"This proves that air is an actual substance, although we cannot see it. It occupies all the space of the bottle, and so long as it is in the bottle, the other substance, water, cannot enter.""But," said Willie, "there is just one other thing to remember about the bottle. The water did enter a little way into the neck of it when you pressed it down. That proves that you were able to press the air into a smaller space. Teacher says air is compressible.
"Then, too, when you left off pressing the bottledown, the air in it sprang back to its former bulk,and the water that had entered the neck was forced out again. This proves that air is elastic."SUMMARY
Air is an actual substance, although we cannot see it. There is air everywhere. Air occupies space, and is compressible.
Lesson 27
More about the Frog
"Have you got over your dislike for the poor little frog, Norah?" asked Fred. "We have been learning some wonderful things about him today. Would you like to know how he breathes? It is all very strange." "Yes," said Norah, "I should like to hear all aboutit."