"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." CHAPTER VII. THE BAROMETER. One day when it was Donald's turn to go for the mail he found among Uncle Robert's letters a small paper. On the wrapper he read "United States Weather Report."