If a man could start out when the sun rose in the morning and keep up with it all day long, go over the side of the world when the sun set and keep up with it on the other side of the world, he would be back again where he started the next morning. He then would have gone round the world in one day. But to do that he would have to travel over 1,000 miles an hour to keep up with the sun for each of the twenty-four hours in a day and night.

All around the outside of the world—as you probably know—is an ocean of air that covers everything on the world as the ocean of water covers everything in the sea. What you probably don't know is that this ocean of air is wrapped only round the World—it does not fill the sky.Men and animals live in this ocean of air as fish live in the ocean of water, and if a huge giant picked you out of the air you would die just as quickly as a fish does when taken out of the sea. The air is thick near the ground but gets thin and thinner the higher up you go off the ground. That's why airplanes can go up but a few miles high—there is not enough air to hold up the plane, for the plane must have air to rest on and for its propeller to push against just as a boat in the water must have water to rest on and water for its propeller to push against. Or if if s a jet plane, it must have air to feed its jet motors. An airplane could not rise beyond the ocean of air and sail off into the sky where there is no air any more thana steamship on the sea could rise out of the water and sail off up into the air.

There is only one thing that men can send up high enough to travel above the ocean of air. That is a rocket which doesn't depend on air for its motor or to hold it up.