A river, creek, lake--in fact, any body of water--is a source of perpetual delight to children. Frank, Donald, and Susie have had the river and creek before them all their lives. Now, under Uncle Robert's teaching, the river will mean very much more to them. They take their first lessons in the work of streams in carving and shaping the earth's surface. The pebbles on the beach and the large, rounded stones will soon have stories of the distant past to tell them. The "Big Book" is opened to them, and they read the stories directly from its pages. CHAPTER XIII.--A RAINY DAY. The children get closer to the question of moisture, its use, and distribution. The rain gauge helps them to measure the rainfall. Then comes the problem of where the water goes after it reaches the ground. "How far down does some of it go?" "When and where does it come out of the ground?" Arithmetic is brought in in measuring the rainfall and its distribution. CHAPTER XIV.--THE WALK AFTER THE RAIN. The problems in Chapter XIII move toward their solution, and new questions are opened. The gully tells of the wearing of the water, and foretells a river valley. The spring helps in the question of underground water. The flowing river quickens the imagination in the direction of the great ocean. CHAPTER XV.--THE BIG BOOK. This chapter should be read by parents to the children, as many sentences need expansion and explanation. Hints are given of great things which lie beyond the child's horizon. Discoveries that have changed mankind are referred to. Children's permanent interests are the keynotes of instruction and the infallible guides of the teacher. To continue and sustain their spontaneous observation and desire for investigation leads directly to the study of the best books, and lays the basis for a thorough and profound study of God's universe. CHAPTER I. UNCLE ROBERT'S COMING. Uncle Robert was coming. His letter, telling when they should expect him, had been received a week before. Every day since had been full of talks and plans for his visit, and now the day was come. Everything was ready. Frank and Donald had harnessed Nell, the old white horse, to the little spring wagon, and had driven to the village to meet the train which was to bring Uncle Robert from New York. Susie, in her prettiest white apron, ran out of the house every few minutes, to be the first to see them when they should come along the road. Mrs. Leonard was putting finishing touches here and there. She went into the kitchen to give Jane a last direction about the supper. Then she went to the east room upstairs, Uncle Robert's room, to be sure that everything was just as she knew he would like it. Susie followed her mother, to see if the violets in the glass on his table were still bright and fresh. She had gathered them herself in the woods that morning. "There they come!" she cried. "I hear the wagon crossing the bridge at the creek!"