The sky never falls down because there is nothing to fall. What we see and call the sky is the reflection of the sun's rays on the belt of air that surrounds the earth. That beautiful blue dome that we sometimes hear spoken of as the roof of the earth is just the reflected light of the sun on the air.

The atmosphere of the earth consists of a mass of gas extending to a height which has been variously estimated at from forty-five to several hundred miles, possibly five hundred, and bearing on every part of the earth's surface with a pressure of about fifteen pounds per square inch.