It was a busy time on the farm. Only when the day's work was over and they were gathered in the sitting-room was there time for the long talks with Uncle Robert that they all enjoyed so much.

"It's wonderful," said Mr. Leonard one evening, looking up from his paper, "how fast the corn is growing. Even the late planting is coming on."

"That's because the weather is so warm," said Donald.

"I wonder what makes it warm?" said Uncle Robert.

"Why, Uncle Robert," exclaimed Susie, "it's spring! That's what makes it warm."

"But what makes it spring, little girl?" asked Uncle Robert.

"Why, it is always spring in May," said Susie.

"I know of a country where it is spring in September," replied Uncle
Robert.

"How can it be?" asked Susie. "I thought springtime always came in May."

"What makes us know that it is spring?" asked Uncle Robert.

"Oh, it gets warmer all the time. The birds come, things begin to grow, and the flowers bloom."

"But what makes all this happen just now?"

"It's the sun," answered Donald from the floor, where he was playing with his great St. Bernard dog, Barri. "You know it rises earlier and sets later every day now than it did a while ago. It's hotter too."

"It goes higher at noon," said Frank. "In the middle of summer it is almost straight over our heads, and in the winter it seems ever so much farther to the south. I've often noticed that."

"So have I," said Donald. "And in the winter the shadows are longer than they are in summer. It must be because the sun isn't so high up."

"Aren't shadows funny?" said Susie. "One day when I was coming in to dinner, just for fun I tried to walk on my shadow, and I could step on my head."

"I've done that lots of times," said Donald. "But it's a strange thing. Sometimes I can step clear over my head—I mean in the shadow—and then again I have to step on it."

"And when you jump," said Susie, "it spoils it. The shadow always jumps too."

"What kind of weather was it when you had to jump to it?" asked Uncle
Robert.

"I don't remember," said Donald. "Would the weather make any difference?"

"I remember," said Susie, "because one time when I was jumping that way
I fell down and was almost buried in the snow.

"Then it was winter, wasn't it?" asked Uncle Robert.

"It must have been," said Frank.

[Illustration: Shadow stick.]

"And since you told us that the shadows at noon tell why it is warmer in summer than in winter I've been watching them. They get shorter all the time." "How would you like to measure the shadows every day," said Uncle Robert, "and see if you can find out when they are shortest and when they are longest?"

"How can we?" asked Susie. "Shadows are so queer."

"Yes," said Uncle Robert, "shadows are queer, but, if we take one that doesn't jump as yours does, don't you think we can measure it?"

"Of course we can," said Frank. "We can use the house. That always stands still."

"The house might do," said Uncle Robert; "but wouldn't it be better to have a shadow stick?"

"Where can we get one?" asked Donald.

"What is it made of?" asked Frank.

"It is like this," said Uncle Robert, taking paper and pencil from his pocket. "There is one long piece of board, and one short one nailed to the end—so," drawing it on the paper.

"Oh, that's easy enough made," said Donald. "We can do it ourselves right here in the tool house."

"Let's make it to-morrow, Don," said Frank.

"It must be set up some place with the upright end turned toward the south, so that just at noon the shadow of the short piece may fall straight on the board. By drawing a line across the board at the top of the shadow and marking the date on it, we can tell how the length of the shadow changes."

"Uncle," asked Donald, "when it is winter here, is it summer in some other part of the world?"

"Yes," was the reply, "and now that our summer is coming, the people there are beginning to have winter."

"Then," said Frank, "when it gets cooler here in the fall it is growing warmer there, and that would make their spring come in September, wouldn't it? Do you see, Susie?"

[Illustration: Eskimo scene.]

"Yes," answered Susie, "but it seems all mixed up. I thought it was the same as it is here all over the world."

"Oh, I didn't," said Donald. "I've read about countries where it is summer all the time, and is so hot that the people don't do anything but lie under the trees and sleep. And there are other countries where it is winter all the time, and the people dress in furs and make their houses of snow and ice. I read all about it in a book once, but it didn't tell why it was so. I knew, of course, the sun had something to do with it."

"Why, you know, Don," said Frank, "we learned all that in our geography at school."

"Yes," said Donald, "but I never thought about that in the geography as meaning any real country."

"What did you think it meant?" asked Uncle Robert.

"Oh," said Donald, "just a lesson in the book."

"Well," said Frank, "I always thought it was some country, but I never knew where. I didn't think much about it after I said the lesson."

"I should think not," said Uncle Robert, not sorry that the teacher had gone away and the school had been closed.

"I wish when books tell things they'd tell why they're so," said Frank.

"Perhaps if we think about these things," said Uncle Robert, "we may be able to answer some of the 'whys' for ourselves."

"We can tell by the thermometer just how warm it is every day," said
Susie, "but it won't tell us why."

"The shadow stick may help us there," said Uncle Robert.

"I am afraid I shall forget," said Donald.

"I have some little notebooks in my trunk," said Uncle Robert. "Suppose I give you each one and let you write down what the thermometer and the shadow stick say every day."

"What fun that'll be!" cried Susie. "When may we begin?"

"To-morrow morning, if you like," replied her uncle. "I will get the books for you now."

He went away to his room, and soon returned with the notebooks.

"I'll tell you, uncle," said Frank as he thanked Uncle Robert for his book, "how would it do for each of us to look at the thermometer at a different time of the day?"

