"Perhaps we can find one nearer than the post office," said Uncle Robert. "Susie, would you know one if you saw it?" Susie shook her head. "I would," said Donald. "Well," said Uncle Robert, "please go to my room, and if you find a thermometer bring it to me." Donald soon returned, and when Susie saw what he had in his hand she exclaimed: "Is that a thermometer? I never saw anything like that at the post office." "Well, I should think not," said Donald. "This isn't much like the old thing they have up there." "What does it say?" asked Uncle Robert. "Sixty-eight degrees above zero," said Frank, taking the thermometer in his hand. [Illustration: Thermometer.] "That isn't cold, is it, uncle?" asked Donald. "That's just right for the house," said Uncle Robert. "How is it out of doors?" "Let's take it out and see," said Frank. Out on the porch they went and eagerly watched the thermometer. "It's moving--it's going down!" cried Donald. "I'll hang it on this nail," said Frank. "When they looked again Donald said: "It's fifty-six now." "How much colder is it than it was in the house?" asked Uncle Robert. "Twelve degrees," said Frank, counting up the column. "Oh, let's take it in by the stove," said Susie, "and see how far it will go up." "What makes you think it will go up by the stove?" asked Uncle Robert. "Well," answered Susie, "if it goes down when it is cold I should think it would go up when it is warm." Susie took the little instrument, and, going into the kitchen, held it close to the stove. "Come," she called, "it is going up already. See!" "How fast it moves!" said Donald. "Hold it close to the stove, Susie. Maybe it will go to the very top." "Let us put it in cold water," said Frank. "It won't hurt the thermometer, will it?" "Not at all," was the reply. "Try it." So they held it in the bucket of cold spring water. "How fast it goes down now!" said Susie. "I wonder if it will go lower than it did out on the porch. It's down to forty-eight." "Why does Jane set the kettle of cold water on the stove?" asked Uncle Robert, pointing to it. "To boil the water," answered Susie. "What makes the water boil?" "Why, the fire, of course." "How long will the stove stay hot?" "As long as there is fire in it." "Longer than that," said Donald. "It doesn't grow cold the minute the fire is out." "What becomes of all the heat?" asked Uncle Robert. "Oh, it goes all round the room." "Let's put the thermometer in the hot water," said Susie. "Oh, see it go up!" said Donald. "It is one hundred and fifteen already." "What is the difference in degrees between the cold and the hot water?" asked Uncle Robert. "Sixty-seven degrees," said Frank. "What makes the difference in degrees?" "The difference in the heat," said Frank. "If the water was boiling and the thermometer large enough," said Uncle Robert, "it would go to two hundred and twelve." "That would be ninety-seven degrees higher," said Frank.