"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.
[Illustration: 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."