"The very thing!" replied Uncle Robert, well pleased. "You are always up early, Frank, so suppose you look at six in the morning, Susie at twelve o'clock, and Donald at six in the evening. How will that do? Then we shall have the record for the whole day."

"I think it will be such fun!" said Susie. "I wonder if our books will be very different."

"What makes you think they will be different?" asked Uncle Robert.

"It's always hotter at noon than it is at night or in the morning," said
Susie.

"Do you know," said Uncle Robert, "there are places all over the United States where such records are kept? They are published, and I am to have them sent to me every week."

"I wonder if ours will be like them," said Donald, turning over the pages of his notebook.

"Even if they should be different." said Uncle Robert, "they may be just as true."

"We'll get up early and start the shadow stick the first thing in the morning," said Frank, "so as to have it ready by noon."

"How do you know when it is noon?" asked Uncle Robert.

"We look at the clock," said Susie.

"But noon by the clock is not always noon by the sun," replied Uncle
Robert.

"How can that be?" asked Donald.

"It is noon somewhere on the globe every minute of the twenty-four hours," said Uncle Robert. "The sun is always setting and always rising somewhere."

The children were puzzled.

"I don't see how that is," said Donald.

"Let us see if we can find out," said Uncle Robert. "Frank, you stand at the east end of the room, Donald at the west, and Susie in the middle. Now, we'll play that Frank is in New York, Susie here at home in Illinois, and Donald in Denver. I'll take the lamp and be the sun. You are shadow sticks, you know. Now watch the shadows, and see when they point directly north."

Uncle Robert took the lamp and walked slowly from the east side of the room.

"My shadow points north," said Frank as Uncle Robert passed him.

"Now mine does," said Susie.

"And mine last of all," said Donald.

Uncle Robert took out his watch. It was ten minutes past eight.

"That is Susie's time," he said. "Would it be the same in New York,
Frank?"

"I think it would be past that," said Frank, "but I don't know how much."

"It is ten minutes past nine by the watch in New York," said Uncle
Robert.

"When would it be that time in Denver?" asked Donald.

"In an hour by the watch," said Uncle Robert, "but it would not be the same by the sun."

"Then the watches don't tell the true time, do they?" said Frank.

"The sun's shadows give us the true time," said Uncle Robert. "We will study the shadows, and by and by may learn how the watches and clocks are regulated. But how do you think people told the time before they had clocks?"

"It must have been by the sun," replied Frank.

"I can tell by the sun when it is noon," said Donald, "but I don't see how any one can tell any other hour that way."

"How do you know when it is noon?"

"Why, the sun is highest at noon." said Donald. "and the shadows point straight toward the north."

"Early in the morning they point to the west," said Frank, "and in the evening they point to the east."

"The people who lived in the world many hundred years ago observed the same thing," said Uncle Robert. "There was nothing so strange to them as the rising and setting of the sun. They loved the light that came with it. They feared the darkness that followed its going away. They told many interesting stories to explain this continued appearance and disappearance. Some thought the sun was a king riding through the sky in a golden chariot. Others looked upon it as a god and worshiped it.

"They soon learned that when it went away it was sure to come again, and as they saw how regularly it moved, they felt there must be some power back of it to guide it. Through this they were led to a belief in a Being that controlled all things.

"They watched the shadows, too, and saw them change just as you see them every day. They learned that the shadow is shortest when the day is half gone, and they called that time midday. So, by studying the length and direction of the shadows, they soon became able to judge the time of day.

"Then some one thought to set up a rod and mark the places where the shadow fell at sunrise, at sunset, and at midday. The space in between was divided for the hours. This was called a sun dial and was the first instrument ever made for telling time."

"When was the first one made?" asked Frank.

"That is not known," replied Uncle Robert, "but we read in the Bible of the sun dial of King Ahaz, who lived about eight hundred years before the time of Christ. That is the first record we have of one."

"How was it made?" asked Donald.

"I do not know how the one King Ahaz used was made," said Uncle Robert, "but I can show you how one looked that I saw in an old garden in England. This," drawing a half circle, "is the dial on which the hours were marked. Around this dial there was a border, much cracked, and crumbling away, but I could read the words, 'The sun guides me, the shadow you.' The rod, or gnomon, as it is sometimes called, stood just halfway between the ends. Where would the noon shadow fall, Susie?"

[Illustration]

"In the middle, wouldn't it?" answered Susie.

"And the morning shadow would fall on the west and the evening shadow on the east side," said Frank.

"Now we'll put in the shadow stick," said Uncle Robert, drawing a triangle on the paper.

"Why don't you make it stand up straight?" asked Donald.

"The shadow does not tell the truth," said Uncle Robert, "unless it points in the same way that the north pole does, and that, we know, points to the north star. I will explain this some other time."

"Couldn't we make a sun dial?" asked Donald. "I don't believe it would be very hard."

"You could make one easily," answered Uncle Robert.

"But let's have the shadow stick first," said Frank.

Susie went to the window and looked out at the clear star-lighted sky.

"Uncle," she said, "the stars all look alike to me, only some are little and some are big. How can people know them by their names?"

"Just as anything else is known, dear," replied Uncle Robert, "by close and careful study."

"I wish we could study the stars," said Frank.

"We will some time," replied Uncle Robert. "Come out on the piazza now, and I will show you the north star. That will be a good beginning."