"Here, Frank, is the Weather Report. Open it and look at it while I read my letters."
Donald took off the saddle and gave the horse her supper. Then he hurried back to see what Frank had found on the inside of the important-looking wrapper. It proved to be a map with queer, crooked lines all over it, but it did not look at all interesting.
"Here it says temperature," said Frank, pointing to a list of figures in the corner. "Perhaps this is what we want."
"I don't see any numbers there like mine," said Donald, taking his notebook from his pocket.
"Let me help you," said Uncle Robert, laying aside his letters and coming to where they sat on the steps.
They made room for him, and, as he took the map, he explained:
"This, you see, is a map of the United States. These dotted lines tell about the temperature. For instance, look at this one which is marked fifty degrees. At every place in the country that is touched by this line on the map the thermometer stood at fifty degrees at the time the map was made."
[Illustration: United States weather map.]
"See," said Susie, "how crooked the line is. Why isn't it straight, uncle?"
"Because," was the reply, "as I told you, it goes wherever the temperature was fifty degrees. You remember, the first day we had our thermometer, we found that there are many things which affect the temperature. At some places along this line there are prairies, at others forests, at others lakes, and here," pointing to the map, "there are high mountains. All of these things affect the temperature, and that, of course, changes the direction of the line."