"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."

It had come. There was already quite a line of figures in each of their notebooks. Now they could see what this other record was like. As he left the post office he stopped to look at the old thermometer beside the door. Then he mounted Nell and rode down the village street and out into the pleasant country road.

Uncle Robert was waiting for him on the porch, and as Donald rode away to the barn, after giving him the mail, he heard him say:

"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."

[Ill.u.s.tration: 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."

"You say Chicago is the nearest station to us, uncle," said Frank, looking down the temperature column. "My record for that day is not so very different from the one given here for Chicago."

"Which shows that yours is probably as nearly correct as this is," said Uncle Robert, with an encouraging smile.

"But I haven't one number in my book like that," said Susie, looking disappointed. "I don't see why."

[Ill.u.s.tration: Susie's notebook]

"I do," replied Uncle Robert. "You make your record at noon, and of course, it is warmer then. That is what your book says, does it not?"

"Yes," said Susie, "every number in my book is more than that one."

"That is right," was the reply, "for this record was made at eight o'clock in the morning, which is nearer Frank's hour than it is yours.

So we would expect his to be nearer like this than yours, wouldn't we?"

"It isn't like mine either," said Donald.

"We may have one some time that will be more like yours," said Uncle Robert, "for these records are made at eight in the evening as well as in the morning."

"Uncle," said Frank, looking closely at the map, "here it says 'High,'

and there it says 'Low.' What does that mean?"

"It means," said Uncle Robert, "that here there is a low barometer, and there the barometer is high."

"Barometer," said Donald. "What is a barometer, uncle? Is it like a thermometer?"

"Well, not exactly," was the reply. "With the thermometer, you know, we tell the temperature of the air, and with the barometer we tell how heavy it is."

"How heavy the air is!" exclaimed Susie. "How funny! Why, uncle, air doesn't weigh anything, does it?"

"More than you think, little girl," said Uncle Robert, smiling. "But perhaps we can prove whether it does or not. Frank, will you get a pail of water? Donald, see if you can find a cork some place; and Susie, run in and get a tumbler."

When all was ready Uncle Robert asked Frank to fill the pan with water, and Donald to put the cork into it.

[Ill.u.s.tration: Experiment No. 1.]

"There," said Donald, as the cork floated about on the pan of water.

"But I want the cork on the bottom of the pan," said Uncle Robert, "not on the top of the water."

"It won't stay there," declared Donald, pushing it into the water again and again with his finger. "It is too light. Corks always float."

"How can we make it go to the bottom?"

No one could tell. The children looked puzzled.

"Let us see what this will do," and, taking the gla.s.s from Susie's hand, Uncle Robert turned it over the cork, pressed it down into the water as far as it would go, and held it there. Looking through the gla.s.s, they could see the cork lying on the bottom of the pan.

"Why, Uncle Robert!" exclaimed Susie, "what--how--"

"It's the gla.s.s that does it," declared Donald.

"But the gla.s.s doesn't touch the cork," objected his uncle.

"There's air in the gla.s.s," said Frank, who had been looking at it quietly as the others talked. "That is what presses it down."

"If it's air," said Donald, "why didn't it go down before the gla.s.s was put over it? There was just as much air about it then, and more, too."

"Let go of the gla.s.s, uncle," said Frank, "and see what it will do."

Uncle Robert did so, and the gla.s.s instantly turned over, while a big bubble of air escaped through the water.