Take the stopper out of a bottle and endeavor to pour water into it rapidly and see what happens. (See Fig. 1.) One of the laws in Physics is that no two bodies can occupy the same space at the same time. After doing this experiment, you will come to the conclusion that the bottle does contain something, and that “something” is matter, and that matter is air. There is in the bottle probably as important a thing as you could possibly conceive of, because even this earth without its ocean of air would be a world of desolation; for air sustains life itself, and when agitated, develops great strength. It may be whirled about into a hurricane blast and assume such violent proportions that villages will be swept away, and great waves of water will be raised, upon which ships can be tossed about like so much chaff. We all know that air can become so cold that great suffering will be caused, and so hot that it will make life almost unbearable. We really live in an ocean of air. [Illustration: Fig. 1 ] [Illustration: Fig. 2 ] THE OCEAN OF AIR As the fishes live at the bottom of the ocean of water, mankind lives at the bottom of an “ocean of air.” (See Fig. 2.) No one is absolutely certain about the depth of this air, but it has been estimated as low as forty miles and as high as two hundred miles. Balloons have gone up to a height of nearly nineteen miles (100,320 feet). We do know that the higher we go, the thinner the air becomes. It is practically impossible for man to ascend into the air more than five or six miles, owing to the fact that the air above that height is so thin that there is not enough to breathe. Naturally, the air at the bottom is more compact because of the vast amount of air above. The air is a great weight lying upon us—14.7 pounds per square inch of surface. HOW TO PROVE BY EXPERIMENT THAT AIR HAS WEIGHT The air-globe is a piece of apparatus for demonstrating that air has weight. (See Fig. 3.) First, the air-globe is weighed and then the air is pumped into it; its stop-cock is closed and the globe is reweighed. It will be found to have gained in weight. This is conclusive that air is matter and that it has weight. [Illustration: Fig. 3 ] [Illustration: Fig. 4 ] Of great importance to us in the study is the next fact, that air exerts pressure on everything about us and upon ourselves. EXPERIMENT NO. 2 A tumbler is filled with water and a piece of paper placed over the top of it. The glass is then inverted, holding the hand over the paper so that none of the water will come out. On taking the hand away, although the glass of water is inverted, the contents do not leave the glass. (See Fig. 4.) [Illustration: Fig. 5 ] CONCLUSION