"No, it becomes hard when it is very, very cold." "How cold, uncle?" asked Donald, looking at the thermometer. "Thirty-nine or forty degrees below zero," was the reply. "In the coldest of countries alcohol thermometers are used. It must be much colder than that to freeze alcohol." "Why is mercury used, uncle?" asked Frank. "Because it takes a very great heat to make it boil." said Uncle Robert. "Then you have seen how quickly it shows a change of temperature. When it is warm we call it a high temperature, and when it is cold it is called a low temperature." "That is because the mercury goes up when it is hot, and down when it is cold, isn't it?" said Donald. "I wonder how it would feel if it was forty degrees below zero. See, it is away down to there!" "Do you remember that day last winter when Peter froze his ears driving to town?" asked Frank. "Well, it was twenty below that day at the post office. I saw it. But father is calling me; I must go." CHAPTER IV. WITH THE ANIMALS. "Don't forget to set that hen, Donald," called Mr. Leonard, as he and Frank went away together. "I think there are enough of those Plymouth Rock eggs for one more setting." "You ought to see our little chickens, Uncle Robert," said Susie. "They are just too cunning for anything." "When you go to set the hen, Donald," said Uncle Robert, "I will go with you. Then you can show me everything about the barn." Donald went to the storeroom and soon came back with the eggs. "There are thirteen," he said, as he joined Uncle Robert in the porch, "but I think she can take care of them. She's one of the largest hens we have." Then together they went to the henhouse, which stood next to the barn. The chickens, seeing the basket in Donald's hand, ran toward him. "You needn't think I am going to feed you again so soon," he said. "You have had one breakfast this morning." Donald always talked to all the animals as though they could understand him. [Illustration: The poultry yard.] The mother hens paid no attention. With quiet dignity they walked about, their broods of fluffy little chicks looking like balls of gold in the sunshine. With a "Cluck! cluck!" each anxious mother called her children to her as her sharp eyes discovered some new dainty. Then the greedy little yellow things ran as fast as their short legs could carry them to be the first to take the good things from the self-sacrificing mother. "How many little chickens are there?" asked Uncle Robert as they stopped to watch them. "There are forty-six hatched," said Donald. "Three hens are setting, and this one will make four." "I see you have some fine turkeys, too," said Uncle Robert. The big turkey cock spread his tail and strutted about before them as if he understood how much he was admired. "Mother thinks a great deal of her turkeys," said Donald. "They are much harder to raise than the chickens. But mother knows just how to do it. We don't lose many."