goes round and round the North Star, all the time. All the stars that are near the North Star keep going round and round it, once every day."

"And the rest of the stars," said Rollo, "do they go round too?"

"Yes," said Jonas; "only they are so far from the North Star, that they go in larger circles, and so go down below the horizon, and are out of sight sometimes. They come up in the east, like the sun, and go over and down in the west. But they don't go over straight," he added. "They don't come right up straight; and so go directly over. They slant away, off to the south, so as to keep always just so far from the North Star."

"That's curious," said Rollo.

"I think it is," said Jonas. "And they all go together; they don't move about among themselves, at all."

"Don't they?" said Rollo.